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This is a summary of the papers published in the Special Section titled "Fast Physics in Climate Models: Parameterization, Evaluation, and Observation" (https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)2169‐8996.FASTPHYS1), as requested by the JGR‐Atmosphere Chief Editor, Professor Minghua Zhang. Key Points: Motivation for this special section is presentedPapers in this special issue are summarizedFuture challenges facing fast physics in climate models are discussed [ABSTRACT FROM AUTHOR]

Intracloud (IC) lightning flashes are normally initiated below 10 km and start with upward negative leaders. In this paper, we report a special type of IC flash called "downward positive IC (+IC) flash" which is initiated at high altitudes (mainly above 12 km) and whose initial negative leaders do not propagate upward. Three‐dimensional location results of three downward +IC flashes are described in detail. It is demonstrated that downward +IC flashes start with positive leaders propagating downward with speeds on the order of 104 m/s and negative leaders propagating horizontally for only a short distance. Downward +IC flashes are produced in thunderstorms with deep convective updrafts (radar echoes of cloud tops typically higher than 14 km). The charge structure responsible for downward +IC flashes is inferred to be a positive dipole including a negative charge region at a normal altitude (near the −10 °C isotherm) and an upper positive charge region at a relatively high altitude (usually above the −50 °C isotherm), with downward +IC flashes likely initiated from the upper positive charge region. Further, lightning flashes in a thunderstorm producing a large number of downward +IC flashes are analyzed. Results show that normal IC flashes in this thunderstorm are also initiated at altitudes closer to the upper positive charge region and usually consist of downward positive leaders propagating for longer distances than upward negative leaders. Based on these results, we propose a relationship between the altitude of the upper positive charge region and initiation locations of IC flashes. Plain Language Summary: Intracloud (IC) lightning flashes are normally initiated below 10 km. In this paper, we report a special type of IC flash called the "downward positive IC (+IC) flash" which is initiated at high altitudes (mainly above 12 km). The structure of downward +IC flashes is distinctly different from that of normal IC flashes. Downward +IC flashes are produced in vigorous thunderstorms with cloud tops higher than 14 km. However, downward +IC flashes tend to produce weak radiation in radio frequencies, rendering them difficult to detect. This may be the reason that downward +IC flashes have never been reported before. Key Points: A type of special IC flash initiated at high altitudes (>12 km) called "downward +IC flash" is reported for the first timeDownward +IC flashes are dominated by downward positive leadersDownward +IC flashes are produced in thunderstorms with deep convective updrafts (cloud tops higher than 14 km) [ABSTRACT FROM AUTHOR]

Based on fast electric field waveforms of the Low‐frequency E‐field Detection Array (LFEDA), we introduce the time reversal technique into lightning three‐dimensional location for the first time and propose a new algorithm for the three‐dimensional location of lightning low‐frequency discharges. Without using complex filtering algorithms to remove higher‐frequency component, this method obtains similar results to the newly reported LFEDA refinement algorithm. The new algorithm can obtain finer, more continuous, and richer positioning results with a minimum of four stations, 5‐dB signal‐to‐noise ratio, and 500‐ns time error compared with the low‐frequency signal time of arrival three‐dimensional positioning method. These results indicate that the new algorithm has the advantages of low requirements on the number of stations, certain anti‐interference ability, and low requirements on time accuracy. The standard deviations in the X and Y directions for return strokes of triggered lightning flashes are both approximately 90 m. Plain Language Summary: During the last 20 years, besides the location of return stroke, finer and more accurate positioning of total lightning based on lightning low‐frequency discharge signals can be achieved by using the time of arrival method. The Chinese Academy of Meteorological Sciences developed a lightning Low‐frequency E‐field Detection Array (LFEDA), consisting of ten substations in Conghua, Guangzhou, since 2014, which is capable of determining the three‐dimensional locations of lightning discharge events. With the application of empirical mode decomposition algorithm in the past research of LFEDA, the fine structure of lightning channel can be obtained. This paper proposes a new lightning low‐frequency discharge three‐dimensional location algorithm based on the multistation waveform data of the LFEDA system. This is the first time that the time reversal method has been applied to total lightning three‐dimensional location. This method can obtain accurate lightning three‐dimensional location results without using a complex filtering algorithm. Compared with the time of arrival method, the new algorithm not only can yield positioning results similar to those of the fine positioning algorithm (Fan et al., 2018, https://doi.org/10.1029/2017jd028249) but also has the advantages of low requirements on the number of stations, certain anti‐interference ability, and low requirements on time accuracy. Key Points: A new method based on time reversal technique is proposed for the three‐dimensional location of lightning low‐frequency dischargesThe method has the advantages of low requirements on the number of stations and time accuracy and certain anti‐interference abilityThe method can achieve fine positioning results, and the standard deviations in X and Y directions for return strokes are approximately 90 m [ABSTRACT FROM AUTHOR]

We present in this paper an extension of the guided‐wave M‐component model of Rakov et al. considering the presence of a vertically elevated strike object. The tall object is represented as a lossless, uniform transmission line. Expressions for the current distribution along the channel and along the strike object are derived. Simulation results for the electric field at close (100 m), intermediate (15 km), and far (100 km) distance ranges are presented, considering fast and slow M‐component currents. The results show that, for very tall structures and fast M‐component waves, the presence of a tall strike object can result in a sharp peak superimposed on the M‐component electric field at intermediate and far distance ranges (e.g., 15 and 100 km). At close distances, the electric field of a fast M‐component is characterized by an initial negative excursion followed by a polarity change. It is shown that the presence of the tower results in a decrease of the negative initial excursion of the field. For slow M‐component waveforms or for moderately tall structures, the presence of the tall strike object can be disregarded in the M‐component field calculations. A discussion on the influence of the M‐wave channel height and velocity on the electric fields for fast M‐component currents is also presented. The study suggests a noticeable effect of the M‐wave velocity on the electric fields at all distance ranges. The variations of the wave velocity and channel length affect the time of appearance of the superimposed sharp peak on the electric fields. However, the sharp peak magnitude, which is due to the presence of the tower, is independent of the channel length and wave velocity. It is determined by the injected current and the reflection coefficients from the ground and tower top. Key Points: We propose an extension of the guided‐wave M‐component model of Rakov et al. considering the presence of a vertically elevated strike objectFor very tall structures and fast M‐component waves, the presence of a tall strike object can result in a sharp peak superimposed on the M‐component electric field at intermediate and far distance rangesThe superimposed sharp peak amplitude is independent of the channel length and the wave velocity, while its arrival time is affected by the channel length and the wave velocity [ABSTRACT FROM AUTHOR]

The Asian tropopause aerosol layer (ATAL) has emerged in recent decades with aerosol accumulation near tropopause above Asian Summer Monsoon region. Although ATAL effects on surface and top‐of‐atmosphere (TOA) radiation budgets are well established, the magnitude and variability of ATAL effects on radiative transfer within the tropopause layer remain poorly constrained. Here, we investigate the impacts of various aerosol types and layer structures on clear‐sky shortwave radiative heating in the Asian monsoon tropopause layer using reanalysis products and offline radiative transfer simulations. ATAL effects on shortwave radiative heating based on the Modern‐Era Retrospective Analysis for Research and Applications, version 2 aerosol reanalysis are on the order of 15% of mean clear‐sky radiative heating within the tropopause layer, although discrepancies among recent reanalysis and forecast products suggest that this ratio could be as small as ∼10% or as large as ∼70%. Uncertainties in surface and TOA flux effects are also large, with values spanning one order of magnitude at the TOA. ATAL effects on radiative heating peak between 150 and 80 hPa (360–400 K potential temperature) along the southern flank of the anticyclone. Clear‐sky and all‐sky shortwave heating are at local minima in this vertical range, which is situated between the positive influences of monsoon‐enhanced water vapor and the negative influence of the "ozone valley" in the monsoon lower stratosphere. ATAL effects also extend further toward the west, where diabatic vertical velocities remain upward despite descent in pressure coordinates. Plain Language Summary: Every summer, a layer of polluted air laden with aerosol particles collects above the convective storms of the Asian monsoon as part of a broad upper‐level circulation centered over the Tibetan Plateau. Researchers have developed a working understanding of how the dynamical environment shapes this Asian tropopause aerosol layer (ATAL). The motivating question for this work is: How might the aerosol layer reshape its environment? Aerosols can absorb and scatter sunlight, affecting both the amount of sunlight transmitted through the layer and the magnitude of solar heating within the layer. These effects depend on aerosol species and their vertical distribution within the layer, both of which are highly variable. In this paper, we translate variations and uncertainties in the amount, composition, and vertical distribution of aerosols near the Asian monsoon tropopause into variations and uncertainties in the absorption and scattering of solar radiation by the aerosol layer. We find that aerosols account for a substantial part (10%–70%) of heating by solar radiation near the tropopause in the region of ATAL. The vertical location and horizontal extent of the aerosol effects are distinct from those of other radiative effects. Key Points: The Asian tropopause aerosol layer produces a 10%–70% direct enhancement of clear‐sky shortwave heating above the summer monsoonEffects are largest where shortwave heating is weakest, with similar magnitudes to water vapor and ozone effects near the monsoon tropopauseDiscrepancies across recent aerosol analysis and forecast products cause large uncertainties in aerosol forcing of heating and fluxes [ABSTRACT FROM AUTHOR]

The spatial pattern of intermodel spread of surface temperature (TS‐SPREAD) is similar to the absolute error of modeled surface temperature relative to observations, implying the possibility of using intermodel spread to understand the model biases. The regions with maximum TS‐SPREAD are located in the northern polar (NP) and southern polar (SP) regions, and regions with the large orographic features, such as the Tibetan Plateau (TP). We find: (a) Winter amplification exists in the TS‐SPREAD over both the NP and SP regions, but the maximum TS‐SPREAD over the TP happens during spring and summer with weak seasonality there. (b) Surface energy balance analyses show salient land‐sea contrast in the interlinkage between the physical processes. (c) Over the Arctic Ocean and the Southern Ocean, the maximum spreads of sea‐ice‐induced surface albedo appear during summer when the TS‐SPREADs are the weakest because the effect of surface albedo is offset by the heat storage in the oceans. (d) Through the interseasonal linkage of the heat storage term, i.e., the summer‐storing‐winter‐releasing of oceanic heat content, the summer surface albedo may indirectly contribute to the winter amplification of the TS‐SPREAD over the polar oceans. Such interseasonal linkage of the processes does not exist over the land areas. A method of distinguishing the roles of the local and nonlocal dynamical processes in the contribution of the clear‐sky downward longwave radiation to the TS‐SPREAD is also provided. Plain Language Summary: Understanding the origin of climate model biases is essential to the projection of future climate change, and it is very hard task for the climate modeling community. Here, we show that there exists similarity in the spatial patterns of the intermodel spread, mean absolute errors, and absolute mean errors of surface temperature simulations in climate ensembles. Therefore, we may use the intermodel spread to help understand the mean model biases. We find the regions with maximum surface temperature spread (TS‐SPREAD) are mainly located in the northern polar (NP) and southern polar (SP) regions, and regions with large orographic feature, such as the Tibetan Plateau, indicating the polar and topographic amplifications of TS‐SPREAD in climate models. In the paper, we reveal the process‐chains that lead to the spatial pattern and seasonality of amplified TS‐SPREAD over these regions. We suggest that sea‐ice contributes to the TS‐SPREAD over the NP and SP oceans, not in a direct way, but by its coupling with ocean storage, interseasonal heat release through turbulent fluxes, and also the horizontal heat transport, both across the border of and inside the polar regions. The findings may help climate modelers to improve their models. Key Points: The pattern‐similarity among intermodel spread, mean absolute bias, and absolute mean bias enable us to use the former to understand the latter twoThe interseasonal linkage between surface albedo, heat storage, turbulent fluxes, and dynamical transport causes winter amplification over polar oceansA method is provided to determine the local versus nonlocal contributions to surface downward longwave radiation [ABSTRACT FROM AUTHOR]

The quasi 5‐day wave (Q5DW) with zonal wavenumber 1 is a dominant planetary wave (PW) oscillation in the polar summer mesospheric temperature and polar mesospheric cloud (PMC) fields. In this paper, the Q5DW signal derived from 16 years (2007–2022) of Microwave Limb Sounder temperature observations is used to investigate the role of this PW mode on the onset of PMC seasons in the northern hemisphere (NH). PMC data from the Cloud Imaging and Particle Size (CIPS) instrument during this time indicates that NH PMC season onsets ranged from 15 to 28 May, with earliest onsets in 2013, 2015, 2019, 2020, 2021, and 2022. Except 2013 and 2022, the other four earlier onsets were also characterized by enhanced Q5DW activity. The wave amplification appears to be driven by baroclinic instability arising from the negative meridional gradient of potential vorticity in the high‐latitude summer mesosphere. CIPS data show that when the Q5DW was present at the beginning of the season, clouds formed preferentially in the cold troughs of the wave. We thus propose that the much colder troughs due to enhanced Q5DW activity in mid‐May of 2015, 2019, 2020, and 2021 influenced the timing of PMC onset in these years. While the 11‐year solar cycle, inter‐ and intra‐hemispheric coupling due to gravity wave and PW activity have been shown to contribute to earlier onset of PMC seasons in the NH, our analysis suggests that enhanced Q5DW activity also plays a major role. Plain Language Summary: The quasi 5‐day wave (Q5DW), a wave that takes ∼5 days to travel around a latitude circle, is a dominant planetary scale oscillation in the polar summer mesospheric temperature and polar mesospheric cloud (PMC) fields. We present the first study of the Q5DW impact on the northern hemisphere (NH) PMC season onset. The Q5DW activity is derived from 16 years (2007–2022) of satellite temperature observations. This activity is then compared to the onset of NH PMC seasons determined from the Cloud Imaging and Particle Size (CIPS) observations. The season onsets ranged from 15 to 28 May, with earliest onsets in 2013, 2015, 2019, 2020, 2021, and 2022. Earlier onsets in 2015, 2019, 2020, and 2021 were characterized by increased Q5DW power presumably driven by instability due to large vertical shear in the zonal winds. PMCs are found to form in the cold troughs of the Q5DW. We thus propose that the much colder troughs due to enhanced Q5DW activity in mid‐May of 2015, 2019, 2020, and 2021 influenced the timing of PMC onset in these years. While several other factors contribute to earlier onset of PMC seasons in the NH, our analysis suggests that enhanced Q5DW activity also plays a major role. Key Points: There is year‐to‐year variability in the quasi 5‐day wave (Q5DW) activity in the northern hemisphere summerObservations from 2007 to 2022 indicate that four of the six earliest polar mesospheric cloud (PMC) season onsets are characterized by higher Q5DW activityPMC first form in the longitude sector coincident with the cold trough of the Q5DW [ABSTRACT FROM AUTHOR]

Climate warming causes permafrost degradation that not only leads to the release of greenhouse gases to the atmosphere, but also to soil moisture increases due to ground ice melt. These processes are particularly prevalent in peat‐rich and ice‐rich permafrost regions. Peat is important because of its high organic matter content and soil moisture. Although previous work has focused on the importance of two factors, their precise quantitative impact on permafrost is still not clear. Here we apply the Geophysical Institute Permafrost Laboratory model and sensitivity experiments to quantify the role of organic matter and soil moisture on permafrost, with a case study focused on the northeastern Tibetan Plateau. We verify that organic matter and soil moisture has a cooling effect in the warm season and an insulating effect in the cold season. The average thawing onset was delayed 10 days at 0.05–1.4 m depths, when organic matter content increases from 0% to 90%. Freezing onset occurs slightly earlier. Furthermore, active layer thickness (ALT) decreased by 0.40 m. Soil moisture has similar effect on permafrost as organic matter, but ALT changes have a higher magnitude, decreasing by 0.46 m. The results show that both organic matter and soil moisture have an insulating effect on permafrost. Further, the magnitude of impact is larger as organic matter or soil moisture increase. These results can be helpful in assessing permafrost carbon mitigation with climate change. Plain Language Summary: Permafrost can contain high amounts of organic matter and ground ice, and peat plays an important role in permafrost degradation. Permafrost degrades due to climate warming, which can lead to the release of carbon in the form of greenhouse gases, exacerbating the degradation of permafrost. Additionally, soil moisture also significantly impacts permafrost degradation. However, few studies have estimated the effects of organic matter and soil moisture on permafrost degradation. This paper therefore explores the quantitative effect of organic matter and soil moisture on permafrost through a series of model sensitivity experiments. We find that organic matter and soil moisture both insulate permafrost, cooling it in summer and warming it in winter. These results are important for mitigating the effects of climate change on permafrost and carbon feedbacks. Key Points: The insulating effect of organic matter and soil moisture on permafrost is quantified using model sensitivity experimentsIncreasing organic matter and soil moisture both cool permafrost in summer and warm it in winterThese organic matter and soil moisture feedbacks refine our understanding of permafrost dynamics under climate change [ABSTRACT FROM AUTHOR]

Ensemble clustering analysis was performed to explore the role of the initial hurricane vortex‐scale wind structure in the prediction of the intensification of Hurricane Patricia (2015). Convection‐allowing ensemble forecasts were classified into spin‐down (SPD) and spin‐up (SPU) groups. Specifically, 10 members with an intensification rate >0 m/s and 10 members with an intensification rate <0 m/s for the first 6 hr were defined as the SPD and SPU members. The result showed that the tangential winds outside the inner‐core region in the SPD members were weaker compared to the SPU members. Additionally, the SPD members had a weaker inflow near the surface and a weaker outflow between the heights of 8 and 12 km than the SPU members. The SPU members showed more significant azimuthal asymmetry than the SPD members in the surface, tangential and radial winds. Wavenumber analysis showed that the low wavenumber components dominated the differences between the SPD and SPU members. Numerical experiments were conducted to test the hypothesis generated by the clustering analysis. It was found that the storm's maximum wind speed (MWS) intensified during the first 6 hr of the model forecast if only the low wavenumber structure in the SPU members was included in the initial conditions, whereas it decayed during the first 6 hr if only the low wavenumber structure in the SPD members was included. This result confirms that the low wavenumber structure of the initial wind analyses was important in predicting the intensity changes of Hurricane Patricia (2015). Plain Language Summary: Accurate forecasts of the intensity of tropical cyclones (TCs) are important in both early warning systems and impact assessments. However, the spin‐down (SPD) issue remains a challenge in the operational HWRF model and occurs in many TC cases, especially in the prediction of intense TCs, which can lead to substantial degradation of the short‐term intensity forecast. In this paper, ensemble clustering analysis was performed to explore the role of the initial hurricane vortex‐scale wind structure in the prediction of the intensification of Hurricane Patricia (2015). Convection‐allowing ensemble forecasts were classified into spin‐down (SPD) and spin‐up (SPU) groups. Several statistically significant differences were found in the structure of the initial vortex wind analyses between the SPD and SPU members. Particularly, the low wavenumber components dominated the differences between the SPD and SPU members. Both the wavenumber analysis and numerical experiments suggested that the low wavenumber structure of the initial wind analyses in ensemble members was important in predicting the intensity changes of Hurricane Patricia (2015). These results would be helpful as a way for alleviating the SPD issue in the operational HWRF model system. Key Points: Spin‐up (SPU) members showed more significant azimuthal asymmetry than spin‐down (SPD) members in the initial wind analysesLow wavenumber components dominated the differences between the SPD and SPU membersThe low wavenumber structure of the initial wind analyses was important in predicting the intensity changes of Hurricane Patricia (2015) [ABSTRACT FROM AUTHOR]

The November 2001 Solar Proton Event (SPE) is one of the strongest events in the era of satellite observations. However, no observational case study of this exceptional event's impact on atmospheric chemistry has been reported. In this paper, we use satellite‐based observations from Optical Spectrograph and Infrared Imaging Systems (OSIRIS) to quantify the SPE impact on middle atmospheric O3 in the southern hemisphere during summertime conditions. The results show a relatively modest, yet detectable, O3 depletion in the upper stratosphere and lower mesosphere. Compared to the observations, the Whole Atmosphere Community Climate Model (WACCM‐D) simulates somewhat lower O3 levels before the event but captures well the relative ozone depletion. The largest depletion is seen on November 6th, after the Geostationary Operational Environment Satellite observed the peak proton fluxes. On this day, the O3 depletion was observed and simulated from the pole to 55°S geographic latitude. The daily polar cap (poleward of 60°S geographic latitude) averaged O3 profiles show a maximum depletion of 16.6 ± 2.2% at 1 hPa and 18.8 ± 3.3% at 1.5 hPa altitude, by OSIRIS and WACCM‐D, respectively. After the SPE, an enhancement in NOx is simulated by the results of the model within altitudes of the observation, which is well correlated with the observed and modeled O3 depletion. Challenges related to the detection of SPE impact on O3 in the summer hemisphere are discussed. We find that a careful analysis of simulation results can be essential when isolating the SPE impact from background variation. Plain Language Summary: The 4th of November 2001 solar proton event (SPE) is one of the strongest events in the era of satellite observations. However, no direct satellite‐based observations have been reported for this particular event. Here, we have used observations from the Optical Spectrograph and Infrared Imaging Systems (OSIRIS) instrument, onboard the Odin satellite, to study the impact of this SPE on middle atmospheric ozone in the southern polar region. As OSIRIS is dependent on sunlight to measure ozone, we study the impact in the southern hemisphere during summertime. The observations are compared to a state‐of‐the‐art global climate model that can simulate the atmosphere with meteorological dynamics, coupled with chemistry and radiation such as solar UV and proton events. The results show a modest but detectable upper stratosphere and lower mesospheric ozone depletion in the south polar region. Comparison between observation and model reveals the model has lower ozone levels before the event but captures well the ozone depletion after the SPE. Key Points: We analyze Optical Spectrograph and Infrared Imaging Systems/Odin observations from the southern summer pole and compare them to Whole Atmosphere Community Climate Model simulationsA modest but detectable upper stratospheric and lower mesospheric O3 depletion is seenThe simulated NOx enhancement shows good correlation with the observed and modeled O3 depletion [ABSTRACT FROM AUTHOR]

The Asian summer monsoon (ASM) as a chemical transport system is investigated using a suite of models in preparation for an airborne field campaign over the Western Pacific. Results show that the dynamical process of anticyclone eddy shedding in the upper troposphere rapidly transports convectively uplifted Asian boundary layer air masses to the upper troposphere and lower stratosphere over the Western Pacific. The models show that the transported air masses contain significantly enhanced aerosol loading and a complex chemical mixture of trace gases that are relevant to ozone chemistry. The chemical forecast models consistently predict the occurrence of the shedding events, but the predicted concentrations of transported trace gases and aerosols often differ between models. The airborne measurements to be obtained in the field campaign are expected to help reduce the model uncertainties. Furthermore, the large‐scale seasonal chemical structure of the monsoon system is obtained from modeled carbon monoxide, a tracer of the convective transport of pollutants, which provides a new perspective of the ASM circulation, complementing the dynamical characterization of the monsoon. Plain Language Summary: The Asian summer monsoon has been known as a weather system for centuries, but only in the recent decades has the system been recognized for its importance in atmospheric composition. Monsoon deep convection lofts near surface air to 15–17 km altitudes thus altering the chemical composition of the tropopause layer. The process also sends aerosols and chemically active trace gas species into the stratosphere where they affect climate through their impacts on ozone and aerosol radiative forcing. To understand the monsoon transport process and its impacts on climate system, a large airborne field campaign, the Asian summer monsoon Chemical and Climate Impact Project, was planned. This paper presents a set of results from precampaign model studies. These results serve as the hypotheses for the field investigation and provide guidance for its operational planning. Key Points: This model study is conducted in preparation for an airborne field campaign investigating the Asian monsoon transportResult shows that eastward eddy shedding of the anticyclone significantly alters upper tropospheric composition over the Western PacificCO seasonal distribution provides a chemical perspective of the monsoon system and sheds new light on monsoon dynamics and circulation [ABSTRACT FROM AUTHOR]

The Community Radiative Transfer Model (CRTM) is a fast model that requires bulk optical properties of hydrometeors in the form of lookup tables to simulate all‐sky satellite radiances. Current cloud scattering lookup tables of CRTM were generated using the Mie‐Lorenz theory thus assuming spherical shapes for all frozen habits, while actual clouds contain frozen hydrometeors with different shapes. The Discrete Dipole Approximation (DDA) technique is an effective technique for simulating the optical properties of non‐spherical hydrometeors in the microwave region. This paper discusses the implementation and validation of a comprehensive DDA cloud scattering database into CRTM for the microwave frequencies. The original DDA database assumes total random orientation in the calculation of single scattering properties. The mass scattering parameters required by CRTM were then computed from single scattering properties and water content dependent particle size distributions. The new lookup tables eliminate the requirement for providing the effective radius as input to CRTM by using the cloud water content for the mass dimension. A collocated dataset of short‐term forecasts from Integrated Forecast System of the European Center for Medium‐Range Weather Forecasts and satellite microwave data was used for the evaluation of results. The results overall showed that the DDA lookup tables, in comparison with the Mie tables, greatly reduce the differences among simulated and observed values. The Mie lookup tables especially introduce excessive scattering for the channels operating below 90 GHz and low scattering for the channels above 90 GHz. Plain Language Summary: Radiative transfer (RT) models have a wide range of applications in remote sensing, satellite data calibration, instrument design, and weather forecasts. Although, the clear‐sky simulations conducted by the RT models are relatively accurate, the accuracy of these models for simulating all‐sky observations remains limited. One of the main reasons for inaccuracies in all‐sky simulations is known to be the scattering databases used to calculate the optical properties of different cloud hydrometeors. We implemented and evaluated a large scattering database, computed using the Discrete Dipole Approximation (DDA) technique, into the Community Radiative Transfer Model (CRTM). The results showed that the simulations conducted using the DDA database are much more accurate than the corresponding simulations conducted using the Mie scattering lookup tables which assumes spherical particles for all hydrometeors. Key Points: The cloud scattering lookup tables of Community Radiative Transfer Model (CRTM) discussed and documentedA new scattering database generated using the Discrete Dipole Approximation (DDA) implemented into CRTMThe scattering parameters computed using the DDA technique perform considerably better than Mie coefficients for microwave frequencies [ABSTRACT FROM AUTHOR]

Lower atmospheric gravity waves (GWs) can significantly impact waves in the middle and upper atmospheres and are vital for turbulence generation. This paper puts the spotlight on the spatial–temporal variability of tropospheric GW total energy (ET) and its potential sources above four regions of interest (ROIs) gathered from high‐resolution radiosonde observations from the China Radiosonde Network during the years 2016–2019. The seasonality of ET above four ROIs shows different characteristics and is dependent on latitudes and underlying terrains, reaching its maximum identified in the winter at middle latitudes. Interestingly, the annual cycles of the maximal ET shift from 35°N in October to 25°N in March of the next year, triggered by the shift in the winter subtropical jet. Based on the random forests regressor, the jet stream between 200 and 125 hPa likely serves as the primary source for the observed GWs above the ROIs with low and middle latitudes, with relative contributions of around 60%. However, the Kelvin–Helmholtz instability between 800 and 125 hPa could be the most recognized source of GWs and contributes around 68.4% to the observed energy. During the rainy season, the ET under scenarios of convective precipitation is around 20% larger than the other. As well, as the near‐surface or low‐level wind interacts with a mountain barrier over the Tibetan Plateau region, 12.4% of the observed ET is attributed to the strength of the low‐level wind. Plain Language Summary: The gravity wave (GW) is one of the most important waves in the atmosphere and acts as a triggering source to turbulence. However, the tropospheric GWs in the context of China has seldomly been investigated by using high‐resolution radiosonde data set. This analysis shows that the GW total energy exhibit obvious seasonal various at low and middle latitudes, with maximal identified in the winter and minimal in the summer. The jet stream in the upper troposphere is the most important source for GW at low and middle latitudes and gives rise to a southward propagation of the maximal GW energy in cold season. In the summer of southern China, the convective precipitation could contribute to the enhancement of GW energy. In addition, 12.4% of the observed GW energy is attributed to the strength of the low‐level wind over the Tibetan Plateau. Key Points: Jet stream is the dominant source for gravity waves (GWs) at low and middle latitudes and triggers southward movement of GW energy core during cold seasonsOver the Tibetan Plateau, Kelvin–Helmholtz instabilities and terrain‐induced flows contribute to the intensive GW activitiesDuring the summertime of southern China, convective precipitation could contribute to the enhancement of energy of about 20% [ABSTRACT FROM AUTHOR]

The study is devoted to the analysis of geomagnetic field disturbances and the response of the Schumann resonance (SR) during the eruption of the Tonga volcano in 2022. The data on geomagnetic field variations at distances from 800 to 15,000 km from the volcano according to the INTERMAGNET network and parameters of SR signals recorded at Mikhnevo Observatory in Russia were used. The source of global geomagnetic disturbances are acoustic–gravity waves (AGWs), which caused changes in ionospheric conductivity, values of ionospheric currents, and the geomagnetic field. The propagation velocity of magnetic disturbances 263 ± 5 m/s, corresponding to the AGWs velocity, was determined and an independent estimate of the time of the eruption phase that caused the generation of the atmospheric wave (4:14 ± 10 UT) was obtained. A new method of processing the results of measurements of SR disturbance with a time resolution of 5 min instead of the usual 10–15 min allowed not only to detect but also to study this phenomenon in detail. The peculiarities of signals related to the number and energy of lightning discharges were revealed. Synchronous measurements of SR signals and geomagnetic field variations in a single observatory for the first time allowed to obtain an independent estimate of the eruption time and the electromagnetic disturbance propagation rate. Plain Language Summary: The eruption of the Tonga volcano on 15 January 2022 caused global disturbances in the geomagnetic field and Schumann resonances. The paper shows that the source of disturbance of Schumann resonances during the eruption was increased thunderstorm activity in the volcanic cloud. Disturbances in the geomagnetic field are caused by acoustic‐gravity waves resulting from the eruption. A comprehensive analysis of the data made it possible to determine the time of the beginning of the eruption. Key Points: The eruption of the Hunga Tonga‐Hunga Haapai volcano in January 2021 caused global atmospheric and electromagnetic perturbationsTime of geomagnetic disturbances at distances 800–16,000 km from volcano showed the velocity of their propagation 263 m/s typical for acoustic–gravity wavesThe time difference between geomagnetic disturbance and Schumann resonance response at one point gives an independent estimate of their propagation velocity [ABSTRACT FROM AUTHOR]

Non‐hydrostatic km‐scale weather and climate models show significant improvements in simulating clouds and precipitation, especially of convective nature. However, even km‐scale models need to parameterize some physical processes and are thus subject to the corresponding parameter uncertainty. Systematic calibration has the advantage of improving model performance with transparency and reproducibility, thus benefiting model intercomparison projects, process studies, and climate‐change scenario simulations. In this paper, the regional atmospheric climate model COSMO v6 is systematically calibrated over the Tropical South Atlantic. First, the parameters' sensitivities are evaluated with respect to a set of validation fields. Five of the most sensitive parameters are chosen for calibration. The objective calibration then closely follows a methodology previously used for regional climate simulations. This includes simulations considering the interaction of all pairs of parameters, and the exploitation of a quadratic‐form metamodel to emulate the simulations. In the current set‐up with 5 parameters, 51 simulations are required to build the metamodel. The model is calibrated for the year 2016 and validated in two different years using slightly different model setups (domain and resolution). Both years demonstrate significant improvements, in particular for outgoing shortwave radiation, with reductions of the bias by a factor of 3–4. The results thus show that parameter calibration is a useful and efficient tool for model improvement. Calibrating over a larger domain might help to further improve the overall performance, but could potentially also lead to compromises among different regions and variables, and require more computational resources. Key Points: A systematic calibration method is applied to improve the performance of a km‐resolution regional climate model over the tropical AtlanticCloud‐related model performance at the km‐scale is significantly improved through systematic calibrationThe calibrated parameter setting is robust among different years [ABSTRACT FROM AUTHOR]

As a result of their important role in weather and the global hydrological cycle, understanding atmospheric rivers' (ARs) connection to synoptic‐scale climate patterns and atmospheric dynamics has become increasingly important. In addition to case studies of two extreme AR events, we produce a December climatology of the three‐dimensional structure of water vapor and O3 (ozone) distributions associated with ARs in the northeastern Pacific from 2004 to 2014 using MERRA‐2 reanalysis products. Results show that positive O3 anomalies reside in dry intrusions of stratospheric air due to stratosphere‐to‐troposphere transport (STT) behind the intense water vapor transport of the AR. In composites, we find increased excesses of O3 concentration, as well as in the total O3 flux within the dry intrusions, with increased AR strength. We find that STT O3 flux associated with ARs over the NE Pacific accounts for up to 13% of total Northern Hemisphere STT O3 flux in December, and extrapolation indicates that AR‐associated dry intrusions may account for as much as 32% of total NH STT O3 flux. This study quantifies STT of O3 in connection with ARs for the first time and improves estimates of tropospheric ozone concentration due to STT in the identification of this correlation. In light of predictions that ARs will become more intense and/or frequent with climate change, quantifying AR‐related STT O3 flux is especially valuable for future radiative forcing calculations. Plain Language Summary: Long filaments of rapidly moving water vapor in the atmosphere, known as atmospheric rivers (ARs), play a vital role in the Earth's water cycle. Because of this, research continues to expand into ARs' relationship with large‐scale climate patterns. In this paper, we use data from the Modern Era Retrospective analysis for Research Applications to examine several extreme ARs that made landfall on the U.S. West Coast and their relationship to the transport of ozone from the stratosphere to the troposphere. We then combine 11 years of December AR and ozone data in order to study the average trend of ozone transport in connection with ARs. We quantify the AR‐related ozone transport for the first time, and we find ARs with more intense water vapor transport result in the transport of higher concentrations of ozone. Quantifying ozone transport into the troposphere in connection with ARs is important as ARs may become more intense and/or more frequent with climate change, and ozone in the troposphere has consequences for the greenhouse effect. Key Points: Case studies and December climatology using MERRA‐2 reveal positive tropospheric ozone anomalies within dry intrusions associated with ARsAverage excess ozone concentrations are 10–13 ppbv at 400 hPa, and are even greater for increasing intensity of ARsSTT of ozone associated with ARs in the NE Pacific may account for (13 ± 2)% of the total December Northern Hemisphere STT ozone flux [ABSTRACT FROM AUTHOR]

The physicochemical properties and origins of atmospheric aerosols in the Tibetan Plateau (TP) region are a research topic of great interest, but an in‐depth understanding of this topic is challenging, partially due to a lack of intensive in situ observations. Thus, a field campaign was conducted over Yadong, a remote area on the south slope of the TP from June 11 to 31 August 2021. The aerosol loading was low, with a black carbon mass concentration of 147.4 ± 98.4 ng·m−3. Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm) and increased from 450 to 700 nm wavelength. Organic matter (OM) accounting for 69.6% of the total aerosol mass and relatively high secondary organic carbon ratios, highlighting the importance of secondary formation. An interesting phenomenon observed was that the evolution of aerosols was mainly characterized by diurnal variation, which could not be explained by large‐scale atmospheric processes such as Indian summer monsoon. Instead, it was found that regional mountain‐valley winds between the Himalayas and South Asia transported polluted air masses toward the TP, especially in the afternoon when regional valley wind are expected to be the strongest and the boundary layer in South Asia is deepest. Additionally, daytime local valley wind further elevated these aerosols to higher altitudes on the TP. This paper provides insights into the transport mechanisms of aerosols from South Asia to the TP. These findings are of great importance since aerosols exhibit significant diurnal variations in the TP region. Plain Language Summary: Previous studies focused on the analysis of the physical or chemical properties of aerosols on the Tibetan Plateau, but this study provides a comprehensive examination of both. The findings reveal that aerosols on the southern slope of the Tibetan Plateau exhibit strong absorption efficiency. Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm), which may be attributed to aerosol secondary generation and coating. Finally, the mechanism of pollutant transport from South Asia to the Tibetan Plateau was analyzed relies on site observations, satellite, and reanalysis data to highlight the link between diurnal variations of pollutants and transport mechanism. The specific transport mechanism be understood uniformly across different scales, including Indian summer monsoon, regional mountain‐valley winds between the Himalayas and South Asia, and local mountain‐valley winds circulation. Key Points: Aerosol single‐scattering albedo was low (0.73 ± 0.11 at 550 nm) and secondary organic matter was the major aerosol componentThe evolution of aerosols was mainly characterized by diurnal variation that was related to transport mechanism over YadongThe Himalayas‐South Asia regional mountain‐valley winds combined with local mountain‐valley winds transport aerosols to the Tibetan Plateau [ABSTRACT FROM AUTHOR]

Most tropical cyclone (TC) forecasting centers have implemented a probabilistic circle to represent track uncertainty at a specified lead time. Recent studies suggest that probability ellipses constructed from ensemble prediction systems can convey the anisotropy of track predictability. In this study, a new probability ellipse model is developed to interpret the extent of forward speed and heading uncertainties in ensemble forecasts by selecting an equal proportion of members in the along‐ and cross‐track directions. This method is validated using the 2019–2021 western North Pacific (WNP) TC track forecasts from the ensemble predictions of the European Centre for Medium‐Range Weather Forecasts, the United States National Centers for Environmental Prediction, and the Korea Meteorological Administration. When the proportion of ensemble members in the ellipse is set to 70%, more than one‐half (50.0%–73.6%) of the forecasts, depending on the lead time, indicate reduced area compared with that of the circle. The mean areas of the probability ellipses are 4.9%, 7.0%, 10.0%, and 11.5% smaller than those of the circle in 48‐, 72‐, 96‐, and 120‐hr forecasts, respectively. The forward speed shows greater uncertainty than the heading, as evidenced by the along‐track radii being larger than the cross‐track counterpart in ∼60% of the samples, regardless of the lead time. In addition, the regional distribution of the along‐track/cross‐track ratio in the probability ellipses can explain the dominant direction of the track error in a particular location. The proposed probability ellipse shows potential for application in operational TC track predictions. Plain Language Summary: Operational tropical cyclone (TC) forecasting centers usually represent the uncertainty of a TC track forecast with a circle, namely the probabilistic circle. In this paper, the circle is generalized to a probability ellipse directly using the output of ensemble prediction systems. The key to the new ellipse is that an equal proportion of ensemble members are selected in the along‐ and cross‐track directions to determine the two elliptical radii. This probability ellipse is smaller in size than the circle when representing the same level of uncertainty. The eccentric property of the probability ellipse allows for easy interpretation of the direction with larger ensemble‐forecast uncertainty. Such results can aid in operational TC track predictions and subsequent implementation of preventive measures. Key Points: The proposed probability ellipse explicitly shows the uncertainty of ensemble forecast tracks in the along‐ and cross‐track directionsThe probability ellipse is capable of explaining the dominant direction of error in track forecastsRegional distributions of uncertainty and error resemble each other in terms of magnitude and direction [ABSTRACT FROM AUTHOR]

We conduct a global assessment of the spatial heterogeneity of cloud phase within the temperature range where liquid and ice can coexist. Single‐shot Cloud‐Aerosol Lidar with Orthogonal Polarization lidar retrievals are used to examine cloud phase at scales as fine as 333 m, and horizontal heterogeneity is quantified according to the frequency of switches between liquid and ice along the satellite's path. In the global mean, heterogeneity is greatest between −15 and −4°C with a peak at −5°C, when small patches of ice are prevalent within liquid‐dominated clouds. Heterogeneity "hot spots" are typically found over the extratropical continents, whereas phase is relatively homogeneous over the Southern Ocean and the eastern subtropical ocean basins, where supercooled liquid clouds dominate. Even at a fixed temperature, heterogeneity undergoes a pronounced annual cycle that, in most places, consists of a minimum during autumn or winter and a maximum during spring or summer. Based on this spatial and temporal variability, it is hypothesized that heterogeneity is affected by the availability of ice nucleating particles. These results can be used to improve the representation of subgrid‐scale heterogeneity in general circulation models, which has the potential to reduce longstanding model biases in cloud phase partitioning and radiative fluxes. Plain Language Summary: At temperatures where ice and liquid can coexist within clouds, climate models tend to produce too much ice and too little liquid compared to satellite observations. This bias is likely caused by the assumption that liquid and ice are uniformly mixed, which results in the rapid conversion of liquid to ice for thermodynamic reasons. To reduce this bias, models need to account for the spatial heterogeneity ("patchiness") of liquid and ice that exists in the real atmosphere. The goal of this paper is to quantify this spatial heterogeneity using satellite‐based lidar observations of cloud phase. We find small pockets of ice in liquid‐dominated clouds to be more common than small pockets of liquid in ice‐dominated clouds. The greatest heterogeneity is found over the midlatitude continents, whereas phase is relatively uniform over the Southern Ocean and other maritime regions with extensive low cloud cover. In the mid and high latitudes, cloud phase tends to be more heterogeneous during spring and summer and more homogeneous during autumn and winter. These results can be used in the future to improve model representations of the thermodynamic processes responsible for biases in cloud phase. Key Points: Cloud phase heterogeneity is greatest at −5°C, when small ice patches form in majority‐liquid cloudsCloud phase is relatively homogeneous over the Southern Ocean and heterogeneous over the northern continentsFor a fixed temperature, extratropical phase heterogeneity is generally greatest during local spring and summer [ABSTRACT FROM AUTHOR]

Arctic cyclone activity is an important component of the local climate, and the frequent occurrence of extreme summer storms has raised widespread scientific interest. In this paper, we investigated the distinctive structural characteristics of intense summer Arctic cyclones by utilizing ERA‐Interim reanalysis data and employing a deep learning algorithm for cyclone detection. We found that the northern edge of Eurasia (i.e., the marginal ice zone (MIZ)) and the Alpha Ridge of Arctic Ocean (AR, i.e. central Arctic) are the two most active regions for intense Arctic cyclone activities in summer (from June to September). However, the surface conditions and coupling frequency between surface cyclone and tropopause polar vortices (TPVs) are distinct over these two regions. By further analysis of 100 intense cyclone activities in these two areas, respectively, we found that cyclones in MIZ are often smaller in size but higher in intensity at their maximum intensity, and their life cycles are generally shorter. MIZ cyclones are typically accompanied by a large Eady growth rate and frontal structure in the lower troposphere and their intensification primarily attributed to the thermal‐baroclinic process. In contrast, cyclones in AR are more frequently associated with higher potential vorticity (PV) values and pronounced PV downward intrusion from the stratosphere, as well as notable "upper warm‐lower cold" structures. The downward intrusion of TPVs and stratosphere vortices contribute to a decrease in the upper and column air mass deficit, leading to the intensification of surface Arctic cyclones in these regions. Plain Language Summary: In this study, we researched intense summer storms in the Arctic. We found that there are two main areas where these storms occur: the marginal ice zone (MIZ) near Eurasia and the Alpha Ridge (AR) in the central Arctic. However, storms in these two areas have different characteristics. In the MIZ, the storms are smaller but stronger, and they do not last as long. They are mainly driven by instability in the lower troposphere. On the other hand, the storms in AR respond more to the downward intrusion of potential vorticity from the stratosphere. These storms have a unique structure where the upper air is warmer than their surroundings, and the lower air is colder than their surroundings, especially in AR. This structure makes them more intense and longer‐lasting. Exploring these differences helps us understand how Arctic storms work, and how they might be affected by climate change. Key Points: Both the marginal ice zone (MIZ) and Alpha Ridge exhibit active summer Arctic cyclone activities, especially for intense stormsIn the MIZ, baroclinic instability plays a more prominent role in the intensification and maintenance of cyclonesCyclones in Alpha Ridge are more commonly accompanied by potential vorticity downward intrusion, and "upper warm‐lower cold" structures [ABSTRACT FROM AUTHOR]

This study explores the impact of rising CO2 levels on the Atlantic meridional overturning circulation's (AMOC) interdecadal variability within the context of the Last Glacial Maximum (LGM) background climate. Under heightened CO2 concentrations, the AMOC interdecadal variability intensifies dramatically, which is very different from the future warming case that shows a weakening of AMOC interdecadal variability in response to increased CO2 concentration. This unexpected phenomenon primarily results from the extensive retreat of sea ice, which exposes a larger portion of the ocean surface to efficiently feel the heat flux fluctuations from atmospheric processes. These findings underscore the significance of background climate conditions in shaping AMOC responses to increased CO2 and emphasize the necessity of considering these nuances to develop a more accurate understanding of AMOC dynamics in an evolving climate. Plain Language Summary: The Atlantic meridional overturning circulation (AMOC) is an important component of the Earth system, and its interdecadal variability is predicted to be significantly weakened under future warming scenarios. In this paper, we analyze the response of AMOC interdecadal variability to rising CO2 levels under the background of the Last Glacial Maximum (LGM) and find that the AMOC interdecadal variability is intensified under increased CO2, which is totally different from its response at the background of modern climate. Analyses suggest that this unexpected result is mainly caused by dramatic sea ice retreat, which exposes much seawater to efficiently receive large fluctuations of heat flux from atmospheric forcing. The findings reveal that the response of AMOC to increased CO2 and relevant dominant mechanism differs significantly under different climate conditions. Key Points: The Atlantic meridional overturning circulation (AMOC) interdecadal variability is intensified with increased CO2 under the Last Glacial Maximum (LGM) background climate, diverging from that in future warmingThe intensified AMOC variability cannot be explained by ocean dynamics as shown in future warming casesLarge sea ice retreat drives the intensification of AMOC interdecadal variability under the LGM warming [ABSTRACT FROM AUTHOR]

More and more optical records have exhibited that multiple upward leaders (MULs) occur frequently on a building in the flash attachment process. An interesting issue is why a building can continue to launch upward leader (UL) after the first one appears. This phenomenon is analyzed in the present paper. Considering the influence of the leader behaviors on the ambient electric field, an improved 3‐D fine‐resolution lightning attachment model with MULs is established to simulate cloud‐to‐ground flash events with diverse leader spatial morphologies. The simulation results show that MULs may initiate almost simultaneously or with an obvious delay and the variation range of UL length is large. From this, the flash events of lightning terminating on a building are divided into four scenarios and each scenario is analyzed. It was found that the spatial location of downward leader, the length and propagation direction of the first UL and the time interval from the inception of the first UL to final jump significantly affect the electric fields at top corners of building and further affect the inception of the second UL. Based on qualitative analysis, four factors are proposed to explain why the above four scenarios happen. Plain Language Summary: This research focuses on understanding the process of cloud‐to‐ground (CG) lightning, which can cause significant harm to society. Specifically, the study investigates the initiation of multiple upward leaders in the CG lightning process. By considering the impact of lightning leader behaviors on the surrounding electric field, the researchers develop an improved lightning attachment model. Using this model, we simulate the development of leaders and identify factors that explain why one or more leaders originate from an isolated building. The results highlight the importance of the location of the lightning, the characteristics of the first upward leader, and the timing of the lightning strike in influencing the initiation of multiple upward leaders. Future studies will explore CG lightning within groups of buildings, contributing to our understanding of this phenomenon and providing insights for protecting buildings from lightning strikes. Key Points: An improved 3‐D fine‐resolution stochastic discharge model is developedThe spatial location of lightning, as well as the length and propagation direction of the first upward leader, has an impact on the initiation of multiple upward leadersThe time interval between the inception of the first upward leader and the final jump affects the initiation of multiple upward leaders [ABSTRACT FROM AUTHOR]

Our basic knowledge of downward positive lightning leaders is incomplete due to their rarity and limited ability of VHF mapping systems to image positive streamers. Here, using high‐speed optical records and wideband electric field and magnetic field derivative signatures, we examine in detail the development of a descending positive leader, which extended intermittently via alternating branching at altitudes of 4.2 to 1.9 km and involved luminosity transients separated by millisecond‐scale quiet intervals. We show that the transients (a) are mostly initiated in previously created but already decayed branches, at a distance of the order of 100 m above the branch lower extremity, (b) extend bidirectionally with negative charge moving up, (c) establish a temporary (1 ms or so) steady‐current connection to the negative part of the overall bidirectional leader tree, and (d) exhibit brightening accompanied by new breakdowns at the positive leader end. One of the transients unexpectedly resulted in a negative cloud‐to‐ground discharge. Both positive and negative ends of the transients extended at speeds of 106–107 m/s, while the overall positive leader extension speed was as low as 103–104 m/s. Wideband electric field signatures of the transients were similar to K‐changes, with their millisecond‐ and microsecond‐scale features being associated with the steady current and new breakdowns, respectively. For transients with both ends visible in our optical records, charge transfers and average currents were estimated to be typically a few hundreds of millicoulombs and some hundreds of amperes, respectively. Plain Language Summary: Our knowledge of downward positive lightning is very limited. Positive lightning constitutes only about 5% of the global lightning activity, but it causes the most severe damage to various objects and systems, as well as most transient luminous events in the mesosphere. The leader processes in positive lightning remain a mystery and are widely debated in the atmospheric electricity community. In this paper, we present two new findings on propagation mechanisms of branched downward positive leader: (a) its ability to produce an opposite‐polarity (negative) lightning discharge to ground and (b) its unusual mode of propagation involving bidirectional transients, which temporarily reactivate individual leader branches and facilitate their alternating extension. Key Points: Branched positive leader extending at an average speed of 103–104 m/s resulted in a three‐stroke negative cloud‐to‐ground flashPositive leader extension involved bidirectional transients, moving negative charge up, separated by millisecond‐scale quiet intervalsElectric field signatures of the transients are similar to K‐changes and are associated with steady currents and new breakdowns at far end [ABSTRACT FROM AUTHOR]

In this paper, we present XStorm, a gamma ray spectrometer developed to detect gamma ray glows and terrestrial gamma ray flashes (TGFs) in close proximity. Measurements are mostly planned to take place on balloon campaigns but also on the ground using bigger detectors. The main aim in developing XStorm is to perform new in situ and close proximity measurements of those events to improve the understanding of the physical processes involved. For that, we ensured XStorm reached performances adapted to glow and TGF detections. It detects photons with energy between ∼400 keV and ∼20 MeV. Detected particles are timetagged with a 600 ns precision with respect to UTC. Using two types of scintillator, Bismuth Germanium Oxide and EJ‐276 plastic associated with SiPMs, the instrument is able to discriminate three types of particles involved in those events: photons, neutrons, and electrons. The behavior of the detector under high particle fluxes has been quantified through ground testing using a pulse generator. A triggered detection system has been developed, with different thresholds depending on the target of study. First measurements have been carried out with test flights in fair weather conditions and are presented here. Estimations of the configurations in which a gamma ray glow can be detected by XStorm and of the number of TGFs that could be detected in specific campaigns are also addressed. Plain Language Summary: Terrestrial gamma ray flashes (TGFs) are bursts of high‐energy photons generated in thunderstorms in less than 100 μs, whereas gamma ray glows are enhancement of the high‐energy radiation background in thunderstorms, lasting from seconds to minutes. We present a gamma ray spectrometer, XStorm, designed to detect terrestrial gamma ray flashes (TGFs) and gamma ray glows in close proximity. It is composed of two scintillators of different kinds to allow the detection of TGF and gamma ray glow photons (energies between 400 keV and 20 MeV, with a time precision of 600 ns UTC). XStorm measurements are mainly planned to take place on board balloons, but can also be performed at ground level using bigger scintillators. XStorm is able to discriminate photons, electrons and neutrons, that are particle types involved in TGFs. We show the first measurements in fair weather and configurations allowing the detection of gamma ray glows. We estimate that XStorm will detect ∼0.5 TGF on average over one balloon flight of Stratéole‐2 campaign presented in the scientific objectives. Key Points: Development of a gamma ray spectrometer to detect gamma ray glows and terrestrial gamma ray flashes (TGFs), able to discriminate photons, electrons, and neutronsResults from balloon test flights performed in fair weather conditions, detecting the background radiation level as a function of altitudeEstimation of the detectability of gamma ray glows and TGFs as a function of altitude with XStorm [ABSTRACT FROM AUTHOR]

The role of free passage distance (FPD: the distance between the avalanche region and surface detectors) in influencing the relative numbers of energetic electrons and gamma rays in Thunderstorm Ground Enhancements (TGEs) is reconsidered and focuses on the contrast between long (>100 m) versus short (<100 m) FPDs, respectively. Estimates of FPD are based on information from published balloon soundings of the electric field, from published profiles of radar reflectivity in TGEs, and from analyses of Japan winter storms. All these data sources support typical values of FPD >100 m. Neither the shortcomings of present particle detectors in distinguishing electrons from gamma rays, nor the dominance of gamma rays over electrons, are sufficient evidence to deny the robust presence of Compton electrons at FDP values greater than 100 m that have also been shown in earlier simulations as well as the present Comment. Problems with having sustained electric fields of breakeven magnitude within 100 m of the Earth's surface (in relatively rare TGEs) are identified. The resolution of these problems, and the prominent nocturnal presence of these rare events, may possibly be explained by the descent of a strong field region in a collapsing storm, and by a low cloud base that intercepts and immobilizes fast corona ions, thereby preserving the intense electric field. Plain Language Summary: Thunderstorms are capable of accelerating electrons to large energy by a process called electron runaway. This process is often confined to the cold portion of the thunderstorm at higher altitude where ice particles are available to separate electric charge to produce the necessary electric field, and where so‐called avalanche electrons are present. As a result, the high field region in the storm is removed from the ground where measurements of energetic radiation are usually undertaken to diagnose electron acceleration aloft. Gamma rays are produced when the energetic electrons are decelerated in coming in contact with heavy nuclei in a process called bremsstrahlung. Electrons unaided by strong field have short range in the atmosphere: tens of meters and less, whereas gamma rays have larger range (hundreds of meters). Accordingly, energetic electrons cannot be expected far (>200 m) below the high field region. One possible scenario for reducing this gap is the descent of strong field to near cloud base in a collapsing storm and the protection of field dissipation by the capture of small corona ions by cloud droplets. Evidence from several research areas in the literature is used to support the arguments in this paper. Key Points: Energetic Compton electrons are an inevitable accompaniment of the gamma ray flux of Thunderstorm Ground Enhancements (TGEs) but in numbers too small to be readily distinguished from the gamma rays with typical detectorsThe observations of avalanche electrons in TGEs is surprising, given the small free passage distance (FPD) (<50–100 m) requiredOne suggested scenario for creating small FPD is the lowering of negative charge in storm collapse and the capture of fast corona ions by cloud droplets [ABSTRACT FROM AUTHOR]

The sensitivity of tropical cyclone (TC) intensification to its inner size in a sheared environment is investigated in this study. Previous research indicated that TCs with smaller sizes spin up more quickly in a quiescent environment. In contrast, our idealized numerical simulations show that TCs with larger inner‐core sizes experience faster growth within a certain size range under the vertical wind shear (VWS) because stronger upper‐level outflows are established quickly for larger TCs. The presence of strong outflow diminishes the impact of VWS, causing the TC re‐alignment. In more detail, the stronger outflow locally reduces the shear, allowing the convective asymmetry to propagate to the upshear side and migrate inward toward the TC center more rapidly. The upshear convection leads to a stronger outflow and thus a greater blocking effect on the upper‐level wind, effectively reducing the VWS and thus allowing subsequent faster TC growth. Our analysis reveals that the TC re‐alignment at an earlier stage allows for significant differences in surface heat flux (surface latent heat flux [SLHF]) distribution based on size. Larger TCs exhibit larger areas of high SLHF, which create favorable thermodynamic conditions for TC developments. Conversely, smaller vortices have limited SLHF underneath, resulting in a prolonged intensification process. Furthermore, the boundary layer recovery mechanism effectively counteracts the low‐level ventilation pathway imposed by the shear. This mechanism supports the downstream deep convection development on the upshear side. This study presents a new perspective, highlighting that the impact of shear on TCs is contingent upon their sizes upon entering a sheared environment. Plain Language Summary: The paper shows that a tropical cyclone (TC) with a larger inner‐core size experiences rapid intensification in the presence of vertical wind shear (VWS). Our findings indicate that when the TC has a larger inner‐core size, the enhanced inner‐core convection can increase the upper‐level outflow, which helps to resist the upper‐level environmental wind and reduce the VWS. This leads to the TC re‐alignment and allows for faster development. The large‐size TC possesses a larger area of high surface heat flux that provides abundant energy for TC development. This finding emphasizes a new perspective, highlighting that the impact of shear on TC development is contingent upon the size of the TC itself. Key Points: In the presence of vertical wind shear (VWS), tropical cyclone (TC) with a larger size is apt to experience a high intensification rateTC with a larger size quickly develops stronger upper‐level outflow, which helps decrease VWS. This leads to TC re‐alignment and faster developmentThe TC with a larger sizes possesses a larger area of high surface heat flux, favoring the thermodynamic forcing for TC rapid development [ABSTRACT FROM AUTHOR]

Polar stratospheric clouds (PSCs) play a key role in Arctic amplification and stratospheric ozone destruction in polar regions. In this paper, we used the CALIPSO data to analyze the spatiotemporal distribution of Arctic PSCs from 2006 to 2021. We found that Arctic PSCs mainly appear in December, peak in late December and early January, disappearing in late February and early March. PSCs can extend from heights near the tropopause to over 25 km. However, there is the lowest fraction of PSCs in the 2014/2015 winter. This study found that the temperature in the 2014/2015 winter was warmer than the 15‐year average temperature, with the lowest temperature slightly below the PSCs formation temperature of about 5 K. The formation of the Ural blocking high accompanied by the poleward propagation of the planetary wave caused a sudden stratospheric warming (SSW) event on 3 January 2015, during which the warm air entered the polar vortex and divided it into two lobes. Additionally, a reduction in SO2 column mass density before the SSW event resulted PSCs occurring with a frequency of only 0.148 and dissipating rapidly in December. Moreover, the concentration of H2O and HNO3 in the gravitational settling process of PSCs decreased by 20–50%, the reduction of condensation nuclei made PSCs with the highest frequency of 0.074 in February appear briefly and then disappear. The chemical and dynamic analysis of PSCs formation is needed to further understand the spatiotemporal distribution of Arctic PSCs and to better predict future Arctic amplification and ozone destruction. Plain Language Summary: Polar stratospheric clouds (PSCs) influence polar ozone depletion by providing a reaction interface and also influencing surface temperature changes through longwave radiation effects. Previous studies on polar stratospheric clouds mainly focus on the Antarctic, and few studies on the temporal and spatial distribution characteristics of Arctic PSCs over long timescales. Therefore, by studying the spatial and temporal distribution of PSCs in the Arctic, we found that the spatial and temporal distribution of PSCs in the Arctic has obvious interannual variation compared with that in the Antarctic. The stratospheric sudden warming (SSW) events that occur almost every 2 years in the Arctic cause great interannual variations of the Arctic polar vortex and thus affect the distribution of Arctic PSCs. Moreover, there is the least and almost none occurrence of PSCs in the 2014/2015 winter, the chemical and dynamic analysis found that SSW, decrease of SO2, H2O, and HNO3 concentration are not conducive to the formation of PSCs. It is of great significance to study the influencing factors of Arctic PSCs formation and provide a new basis for further prediction of Arctic amplification and ozone destruction. Key Points: The fraction of Arctic polar stratospheric clouds (PSCs) during 2014/2015 winter was the lowest observed in the past 15 yearsThe splitting of polar vortex and the rise in temperature caused by sudden stratospheric warming (SSW) inhibited the formation of PSCsThe decrease in stratospheric sulfur dioxide, nitric acid, and water was unfavorable for the formation of PSCs before and after the SSW [ABSTRACT FROM AUTHOR]

Retraction: Kuo, C., Feldman, D. R., Huang, X., Flanner, M., Yang, P., & Chen, X. (2018). Time‐dependent cryospheric long wave surface emissivity feedback in the Community Earth System Model. Journal of Geophysical Research: Atmospheres, 123, 789–813. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017JD027595. The above article from Journal of Geophysical Research: Atmospheres, published online on 3 January 2018, has been retracted by agreement between the authors; the journal Editor‐in‐Chief, Minghua Zhang; the American Geophysical Union; and Wiley Periodicals LLC. The retraction has been agreed because in the experimental setup of the original paper, surface temperature over the oceans was from the sea‐surface temperatures (SST) in the radiative transfer calculation of the CESM rather than from the correct weighted average of liquid and sea‐ice temperature (TS). This error affects the quantitative results of warmer wintertime Arctic surface temperatures, which were attributed in the original paper to the proposed spectral distribution of surface emissivity. [ABSTRACT FROM AUTHOR]

The Western North Atlantic Ocean (WNAO) is a complex land‐ocean‐atmosphere system that experiences a broad range of atmospheric phenomena, which in turn drive unique aerosol transport pathways, cloud morphologies, and boundary layer variability. This work, Part 2 of a 2‐part paper series, provides an overview of the atmospheric circulation, boundary layer variability, three‐dimensional cloud structure, and precipitation over the WNAO; the companion paper (Part 1) focused on chemical characterization of aerosols, gases, and wet deposition. Seasonal changes in atmospheric circulation and sea surface temperature explain a clear transition in cloud morphologies from small shallow cumulus clouds, convective clouds, and tropical storms in summer, to stratus/stratocumulus and multilayer cloud systems associated with winter storms. Synoptic variability in cloud fields is estimated using satellite‐based weather states, and the role of postfrontal conditions (cold‐air outbreaks) in the development of stratiform clouds is further analyzed. Precipitation is persistent over the ocean, with a regional peak over the Gulf Stream path, where offshore sea surface temperature gradients are large and surface fluxes reach a regional peak. Satellite data show a clear annual cycle in cloud droplet number concentration with maxima (minima) along the coast in winter (summer), suggesting a marked annual cycle in aerosol‐cloud interactions. Compared with satellite cloud retrievals, four climate models qualitatively reproduce the annual cycle in cloud cover and liquid water path, but with large discrepancies across models, especially in the extratropics. The paper concludes with a summary of outstanding issues and recommendations for future work. Key Points: Atmospheric circulation and sea surface temperature drive large seasonal changes in precipitation, surface fluxes, and cloud typesSynoptic activity in winter yields the highest seasonal rain rates, low‐cloud occurrence, and cloud droplet number concentrationsClimate models simulate a wide range of low‐cloud properties, with improved results for models with more sophisticated turbulence schemes [ABSTRACT FROM AUTHOR]

Providing skilful predictions of high‐impact weather up to 2 weeks ahead is on the agenda of international weather centers. Evaluating the capabilities of current numerical systems in predicting past events can bring extremely valuable contributions to the assessment of the information content available today with operational models. In the framework of the activities for the fiftieth anniversary of the extreme precipitation event that occurred in Italy in November 1966, this paper investigates its predictability using state‐of‐the‐art global and regional ensemble simulations. The first goal is to assess if and how many days in advance, this event can be predicted by current European Centre for Medium‐Range Weather Forecasts (ECMWF) global ensembles. A second goal is to evaluate the potential added value of running nested higher‐resolution and convection‐permitting ensembles. It is shown that ECMWF ensembles are able to provide valuable information up to 3 days before the event. Within this forecast range, convection‐permitting simulations can provide more accurate estimations of precipitation maxima. However, the results indicate also a strong underestimation of rainfall amounts with both global and regional models even at short forecast range. To partially explain this shortcoming, we discuss how the scarcity of observations available in 1966 for the analysis process limits the quality of the ensemble initial conditions and we adopt a method to obtain more reliable ensemble forecasts. The paper concludes with a comparison with previous similar works; results indicate a gain in predictability of up to 12 hr with respect to numerical revisitations performed to mark the fortieth anniversary of the event. Key Points: Current state‐of‐the‐art global ensembles are able to provide valuable information up to 3 days before the Arno River flooding event (Italy, November 1966)Convection‐permitting ensembles provide more accurate estimations of precipitation maximaAdvances in numerical modeling occurred in the last 10 years, determine a gain in predictability of up to 12 hr with respect to similar works [ABSTRACT FROM AUTHOR]

Accurate tracking of all components (including core, anvil, and cirrus) of deep convective systems (DCSs) throughout their lifecycle is key to quantifying their impacts on radiative forcing, especially of the anvil and cirrus. Here, a new Full‐tracking Algorithm for Convective Thunderstorm System is developed based on geostationary satellite. It successfully tracks DCSs starting from the initial core to complete dissipation of cirrus detrained from them, and integrates all the related components that split from the initial convective core into a whole DCS. Results show that more than half of the tracked DCSs experience splitting evolutions, with an average of eight sub‐cores during their lifetime. With tracking cirrus generated by DCSs, the lifetime of DCSs is lengthened by up to 10 hr, and their area is enlarged by 16% on average. Generally, long‐lived DCSs have lower cloud top temperature, greater rainfall, and larger area, with more frequent splitting evolutions than short‐lived DCSs. Additionally, DCSs always reach their peaks within 6 hr after initiation regardless of their lifetime. This paper provides a basis for further quantifying the evolution of DCS properties, their impacts on the global radiation budget, and the water cycle in the climate system. Key Points: A novel method is developed to track full components of deep convective systems (DCSs) from their initiation to total cirrus dissipationLifetime of DCSs is extended by up to 10 hr, and their area is enlarged by 16% averagely after continuously tracking their detrained cirrusIntegrated total rainfall amounts are comparably contributed between frequent but small and rare but large DCSs [ABSTRACT FROM AUTHOR]

High concentrations of ozone along the coastline of Lake Michigan are a persistent air quality management challenge. Complementing observations during the 2017 Lake Michigan Ozone Study (LMOS 2017), WRF‐Chem modeling was used to quantify sensitivity of modeled ozone (O3) to anthropogenic nitrogen oxides (NOx) and volatile organic compound (VOC) emissions, including to changes in volatile chemical product (VCP). The daily maximum 8 hr average (MDA8) over the high ozone region of Lake Michigan decreased by 2.7 ppb with exclusion of VCP from the inventory, and was sensitive to both NOx and VOC changes, with greater sensitivity to NOx. Close to urban centers, MDA8 ozone was VOC‐sensitive. Clusters of coastal receptor sites were identified based on similarity in response to emission perturbations, with most clusters being NOx‐sensitive and NOx‐sensitivity increasing with distance from major emission sources. The 2 June 2017 ozone event, which has received considerable focus, is shown to be atypical due to unusually strong and spatially extended VOC‐sensitive behavior. WRF‐Chem integrated reaction rate analysis was used to compute radical termination rates due to NOx (LNOx) and to radical‐radical reactions (LROx). LROx/LNOx and formaldehyde to NO2 ratio (FNR) were shown to be predictive of modeled MDA8 ozone sensitivity, but with variation in predictive power as a function of time of day, which has implications for air quality management use of FNR from geostationary satellites. Plain Language Summary: Surface ozone is an air pollutant of concern due to human health impacts. In locations with elevated ozone concentrations, including coastal regions around Lake Michigan, ozone pollution is managed by controlling emissions of the two classes of chemicals that drive ozone chemistry: volatile organic compounds (VOCs) and nitrogen oxides (NOx). However, due to large reductions in emissions of NOx and VOC over the past 20 years, the leverage that future reductions will have is uncertain. Reductions of 4–5 ppb (∼7%) are needed in several locations, relative to 2017–2019 concentrations, to meet the 2015 ozone standard of 70 ppb. In this paper, we use simulations of atmospheric chemistry and airflow over the Midwestern US to address this issue. By comparing simulations based on different VOC and NOx emissions, we find that reductions in NOx emissions have more influence on ozone than reductions in VOC emissions, except for a small zone downwind of Chicago. On high ozone days over Lake Michigan, a 10% decrease in VOC (NOx) emissions can lower ozone in the key high ozone zone over southern Lake Michigan by 0.4% (0.8%). Volatile chemical products, an uncertain component of emission inventories, are responsible for 2.7 ppb (∼4%) of ozone. Key Points: Outside of a small (85 km) zone downwind of Chicago, ozone concentrations and production near Lake Michigan is generally NOx‐sensitiveOn event days 10% decrease in volatile organic compound emission can lower MDA8 by 0.4% and 10% decrease in nitrogen oxides emission can lower MDA8 by 0.8% over Lake MichiganVolatile chemical product emissions were modeled to produce an average 2.7 ppb ozone increase over the lake [ABSTRACT FROM AUTHOR]

Stable water isotopes are used as a paleothermometer in ice cores for climate reconstructions over the past millennia. The underlying physical processes involved in the isotope‐temperature relation, however, unfold at much shorter timescales. Here, we study the temporary archival of frontal passages in the seasonal Alpine snow cover. We combine five snow profiles sampled in winter 2017 at the Weissfluhjoch with a quantitative snow layer age reconstruction and atmospheric reanalysis data to characterize the circulation and clouds associated with the precipitation producing synoptic‐scale cold and warm fronts. We find that the vertical cloud structure and the air parcels' net cooling during transport leave a distinct imprint in the δ18O and δD vertical profile in the snow. The near‐surface humidity gradient at the moisture source is reflected in the second order isotope parameter deuterium excess. In the cold season, these environmental conditions during cloud formation and at the moisture source are preserved in the snow. In the melt season, significant post‐depositional effects due to wet snow metamorphism, however, leads to an enrichment in heavy isotopes in the snow and a strong smoothing of the initial atmospheric imprint. These findings show that the isotope signal archived in the dry snow cover is strongly modulated by individual weather systems prior to deposition. Major shifts in the upper‐level jet stream and cyclone tracks likely leading to changes in moisture source regions and conditions, could therefore be detectable in the isotope composition of Alpine ice. Plain Language Summary: To obtain information on past climate conditions, the non‐radioactive, heavy versions of the water molecule are often used as paleothermometers in ice cores. However, the processes that determine how this paleothermometer works, act at the weather‐system timescale (days), not the climate timescale (years). In this paper, we illustrate how isotope information from five snow profiles relate to the history of the water in the atmosphere during frontal passages. We show that the meteorological conditions at the evaporative source and in the clouds where the snow crystals are formed, determine the concentration of stable water isotopes in the snow. Transformation processes of the snow's structure, after it has been deposited do not significantly alter the isotope signals in the cold season. However, as soon as melting starts, the heavy water molecules accumulate in the snow, while the lighter ones are washed out. Key Points: Mid‐latitude synoptic fronts leave a distinct isotope signature in the Alpine snow cover that is preserved during the cold seasonThe cloud formation temperature determines the δ18O and δD of the buried snow, and moisture source information is preserved in the deuterium excessPost‐depositional dry metamorphism acts to smooth the snow isotope profile, while wet snow metamorphism leads to an enrichment of the snow [ABSTRACT FROM AUTHOR]

The formation of the Aralkum (Aral Desert), following the severe desiccation of the former Aral Sea since the 1960s, has created what may be regarded as one of the world's most significant anthropogenic dust sources. In this paper, focusing on dust emission and transport patterns from the Aralkum, the dust life‐cycle has been simulated over Central Asia using the aerosol transport model COSMO‐MUSCAT (COnsortium for Small‐scale MOdelling‐MUltiScale Chemistry Aerosol Transport Model), making use of the Global Surface Water data set to take into account the sensitivity to changes in surface water coverage over the region between the 1980s (the "past") and the 2010s (the "present"). Over a case study 1‐year period, the simulated dust emissions from the Aralkum region increased from 14.3 to 27.1 Tg year−1 between the past and present, an increase driven solely by the changes in the surface water environment. Of these simulated modern emissions, 14.5 Tg are driven by westerly winds, indicating that regions downwind to the east may be worst affected by Aralkum dust. However a high degree of interannual variability in the prevailing surface wind patterns ensures that these transport patterns of Aralkum dust do not occur every year. Frequent cloud cover poses substantial challenges for observations of Central Asian dust: in the Aralkum, over two‐thirds of the yearly emissions are emitted under overcast skies, dust which may be impossible to observe using traditional satellite or ground‐based passive remote sensing techniques. Furthermore, it is apparent that the pattern of dust transport from the Aralkum under clear‐sky conditions is not representative of the pattern under all‐sky conditions. Plain Language Summary: Since the 1960s the Central Asian lake that used to be known as the Aral Sea has almost completely dried out, due to human activity. This environmental disaster has created a new desert known as the Aralkum (the "Aral Desert"), which now has a size of 245 km × 245 km across. Dried lakes such as the Aralkum can be very effective sources of wind‐driven atmospheric dust. The soils of the Aralkum are also contaminated with agricultural chemicals from nearby croplands, making the Aralkum a major regional threat to human health. Using an atmospheric computer model, we explore the consequences of the new Aralkum for the patterns of atmospheric dust and their potential impacts in Central Asia. We find that the new Aralkum has contributed an extra 7% per year to the total dust quantity over Central Asia, however due to thick cloud cover over two thirds of this dust from the Aralkum cannot be seen by Earth‐observing satellites. The wind patterns over the Aralkum vary from year to year, so while our simulations predict that most of the Aralkum's dust is transported to the east during the simulation year, during other years plenty more dust will be transported elsewhere. Key Points: The impact of changes in surface water coverage over the Aralkum (the former Aral Sea) for dust emission and transport is investigatedThere is a high degree of interannual variability in the directions of dust‐emitting winds over the AralkumOver two thirds of Aralkum dust activity occurs under thick cloud cover, limiting the possibility of it being observed by satellites [ABSTRACT FROM AUTHOR]

Kostinskiy et al. (2015b), https://doi.org/10.1002/2015GL065620, using a high‐speed infrared (2.5–5.5 μm) camera, discovered the so‐called unusual plasma formations (UPFs) in artificial clouds of charged water droplets. UPFs had complex morphology including both streamer‐like regions and hot channel segments. They were observed both in the presence and in the absence of hot leader channels developing from the grounded plane toward the cloud. In this paper, which is aimed at revealing the genesis of UPFs, we present two UPFs that occurred inside the initial corona streamer burst of positive polarity emitted from the grounded plane, prior to the formation (or in the absence) of associated hot leader channel. These streamer bursts developed at speeds of 5–7 × 105 m/s over 1–1.5 m before entering the optically visible negatively charged cloud and producing UPFs at its periphery. Hot channel segments within UPFs were formed in very short times of the order of 1 μs or less. It is not clear if the UPFs were caused solely by the enhanced electric field near the charged cloud boundary or other factors also played a role. Occurrence of UPFs may be a necessary component of the lightning initiation process. Key Points: Unusual plasma formations (UPFs) can occur inside the initial corona streamer burst, before the development (or in the absence) of hot leader channelUPFs contain hot channel segments that are formed, possibly via the thermal‐ionizational instability, on a time scale of 1 μs or lessUPFs occurred in the vicinity of cloud boundary, where the electric field is highest, as this boundary is penetrated by the streamer burst [ABSTRACT FROM AUTHOR]

According to recent field studies, almost half of the New Particle Formation (NPF) events occur aloft, in a residual layer, near the top of the boundary layer. Therefore, measurements of the meteorological parameters, precursor gas concentrations, and aerosol loadings conducted at the ground level are often not representative of the conditions where the NPFs take place. This paper presents new measurements obtained during the Turbulent Flux Measurements of the Residual Layer Nucleation Particles, conducted at the Southern Great Plains research site. Vertical turbulent fluxes of 3–10 nm‐sized particles were measured using a sonic anemometer and two condensation particle counters with nominal cutoff diameters of ≥ $\ge $3 nm and ≥ $\ge $10 nm mounted at the top of the 10‐m telescoping tower. Aerosol number size distribution (5–300 nm) was determined through the ground‐based Scanning Mobility Particle Sizers. The size selected (15–50 nm) particle hygroscopicity was derived with the Humidified Tandem Differential Mobility Analyzer. The ground level observations were supplemented by vertically‐resolved measurements of horizontal and vertical wind speeds and aerosol backscatter. The data analysis suggests that (a) turbulent flux measurements of 3–10 nm particles can distinguish between near‐surface and residual‐layer small particle events; (b) sub‐50 nm particles had a hygroscopicity value of 0.2, suggesting that organic compounds dominate atmospheric nanoparticle chemical composition at the site; and (c) current methodologies are inadequate for estimating the dry deposition velocity of sub‐10 nm particles because it is not feasible to measure particle concentration very near the surface, in the diffusion sublayer. Plain Language Summary: The atmosphere is filled with microscopic particles, termed "aerosols." Many of these particles are produced through a complex process known as new particle formation or nucleation. As the particle concentration in the atmosphere has been shown to influence Earth's radiative balance and human health, the formation of new particles from the gas phase is a topic of interest for both climate and air quality sciences. Researchers have identified some factors that influence nucleation events, though none of these factors can explain and predict nucleation consistently. There is evidence that roughly half of the nucleation events detected at ground level originate above the surface, where the process is favored by colder temperatures, lower preexisting particle concentrations, and higher relative humidity. Therefore, ground level measurements may not always be representative of the conditions under which nucleation takes place. The inability to distinguish between ground level and elevated nucleation events is contributing to inconsistencies in our understanding of the factors that influence nucleation. Here, we show that vertical turbulent fluxes of 3–10 nm‐sized particles can be used to distinguish between near‐surface and residual‐layer nucleation. We also show that the existing methodology is inadequate for the estimation of particle dry deposition velocity. We believe these findings will help to better represent aerosols in regional and global climate models. Key Points: Near‐surface/residual‐layer particle nucleation events can be identified by positive/negative turbulent fluxes of 3–10 nm sized particlesHygroscopic diameter growth factor measurements show that organics are dominating sub‐50 nm composition at the Southern Great Plains siteThe eddy‐covariance measurements are inadequate for the estimation of sub‐10 nm particle deposition velocity in most environments [ABSTRACT FROM AUTHOR]

The persistent Southern Ocean (SO) shortwave radiation biases in climate models and reanalyses have been associated with the poor representation of clouds, precipitation, aerosols, the atmospheric boundary layer, and their intrinsic interactions. Capitalizing on shipborne observations collected during the Clouds Aerosols Precipitation Radiation and atmospheric Composition Over the Southern Ocean 2016 and 2018 field campaigns, this research investigates and characterizes cloud and precipitation processes from synoptic to micro scales. Distinct cloud and precipitation regimes are found to correspond to the seven thermodynamic clusters established using a K‐means clustering technique, while less distinctions are evident using the cyclone and (cold) front compositing methods. Cloud radar and disdrometer data reveal that light precipitation is common over the SO with higher intensities associated with cyclonic and warm frontal regions. Multiple lines of evidence suggest the presence of diverse microphysical features in several cloud regimes, including the likely dominance of ice aggregation in deep precipitating clouds. Signatures of mixed phase, and in some cases, riming were detected in shallow convective clouds away from the frontal conditions. Two of the K‐means clusters with contrasting cloud and precipitation properties are observed over the high‐latitude SO and coastal Antarctica, suggesting distinct physical processes therein. Through a single case study, in‐situ and remote‐sensing data collected by an overflight of the Southern Ocean Clouds Radiation Aerosol Transport Experimental Study were also evaluated and complement the ship‐based analysis. Plain Language Summary: The current generation of climate models and reanalyses products have difficulties in properly representing the radiative balance over the Southern Ocean (SO), which can be traced to the poor understanding of clouds and precipitation processes in this region. The remote location of the SO is a key factor for the lack of field observations that allow the scientific community to address the above‐mentioned problem. However, recent coordinated field campaigns have collected an unprecedented amount of data, offering new opportunities to explore this understudied region. This research paper aims to study clouds and precipitation processes over the SO using shipborne data collected from two field campaigns in 2016 and 2018. Using different synoptic classification techniques, we identify unique macro and micro cloud and precipitation behaviors that correspond to the various weather patterns across a wide range of latitudes. In addition, we use aircraft observations collected from an overflight to evaluate and complement our analysis of the shipborne data. The study offers a framework that may help better understand the nature of the model biases over the SO. Key Points: Distinct cloud and precipitation regimes correspond to the Southern Ocean synoptics, defined using a sounding K‐means clustering techniqueEvidence suggests diverse microphysical features, like mixed phase in shallow convection and ice aggregation in deep precipitating cloudsTwo unique synoptic patterns have unique cloud and precipitation properties over the high‐latitudes, where climate models have large biases [ABSTRACT FROM AUTHOR]

In response to the comment on our paper "High‐resolution, multilayer modeling of Singapore's urban climate incorporating local climate zones," we provide detailed response to each of the incorrect accusations with scientifically based evidence. We have evaluated our model using all the available observational data, and the results showed good agreement. Our modeling study includes assumptions, as all modeling work does, and we have discussed their rationales and possible implications. Key Points: The published work is a state of the art scientific studyThe commenter's accusations are addressed with facts and scientific evidenceModel limitations acknowledged in the published work are reiterated [ABSTRACT FROM AUTHOR]

This paper analyzes the ensemble of regional climate model (RCM) projections for Europe completed within the EURO‐CORDEX project. Projections are available for the two greenhouse gas concentration scenarios RCP2.6 (22 members) and RCP8.5 (55 members) at 0.11° resolution from 11 RCMs driven by eight global climate models (GCMs). The RCM ensemble results are compared with the driving CMIP5 global models but also with a subset of available last generation CMIP6 projections. Maximum warming is projected by all ensembles in Northern Europe in winter, along with a maximum precipitation increase there; in summer, maximum warming occurs in the Mediterranean and Southern European regions associated with a maximum precipitation decrease. The CMIP6 ensemble shows the largest signals, both for temperature and precipitation, along with the largest inter‐model spread. There is a high model consensus across the ensembles on an increase of extreme precipitation and drought frequency in the Mediterranean region. Extreme temperature indices show an increase of heat extremes and a decrease of cold extremes, with CMIP6 showing the highest values and EURO‐CORDEX the finest spatial details. This data set of unprecedented size and quality will provide the basis for impact assessment and climate service activities for the European region. Key Points: This paper presents the first of this size regional climate model ensemble to investigate and understand the climate change response over the whole of EuropeThe paper confirms previous findings for mean and extreme climate change but is able to show the added value information of the high‐resolution regional ensembleThe paper assesses the regional and global model consensus in the projection and presents also the uncertainty of the signal [ABSTRACT FROM AUTHOR]

This paper focuses on the interdecadal variation in drought in Northeast China (NEC) in recent decades. Two dry and wet periods have occurred in the past 61 years (1950–2010). The mechanism underlying the interdecadal variation in drought in NEC is further analyzed; the results indicate that the direct cause is the interdecadal change of the Okhotsk High (OH). A strong (weak) OH is conducive (detrimental) to the convergence of cold air transported by northeast cold vortex and water vapor from the east of NEC, eventually leading to an increase (decrease) in precipitation. Furthermore, we seek to understand why OH displays such an interdecadal variation. The interdecadal increases and decreases in sea ice in the Barents Sea and the Kara Sea explain most of the interdecadal change of the OH. When more sea ice is present in this area, more energy is transferred eastward from the sea ice area to Northeast Asia, weakening the OH; in contrast, less sea ice strengthens the OH. Sensitivity simulations by Community Atmosphere Model, version 4 (CAM4) using sea ice forcing in the Barents Sea and the Kara Sea yield similar results to the observed data, further confirming our conclusion. The results of this paper provide a new understanding of the interdecadal variation in drought in NEC, and it may help to improve our ability to predict drought and provide early warning in the future. Key Points: The drought over Northeast China has significant interdecadal variability during the past decadesThe Okhotsk High acts as the direct factor causing interdecadal changes in NEC drought by affecting atmospheric circulationThe interdecadal increases and decreases in sea ice in the Barents Sea and the Kara Sea can modulate the Okhotsk High changes [ABSTRACT FROM AUTHOR]

This paper evaluates the performance of footprint models through a line source (LS) system releasing methane (CH4) measured by an eddy covariance (EC) system in a rice‐wheat rotation agro‐ecosystem. Two footprint models namely Kormann and Meixner (KM) and Flux Footprint Prediction (FFP), are used. The "line source width (LW)" was introduced, which could highly impact the model estimation, leading to an error of ∼500% for the FFP and ∼200% for the KM. The surface roughness length (z0) also affects the FFP estimation, which is much weaker than the effect of LW with a 15% error. An overestimation of 217.8% is observed when the LS is close to the EC system, which reduces to 12.2% when the source stays distant. The analysis of different experimental configurations illustrated that the estimated emission calculated based on footprint model improves with increasing emission height, averaging period, and emission rate. The most accurate estimations are achieved by the configurations of canopy level (CL; 5.5% overestimation), 15 min averaging period (1% underestimation), and moderate emission (ME; 1.9% underestimation), respectively. For KM, the CL‐ME‐30 min setup leads to the best performance, while SL (soil level)‐ME‐15 min is the best configuration for the FFP estimation. A multivariate regression model is proposed to provide preliminary guidance for the footprint model application. The designed LS system is valuable for validating the performance of flux measurements in the specific ecosystems (e.g., grassland, sand land, and forest) as well as other greenhouse gases (e.g., N2O and NH3). Plain Language Summary: A line‐source system, which can automatically simulate methane emission in the paddy fields, was designed to evaluate the performance of eddy covariance footprint models. Different emission heights, emission rates, and source distances were conducted. The result suggested that the outputs of the footprint model improved with increasing emission height and emission rate. The most accurate model estimation was found at the canopy height and the moderate emission. Finally, the range of estimation errors was calculated quantitatively, and a multivariate regression model was proposed to evaluate footprint model performance. The designed line‐source system is also available for validation in other ecosystems, such as grassland and sand land. Key Points: Footprint model estimation improves with increasing source emission height, averaging period, and emission rateSource width and emission distance can significantly affect the model performanceThe most accurate estimations are achieved at the canopy level, 15 min averaging period, and moderate emission [ABSTRACT FROM AUTHOR]

The interference of electromagnetic signals from lightning discharges in the frequency range below 100 Hz is the source of a global electromagnetic phenomenon in the Earth's atmosphere known as the Schumann resonance (SR). Changes in the parameters of SR signals caused by geophysical disturbances make it possible to study the state and dynamics of the lower ionosphere. When calculating the SR parameters, there are problems associated with the impact of electromagnetic interference of natural and anthropogenic origin. The main natural sources of interference are signals associated with the radiation of nearby lightning discharges, as well as the influence of the Alfvén ionospheric resonator. The paper presents a new method for calculating the SR parameters, which makes it possible to find the spectra distorted by interference, mention above, and exclude them from further processing. The developed technique significantly increased the temporal resolution of the obtained data on the frequency and amplitude of the SR. Due to this, it became possible to study the influence of fast heliogeophysical disturbances (such as solar X‐ray flares) on the lower ionosphere and, as a consequence, on the parameters of the SR. An analysis of the experimental data made it possible to establish a linear dependence of the SR frequency on the logarithm of the X‐ray flux in the range up to 0.2 nm during a class X solar flare. Key Points: A new method for calculating the parameters of Schumann resonance (SR) significantly reduces the impact of electromagnetic interferenceThe developed technique increased the temporal resolution of the SR frequency and amplitude dataThe new technique made it possible to establish the dependence of the SR frequency on the X‐ray flux with a wavelength of less than 0.2 nm [ABSTRACT FROM AUTHOR]

The joint influence of the stratospheric quasi‐biennial oscillation (QBO) and the El Niño Southern Oscillation (ENSO) on the polar vortex, subtropical westerly jets (STJs), and wave patterns during boreal winter is investigated in 40 years (1979–2018) of monthly mean ERA‐Interim reanalyses. The method of Wallace et al. (1993), https://doi.org/10.1175/15200469(1993)050<1751:ROTESQ>2.0.CO;2 is used to conduct a QBO phase angle sweep. QBO westerly (W) and easterly (E) composites are then segregated by the phase of ENSO. Two pathways are described by which the QBO mean meridional circulation (MMC) influences the northern winter hemisphere. The "stratospheric pathway" modulates stratospheric planetary wave absorption via the Holton‐Tan mechanism. The "tropospheric pathway" modulates the tropical and subtropical upper troposphere and lower stratosphere. QBO MMC anomalies exhibit a checkerboard pattern in temperature and arched structures in zonal wind which extend into midlatitudes, and are stronger on the winter side. During QBO W, the polar vortex and STJs are enhanced. QBO signals in the polar vortex are amplified during La Niña. During El Niño and QBO W, the strongest STJs occur, and a warm pole/wave two pattern is found. During El Niño and QBO E, a trough is found over Eurasia and a ridge over the North Atlantic, in a wave one pattern. El Niño diminishes QBO anomalies in the tropical stratosphere and reduces the poleward extent and amplitude of the QBO MMC, thereby influencing the stratospheric pathway. Effects on the boreal winter hemisphere are attributed to the combined influence of the QBO and ENSO via both pathways. Plain Language Summary: Seasonal forecasts in the Northern Hemisphere winter can be improved by a better understanding of the influence of two phenomena seated in the tropics: the stratospheric quasi‐biennial oscillation (QBO), with periodicity ∼2–3 years, and the El Niño Southern Oscillation (ENSO), with periodicity ∼3–7 years. This paper shows how the QBO and ENSO jointly influence the polar night vortex and tropospheric jet stream. During periods of QBO westerly winds, the polar vortex is stronger and more symmetric, and the tropospheric jet stream is stronger, while during QBO easterlies the vortex and jet stream are weaker. This QBO signal is enhanced during La Niña and is nearly absent during El Niño. Key Points: Two pathways are described by which the quasi‐biennial oscillation (QBO) mean meridional circulation (MMC) influences the northern winter hemisphereThe asymmetric extension of QBO MMC cells into the winter hemisphere is modulated by El Niño Southern OscillationDuring El Niño, the polar vortex anomaly exhibits a wave two pattern for QBO westerly and wave one pattern for QBO easterly [ABSTRACT FROM AUTHOR]

In this paper we coupled a crop growth model to the Weather Research and Forecasting model with its land surface model Noah‐MP and demonstrated the influence of the weather driven crop growth on land‐atmosphere (L‐A) feedback. An impact study was performed at the convection permitting scale of 3 km over Germany. While the leaf area index (LAI) in the control simulation was the same for all cropland grid cells, the inclusion of the crop growth model resulted in heterogeneous crop development with higher LAI and stronger seasonality. For the analyses of L‐A coupling, a two‐legged metric was applied based on soil moisture, latent heat flux and convective available potential energy. Weak atmospheric coupling is enhanced by the crop model, the terrestrial coupling determines the regions with the L‐A feedback. The inclusion of the crop model turns regions with no L‐A feedback on this path into regions with strong positive coupling. The number of non‐atmospherically controlled days between April and August is increased by 10–15 days in more than 50% of Germany. Our work shows that this impact results in a reduction of both cold bias and warm biases and thus improves the metrics of distributed added value of the monthly mean temperatures. The study confirms that the simulation of the weather driven annual phenological development of croplands for the regional climate simulations in mid‐latitudes is crucial due to the L‐A feedback processes and the currently observed and expected future change in phenological phases. Key Points: Coupling a crop growth model with the Weather and Research Forecasting model significantly improves the simulation of the leaf area indexLand‐atmosphere coupling strength is enhanced by weather dependent crop growth simulationThe distributed added value metric shows a reduction in temperature biases of up to 80% in croplands throughout the season in Germany [ABSTRACT FROM AUTHOR]

Water vapor in the middle atmosphere plays an essential role in global warming, ozone depletion, and the formation of polar stratospheric and mesospheric clouds. We show that tropical middle atmospheric water vapor simulated with the specified‐dynamics version of the Whole Atmosphere Community Climate Model (SD‐WACCM) is consistent with changes observed in a merged satellite data set, which encompasses the period 1993–2020. Consistent with previous work, we find no significant trend in the stratosphere in either the observations or the simulation; in the mesosphere, we find a long‐term trend of 0.1 ppmv per decade, but only in the observations. We also analyze an SD‐WACCM simulation for the longer period 1980–2019 to quantify the contribution of various factors to the decadal variation of middle atmospheric water vapor. Over 1980–1995, the simulated water vapor in the upper stratosphere and mesosphere, averaged zonally and over ±30° latitude, increases by 0.30 ppmv per decade due to increasing methane emissions. After 1995, a significant abrupt decrease of water vapor of 0.37 ppmv per decade and then a gradual increase of 0.33 ppmv per decade result from changes in stratospheric cold point temperature. The cold‐point temperature is strongly influenced by the strength of the Brewer‐Dobson circulation. The acceleration of the Brewer‐Dobson circulation before about 2003 leads to a cooler tropical tropopause and a decrease of water vapor, and the deceleration thereafter leads to corresponding warming of the tropopause and an increase in water vapor. Plain Language Summary: Water vapor in the middle atmosphere is important to global warming and ozone depletion. We analyze both satellite data and climate model output to understand its variation in the past four decades. We conclude that there is a slight increasing trend in observed mesospheric water vapor, but no significant trend in stratospheric water vapor. Model simulation results indicate that methane oxidation explains most of the increase of water vapor in the upper stratosphere and mesosphere over 1980–1995. Changes in the meridional circulation of the middle atmosphere lead to changes in the tropical tropopause temperature, which is the main factor that influences middle atmospheric water vapor over 1995–2020. Key Points: Our paper focuses on the long‐term trend and decadal variation of water vapor in the tropical middle atmosphereMethane oxidation explains most of the water vapor increases in the upper stratosphere and mesosphere over 1980–1995Changes in residual circulation lead to changes in the tropical tropopause temperature, and middle atmospheric water vapor over 1995–2020 [ABSTRACT FROM AUTHOR]

Ocean surface waves play a significant role in regulating the sea surface temperature and mixed layer depth, which are essential for accurate prediction of tropical cyclone (TC) intensity. The effects of wave breaking and wave orbital motion induced mixing on the TC intensity and size are investigated using a coupled ocean‐atmosphere‐wave model for both idealized and real TC cases. The results show that both wave breaking and wave orbital motion lead to greater sea surface temperature cooling and mixed layer deepening, resulting in decreases in TC intensity and size owing to the reduction of air‐sea heat fluxes. Wave orbital motion has a slightly greater effect than wave breaking on the TC intensity and size when the mixed layer is shallow, whereas it has a much greater effect when the mixed layer is deep. In addition, including wave orbital motion induced mixing in models can effectively reduce the error in simulated TC size. Plain Language Summary: Tropical cyclones (TCs) are powerful phenomena with tremendous destructive potential. However, some problems and limitations remain in the prediction of TC intensity and size. The TC system is very sensitive to sea surface temperature (SST), therefore accurate representation of SST is essential for TC forecasting. Surface waves have been found to play a significant role in regulating the SST and mixed layer depth. In this paper, the effects of wave breaking and wave orbital motion induced mixing on TCs are investigated using a coupled ocean‐atmosphere‐wave model. The results show that both wave breaking and wave orbital motion reduce TC intensity and size by reducing the air‐sea heat fluxes, and wave orbital motion has the greater impact. Furthermore, activating wave orbital motion induced mixing in a model improves the accuracy of the simulation of TC size. Key Points: Effects of wave induced mixing on tropical cyclones are investigated using a coupled ocean‐atmosphere‐wave modelBoth wave breaking and wave orbital motion have a negative effect on tropical cyclone intensity and sizeWave orbital motion plays a greater role in modulating the tropical cyclone system than wave breaking [ABSTRACT FROM AUTHOR]

Predicting the peak‐season (July–September) tropical cyclones (TCs) in Southeast Asia (SEA) several months ahead remains challenging, related to limited understanding and prediction of the dynamics affecting the variability of SEA TC activity. Here, we introduce a new statistical approach to sequentially identify mutually independent predictors for the occurrence frequency of peak‐season TCs in the South China Sea (SCS) and east of the Philippines (PHL). These predictors, which are identified from the preseason (April‐June) environmental fields, can capture the interannual variability of different clusters of peak‐season TCs, through a cross‐season effect on large‐scale environment that governs TC genesis and track. The physically oriented approach provides a skillful seasonal prediction in the 41‐year period (1979–2019), with r = 0.73 and 0.54 for SCS and PHL TC frequency, respectively. The lower performance for PHL TCs is likely related to the nonstationarity of the cross‐season TC‐environment relationship. We further develop the statistical approach to a hybrid method using the predictors derived from dynamical seasonal forecasts. The hybrid prediction shows a significant skill for both SCS and PHL TCs, for lead times up to four or 5 months ahead, related to the good performance of models for the sea surface temperatures and low‐level winds in the tropics. The statistical and hybrid predictions outperform the dynamical predictions, showing the potential for operational use. Plain Language Summary: Tropical cyclones (TCs) have huge impact in Southeast Asia (SEA). Seasonal forecasts of SEA peak‐season (July–September) TCs remains challenging for both statistical and dynamical models. In this paper, we introduce a novel statistical approach to sequentially identify independent predictors tailored for the frequency of SEA peak‐season TCs. The predictors are routinely constructed from far‐field sea surface temperatures and low‐level winds in the preceding‐season. The main concept in this approach is that each predictor represents a unique cluster of TC formation and propagation in the peak‐season. We also develop the approach to a hybrid prediction method by building the predictors from dynamical seasonal forecasts. The seasonal predictions based on the new approach perform much better than the current statistical and dynamical models. Such predictions can provide useful warning service for SEA TC activity 4–5 months ahead. Key Points: A new approach to identify independent predictors of Southeast Asia (SEA) tropical cyclone (TC) frequency is introducedThe preceding‐season predictors represent different clusters of TC formation and propagation through a cross‐season effectThe new method outperforms existing statistical and dynamical predictions for SEA TCs [ABSTRACT FROM AUTHOR]

The spatial and angular emission patterns of artificial and natural light emitted, scattered, and reflected from the Earth at night are far more complex than those for scattered and reflected solar radiation during daytime. In this commentary, we use examples to show that there is additional information contained in the angular distribution of emitted light. We argue that this information could be used to improve existing remote sensing retrievals based on night lights, and in some cases could make entirely new remote sensing analyses possible. This work will be challenging, so we hope this article will encourage researchers and funding agencies to pursue further study of how multi‐angle views can be analyzed or acquired. Plain Language Summary: When satellites take images of Earth, they usually do so from directly above (or as close to it as is reasonably possible). In this comment, we show that for studies that use imagery of Earth at night, it may be beneficial to take several images of the same area at different angles within a short period of time. For example, different types of lights shine in different directions (street lights usually shine down, while video advertisements shine sideways), and tall buildings can block the view of a street from some viewing angles. Additionally, since views from different directions pass through different amounts of air, imagery at multiple angles could be used to obtain information about Earth's atmosphere, and measure artificial and natural night sky brightness. The main point of the paper is to encourage researchers, funding agencies, and space agencies to think about what new possibilities could be achieved in the future with views of night lights at different angles. Key Points: Remote sensing using the visible band at night is more complex than during the daytime, especially due to the variety of artificial lightsViews of night lights intentionally taken from multiple angles provide several advantages over near‐nadir or circumstantial view geometriesNight lights remote sensing would benefit from greater consideration of the role viewing geometry plays in the observed radiance [ABSTRACT FROM AUTHOR]

The planetary boundary layer is crucial for the turbulence mixing and exchange of heat flux, momentum, and atmospheric pollutants between the atmosphere and Earth's surface. Nevertheless, the estimated boundary layer height (BLH) varies greatly by data sources and algorithms. This paper seeks to characterize the convective BLHs from 1‐s radiosonde measurements of China Radiosonde Network (CRN) for the 2012–2020 period at 1400 Beijing time, by using eight well‐known algorithms, wherein the newly established Thorpe method is theoretically fundamental on turbulence analysis and is in remarkable agreement with the parcel and bulk Richardson number methods. BLHs obtained by eight methods, ranging from 1.2 to 2.5 km, strongly vary with methods based on different kinetic or thermodynamic theories. The significant offsets among methods motivate the present study to propose a merged algorithm, to minimize the spread of BLH estimate. The merged BLH contains more physical information than that retrieved from a single method and can significantly lower the uncertainty. The BLH climatology exhibits a spatial pattern of "Southwest‐High Southeast‐Low," ascending from 0.6 km over southeastern China to 2.3 km over southwestern China, which could be largely attributed to the variations in the integrated surface sensible heat flux, soil moisture, total cloud cover, land cover, synoptic forcing, and terrain‐induced flow. Of interest is that land surface properties could be the major driver for the development of CBL. Also noteworthy is that the smallest BLH is expected under the strongest synoptic forcing condition. Plain Language Summary: The planetary boundary layer (PBL), where the exchanges of heat, moisture, momentum, and mass mainly occur with a variety of physical and chemical processes involved, is the lowest part of the troposphere in direct contact with the ground surface. However, the determination of boundary layer height (BLH) tends to be dramatically influenced by the dataset and methods used. Few studies have been conducted to evaluate the discrepancy of nationwide daytime BLH over China originating from the methods used. In particular, eight well‐known methods, including the novel Thorpe method and seven other traditional methods, are applied to estimate BLHs from high‐resolution soundings from the China Radiosonde Network. However, BLH derived by eight methods vary from approximately 1.2 to 2.5 km, strongly depending on the method. Therefore, to compile a more convincing BLH dataset eight methods are selected and composed as a merged BLH. The climatology of the merged BLH for the period 2012–2020 shows a well‐defined "Southwest‐High Southeast‐Low " pattern, which could be attributed to the diversities in sensible heat flux, soil moisture, land cover, total cloud cover, synoptic forcing, and terrain‐induced flow across China. Key Points: The merged boundary layer height (BLH) is synthesized from eight methods and it carries more planetary boundary layer (PBL) information and can considerably lower the uncertaintiesThe "Southwest‐High Southeast‐Low" pattern of BLH could be attributed to land properties, synoptic forcing, and terrain‐induced flowUnder weak synoptic forcing condition the development of convective PBL is more susceptible to the variation of land surface properties [ABSTRACT FROM AUTHOR]

The Atmosphere‐Space Interactions Monitor was designed to monitor Terrestrial Gamma‐ray Flashes (TGFs) and Transient Luminous Events (TLEs) from space, enabling the study of how these phenomena are related. In this paper, we present observations of 17 TGFs with accompanying Elves. TGFs are short and highly energetic bursts of gamma photons associated with lightning discharges, whereas Elves are TLEs that are observed as concentric rings of ultraviolet (UV) and visible light at ionospheric altitudes, produced by the excitation of N2 molecules when an electromagnetic pulse hits the base of the ionosphere. Elves were identified when optical detections in the UV band could be clearly distinguished from other optical signals from lightning strokes. The TGFs they accompanied had short durations and were associated with particularly high peak current lightning. Lightning sferics associated with these events were detected by the global lightning network GLD360 and the World Wide Lightning Location Network, and they were, with the exception of one event, observed over ocean or coastal regions. It is likely that these events were associated with Energetic In‐cloud Pulses. We show that short duration TGFs tend to be associated with higher peak currents than long duration TGFs. Key Points: We present a sample of 17 Terrestrial Gamma‐ray Flashes (TGFs) with accompanying Elves detected by Atmosphere‐Space Interactions MonitorTGFs with Elves are short and associated with very high peak current lightningThe peak currents for these events are higher than for both lightning and TGFs in general [ABSTRACT FROM AUTHOR]