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The expression "lightning never strikes twice" is questioned in this paper because, among the randomness of lightning impacts, some spots are hit even more than twice year after year. This article introduces the recurrent lightning spots (RLS) concept, which are locations periodically impacted by cloud‐to‐ground lightning every consecutive year over a certain period. RLS are investigated in two regimes, with markedly different lightning climatology but similar orography, for 10 consecutive years: Catalonia (North East of Spain, Europe) and Barrancabermeja (North Central Colombia, South America). Results revealed 148 and 916 RLS in Catalonia and Barrancabermeja, respectively. RLS in both regions are typically found to be related to tall structures, mountain peaks, and steep terrain. The method allowed us to identify those tall towers and orographic relief frequently affected by lightning that are not detected with the mere computation of the ground flash density. In the case of Catalonia, some RLS are found offshore. Besides the scientific interest in understanding lightning, the new concept of RLS provides additional and valuable information applicable to lightning protection engineering. Plain Language Summary: The expression "lightning never strikes twice" is questioned in this paper because it shows that some spots are hit even more than twice: year after year. The RLSs (RLS) concept is presented, which are locations where lightning strike them periodically. The two regions of study with markedly different lightning climatology but similar orography are Catalonia (North East of Spain, Europe) and Barrancabermeja (in North Central Colombia, South America). RLS in both regions are typically found to be related to tall structures, mountain peaks and steep terrain. In the case of Catalonia, some RLS are found offshore. RLS new concept provides valuable information to lightning protection engineering. Key Points: Recurrent lightning spots (RLS) are targets with at least one cloud‐to‐ground lightning per year during a certain number of consecutive yearsIn Catalonia (Spain), 13% of the RLS are tall towers, 72% are mountainous peaks and 5% are offshore sitesThe method effectively finds tall structures affected by lightning in tropical climates [ABSTRACT FROM AUTHOR]

Seasonal forecasts are commonly issued in the form of anomalies, which are departures from the average over a specified multiyear reference period (climatology). The model climatology is estimated as the average of the retrospective forecasts over the hindcast period. However, different operational centers that provide seasonal ensemble predictions use different hindcast periods based on their model climatology. Additionally, the hindcast periods of recently developed and upgraded newer models have shifted in the recent years. In this paper, we discuss the recent challenges faced by APCC multi‐model ensemble (MME) operations, especially changes in the hindcast period for individual models. Based on the results of various experiments for MME prediction, we propose changing the hindcast period, which is the most appropriate solution for APCC operation. This makes the newly developed models join the MME and increases the total number of participating models, which facilitates the skill improvement of the MME prediction. Plain Language Summary: In seasonal forecasting, it is well known that the MME, which combines different single‐model predictions from various operational and research centers, is a more effective way to improve forecast skill. Since 2005, the APCC has provided the MME seasonal forecasts, and the models participating in the APCC MME operations have been continuously changing. In particular, as the hindcast periods of newly developed models shift to the latest, they cannot participate in operational MME forecasts because of climatological discrepancies. However, over time, as the number of new models expected to provide skillful forecasts gradually increases, the APCC faces the challenge of continuously reducing the number of participating models or changing the hindcast period to more recent years. Considering various aspects such as the number of participating models, skills, and climatology period, we selected the most appropriate method for APCC operation. Thus, the MME prediction skill has improved over most of the globe and seasons because of the increase in the number of participating models, particularly the inclusion of newer models. Key Points: APCC, which combines all the information from different ensemble prediction systems, recently faced challenges in hindcast period issuesThe proposed solution leads to an increase in the number of models contributing to MME prediction, particularly recently developed modelsIt shows improved skills for both temperature and precipitation predictions over most of the globe and seasons [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]

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]

This study establishes a new blocking climatology in the Southern Hemisphere (SH) by using the improved detection method with the reanalysis data from 1979 to 2016. Furthermore, it investigates the dynamical linkage between SH blocking and ENSO phases. It is found that the ENSO warm phase is more conducive to the blocking formation than the cold phase while the blocking intensity is not affected by the ENSO phases. In addition, blocking in ENSO warm phase is characterized with upper‐level divergence anomaly and the cold phase with convergence anomaly equatorward of blocking onset region. Through the diagnostic analysis of tropopause divergence for the composite blocking events via an improved divergence tendency equation, the study shows that the ageostrophic effect exhibits dual effects, namely, it induces anticyclonic ageostrophic vorticity favoring the formation of blocking whereas it results in convergence anomaly close to the blocking onset region thus inhibiting blocking locally. In addition, the nonlinear term in the divergence tendency equation is found to be a dominant forcing for favoring blocking onset. Nevertheless, despite the primary contributions from the ageostrophic effect and nonlinear term to blocking formation, they could barely explain the SH blocking onset preference in ENSO warm phase. Finally, through the localized Eliassen‐Palm flux this study reveals that in ENSO warm phase the composite blocking onset region and the immediate upstream region are characterized by more localized EP flux convergence, thereby leading to more effective westerly wind weakening and favoring the blocking formation. Plain Language Summary: Previous research shows that in the Southern Hemisphere (SH), the ENSO warm phase is more conducive to the blocking formation than the cold phase, but the dynamic reasons are rarely studied. Starting from the tropopause divergence with the improved divergence tendency equation and tropical Rossby wave propagation associated with midlatitude wave‐flow interaction, this paper studies the connection between the tropics and extratropics from these two perspectives. Finally, this study reveals that the ENSO warm phase is more conducive to the blocking formation than the cold phase in the SH. Key Points: New blocking climatology is established in the Southern Hemisphere (SH) using an improved detection methodThe ageostrophic wind plays a dual effect in the SH blocking formationENSO warm phase is more conducive to blocking formation in the SH with more eddy convergence [ABSTRACT FROM AUTHOR]

This paper makes use of spaceborne observational data sets in order to characterize radiative processes involved in spring time heat waves in the Sahel. Spring corresponds to the hottest period of the year, with a high aerosol load, a gradual moistening, and the presence of clouds contributing to greenhouse effect. Heat waves are defined as synoptic events that have a large spatial extent and a duration longer than 3 days. Two types of heat waves are studied: daytime heat waves, detected with the daily maximum temperature and nighttime heat waves, detected with the daily minimum temperature. Daytime heat waves correspond to situations where cloud optical thickness is lower than the climatology and a large number of these situations are also associated with a lower aerosol load and a drier atmosphere. Nighttime heat waves correspond to a moister atmosphere compared to the climatology. In a large fraction of them, an increase in aerosol loading is also observed. This study, only based on observational data sets, highlights the subtle but different radiative balance at play in both types of events. Key Points: Observational data sets are used to statistically document processes involved in spring time heat waves in the SahelNighttime heat waves are linked to an increase in precipitable water as well as a frequent high aerosol loadDaytime heat waves are generally associated with cleaner skies; more intense events show in addition a higher amount of precipitable water [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) are long and narrow filaments of vapor transport that are responsible for most poleward moisture transport outside of the tropics. Many AR detection algorithms have been developed to automatically identify ARs in climate data. The diversity of these algorithms has introduced appreciable uncertainties in quantitative measures of AR properties and thereby impedes the construction of a unified and internally consistent climatology of ARs. This paper compares nine global AR detection algorithms from the perspective of AR lifecycles following the propagation of ARs from origin to termination in the MERRA2 reanalysis over the period 1980–2017. Uncertainties in AR lifecycle characteristics, including event number, lifetime, intensity, and frequency distribution are discussed. Notably, the number of AR events per year in the Northern Hemisphere can vary by a factor of 5 with different algorithms. Although all algorithms show that the maximum AR origin (termination) frequency is located over the western (eastern) portion of ocean basins, significant disagreements appear in regional distribution. Spreads are large in AR lifetime and intensity. The number of landfalling AR events produced by the algorithms can vary from 16 to 80 events per year, although the agreement improves for stronger ARs. By examining the ARs' connections with the Madden‐Julian Oscillation and El Niño Southern Oscillation, we find that the overall responses of ARs (such as changes in AR frequency, origin, and landfall activity) to climate variability are consistent among algorithms. Plain Language Summary: Atmospheric rivers (ARs) are one of the major mechanisms by which water vapor is transported from the tropics to high latitudes and, therefore, dictate water resource availability in many coastal regions such as the west coast of North America. As such, many studies have developed detection algorithms to isolate and study the characteristics of ARs. However, conclusions from these studies may differ because of algorithm design assumptions. Here we select nine detection algorithms that have been applied to a common data set which describes the meteorological conditions of the recent past. This analysis framework enables us to identify the disagreements in AR characteristics across algorithms including AR size, event number, lifetime, intensity, and landfall activity. Results suggest that basic AR characteristics vary significantly depending on the detection algorithm. However, algorithm differences may be ameliorated when AR behavior is analyzed over intraseasonal and interannual time scales. Key Points: Detection algorithms introduce uncertainties in the number, lifetime, and intensity of atmospheric rivers (AR) lifecyclesAgreement in landfall activity across detection algorithms increases with stronger ARsUncertainties may be smoothed out when investigating AR activity at intraseasonal and interannual time scales [ABSTRACT FROM AUTHOR]

This study assesses the benefit of convective‐scale data assimilation (DA) for model initialization using well‐known functional relationships between lightning flash rate and vertical velocity. Based on the relationships, a lightning DA scheme to update model kinematic states was implemented in the Weather Research and Forecasting Data Assimilation (WRFDA) three‐dimensional variational (3DVar) system. This scheme combines total lightning observations with model‐based prescribed vertical velocity profiles to retrieve kinematic information through a DA scheme. With the availability of space‐borne lightning imagers in recent years, total lightning observations from the Lightning Mapping Imager (LMI) on board the FY‐4A geostationary satellite were assimilated in combination with radar DA. A detailed analysis of the impact of the lightning DA scheme on convective precipitation forecasting was conducted using a squall line case over Beijing on 13 July 2017. The assimilation of LMI data provides added benefits to the assimilation of radar radial winds by reducing wind errors and strengthening convergence along the squall line in the analysis. Although the microphysical states are identical due to the assimilation of reflectivity, the lightning DA scheme helps in promoting updraft developments at lightning observation locations, which improves the representation of mixed‐phase convection. The quantitative verification of short‐term convective forecasts indicated that the lightning DA adds value to the radar DA by improving the precipitation forecast skill. The lightning DA scheme was evaluated further for a heavy rainfall case in 2018 over the Beijing metropolitan area and revealed overall similar forecast improvements for composite reflectivity and accumulated rainfall. Plain Language Summary: Lightning flashes are closely related to the upward air motions in thunderstorms and hence are indicative of strong wind convergence. Currently, lightning imagers on board the geostationary satellites provide increased availability of lightning data over broad regions and can improve weather forecasting accuracy. This paper describes how the space‐borne lightning observations could be employed to update model kinematic states and improve convective precipitation forecasting. Key Points: A lightning data assimilation (DA) scheme to update model kinematic states was developed using a three‐dimensional variational (3DVar) systemThe event data from Lightning Mapping Imager (LMI) aboard the FY‐4A geostationary satellite were assimilated to reflect lightning horizontal dimensionThe new lightning DA scheme improves the convective analysis and storm forecasting in two severe convective cases [ABSTRACT FROM AUTHOR]

It is challenging to develop observationally based spatial estimates of meteorology in Alaska and the Yukon. Complex topography, frozen precipitation undercatch, and extremely sparse in situ observations all limit our capability to produce accurate spatial estimates of meteorological conditions. In this Arctic environment, it is necessary to develop probabilistic estimates of precipitation and temperature that explicitly incorporate spatiotemporally varying uncertainty and bias corrections. In this paper we exploit the recently developed ensemble Climatologically Aided Interpolation (eCAI) system to produce daily historical estimates of precipitation and temperature across Alaska and the Yukon Territory at a 2 km grid spacing for the time period 1980–2013. We extend the previous eCAI method to address precipitation gauge undercatch and wetting loss, which is of high importance for this high‐latitude region where much of the precipitation falls as snow. Leave‐one‐out cross‐validation shows our ensemble has little bias in daily precipitation and mean temperature at the station locations, with an overestimate in the daily standard deviation of precipitation. The ensemble is statistically reliable compared to climatology and can discriminate precipitation events across different precipitation thresholds. Long‐term mean loss adjusted precipitation is up to 36% greater than the unadjusted estimate in windy areas that receive a large fraction of frozen precipitation, primarily due to wind induced undercatch. Comparing the ensemble mean climatology of precipitation and temperature to PRISM and Daymet v3 shows large interproduct differences, particularly in precipitation across the complex terrain of southeast and northern Alaska. Plain Language Summary: It is challenging to create spatial maps of precipitation and temperature in Alaska and the Yukon. The rugged terrain and extreme conditions, particularly snow and wind, along with the extremely sparse station networks, limit our ability to estimate historical conditions. Thus, it is critical to understand the uncertainty in our spatial estimates of meteorological conditions. Here we develop a new estimate of uncertainty for historical meteorology and include corrections to precipitation measurements for errors due to snowfall and wind. We show that there are large differences between several independent mapping efforts. We then demonstrate that our ensemble product skillfully predicts the observed probability of occurrence of multiple precipitation events sizes (the ensemble is statistically reliable). Finally, our precipitation corrections increase precipitation estimates by more than 30% in some portions of Alaska. Key Points: It is difficult to estimate the spatial variability in meteorology across the Arctic due to complex topography, sparse observations, and frozen precipitationWe developed a probabilistic approach to estimate precipitation and temperature, including precipitation undercatchThere are large uncertainties in our precipitation and temperature estimates over much of Alaska [ABSTRACT FROM AUTHOR]

Quantifying the underground water exchange between adjacent regions is a common question in field investigations and groundwater flow models. This paper proposes an innovative approach to assess underground water exchange patterns based on Gravity Recovery and Climate Experiment (GRACE) observations, the water balance method, and Darcy's law. The dynamic patterns of flux changes are investigated over four boundaries of an arid plain. Moreover, the causes of anthropogenic and climate factors are evaluated using the entropy method and the partial least squares regression (PLSR) model. The results indicate that terrestrial water storage (TWS) in the study area shows a decreasing trend at a rate of −1.77 ± 0.21 mm/yr from 2003 to 2015. The water resources recharging the study area from its southern boundary show a noticeable increasing trend, which is mainly attributed to the warming climate and increasing precipitation on the Qilian Mountains. The Ecological Water Diversion Project and the imbalance between precipitation and evapotranspiration are the main factors inducing the decline of flux changes for the northern, western, and eastern boundaries. Under the constrains of empirical values of hydrogeological parameters, GRACE‐based methods find that increment of the flux changes in the southern boundary may account for approximately 0.43% of the investigated flux in 2000, and the decrement of flux changes in the eastern boundary may be about 0.01% to the previous measured results. Anthropogenic activities are the dominant driving force for the changes in water resources, with the weight of 88.70%. The presented method can provide insights into the patterns of flux change in data‐poor areas. Key Points: An innovative approach is proposed to assess underground water exchange between regions using GRACE dataWater resources recharged from the southern boundary show a noticeable uptrend owing to the warming climate and increasing rainfallThe influences of anthropogenic and climate factors are evaluated using the entropy method and the PLSR mode [ABSTRACT FROM AUTHOR]

Microbursts are meteorological phenomena in the lower troposphere which can produce damaging surface winds and pose a severe risk to aircraft flying close to the ground. As these events usually span less than 4 km and 15 min, the spatiotemporal resolution is a challenge for numerical simulations. Although research of microburst using operative mesoscale models is scarce, the Weather Research and Forecasting (WRF) model has been used in the diagnosis of this phenomenon. In this paper, such model is used to simulate several microburst conducive days using two different boundary conditions. The energy spectra of the simulations are computed to evaluate the effective resolution of the model. The results are in line with previous studies and produce no notable differences among the boundary conditions. Nonetheless, the energy spectra show an overenergetic troposphere at microscale resolutions, rendering the effective resolution inadequate for microburst forecasting using the simulated physics variables. Thus, mesoscale indices are analyzed as a prognostic tool. The wind index, the wet microburst severity index and the microburst windspeed potential index do not show high forecasting performances, even though improving the results of climatology. Also, notable differences among the boundary conditions can be seen. The most consistent results are achieved by the wet microburst severity index. Key Points: The WRF model shows an unrealistic energy spectrum when microscale spatial resolutions are usedThe effective resolution of the simulations casts doubts over the ability to forecast microburstsWINDEX, WMSI, and MWPI microburst indices show better forecasting performance than climatology, despite being suboptimal in general terms [ABSTRACT FROM AUTHOR]

The Atlantic multidecadal variability (AMV) acts as a key source of multidecadal variability and plays an important role in climate change in many regions of the Northern Hemisphere, resulting in great social and economic impacts. This paper shows that, since the late 19th century, the AMV has experienced a significant increasing trend. The AMV intensified at a rate of 0.0040°C per decade from 1870 to 2014, which is statistically significant at the 95% confidence level. The AMV teleconnects the amplified signal from the North Atlantic across the Eurasian continent to North America through a circumglobal teleconnection pattern, which further intensifies the regional climate variability and climate extremes in North Africa, Europe, East Asia, and North America. Results from the single‐forcing and all‐but‐one‐forcing experiments of the Community Earth System Model, version 1, indicate that anthropogenic aerosol emissions have played a more important role in the AMV intensification compared to other external forcings, especially during the period from the 1900s to 1990s. Key Points: The AMV has experienced a significant increasing trendThe intensified AMV has amplified the regional climate variability and climate extremes in the Northern HemisphereAnthropogenic aerosol emissions have played an important role in the AMV intensification [ABSTRACT FROM AUTHOR]

This paper investigates the performance of 10 Regional Climate Models (RCMs) hindcasts from the Coordinated Regional Climate Downscaling Experiments (CORDEX) over Central Africa, covering the period 1998–2008 and performed over a common model grid spacing 0.44° (∼50 km). Multiple observational data sets are used to evaluate model performances over four targeted subregions. Throughout the work, a measure of observational uncertainty is made and we discuss whether or not the models are found within or outside the range of observational uncertainty. Results indicate that RCMs generally capture rainfall and temperature basic features, though important biases exist and vary for models and seasons. Dry (wet) biases are common features over the Congo basin (northern and southern part of the domain). In terms of precipitation and temperature in both seasonal and annual scale, most RCMs along with their ensemble mean generally fall in the range of observational uncertainty. Furthermore, most RCMs show a good spread of grid points where the added value of RCMs is found although the added value in temperature is not as great as with precipitation. UC‐WRF is among models adding less value on ERAINT and this could explain why whatever the time scale of variability, UC‐WRF outputs are generally out from the observational uncertainty. The multimodel ensemble mean is generally found within observational range when most models are there as well. This highlights the fact that the ensemble mean, built from the equal treatment of RCMs, does not generally outperform individual RCMs realization as it is reported in several previous studies. Key Points: Most RCMs along with their ensemble mean generally fall in the range of observational uncertaintyThe ensemble mean of models is generally found within the observational range when most models are there as wellThe ensemble mean of models does not generally outperform individual RCMs realization as it is reported in several previous studies [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) are now widely known for their association with high‐impact weather events and long‐term water supply in many regions. Researchers within the scientific community have developed numerous methods to identify and track of ARs—a necessary step for analyses on gridded data sets, and objective attribution of impacts to ARs. These different methods have been developed to answer specific research questions and hence use different criteria (e.g., geometry, threshold values of key variables, and time dependence). Furthermore, these methods are often employed using different reanalysis data sets, time periods, and regions of interest. The goal of the Atmospheric River Tracking Method Intercomparison Project (ARTMIP) is to understand and quantify uncertainties in AR science that arise due to differences in these methods. This paper presents results for key AR‐related metrics based on 20+ different AR identification and tracking methods applied to Modern‐Era Retrospective Analysis for Research and Applications Version 2 reanalysis data from January 1980 through June 2017. We show that AR frequency, duration, and seasonality exhibit a wide range of results, while the meridional distribution of these metrics along selected coastal (but not interior) transects are quite similar across methods. Furthermore, methods are grouped into criteria‐based clusters, within which the range of results is reduced. AR case studies and an evaluation of individual method deviation from an all‐method mean highlight advantages/disadvantages of certain approaches. For example, methods with less (more) restrictive criteria identify more (less) ARs and AR‐related impacts. Finally, this paper concludes with a discussion and recommendations for those conducting AR‐related research to consider. Key Points: The large number of atmospheric river identification/tracking methods produces large uncertainty related to AR climatology and impactsUncertainty is quantified using the same data (MERRA v2), time period (1980–2017), region (global where possible), and common metricsThis study presents recommendations regarding the advantages/disadvantages of certain approaches based on science application [ABSTRACT FROM AUTHOR]

Stochastic schemes, designed to represent unresolved subgrid‐scale variability, are frequently used in short and medium‐range weather forecasts, where they are found to improve several aspects of the model. In recent years, the impact of stochastic physics has also been found to be beneficial for the model's long‐term climate. In this paper, we demonstrate for the first time that the inclusion of a stochastic physics scheme can notably affect a model's projection of global warming, as well as its historical climatological global temperature. Specifically, we find that when including the "stochastically perturbed parametrization tendencies" (SPPT) scheme in the fully coupled climate model EC‐Earth v3.1, the predicted level of global warming between 1850 and 2100 is reduced by 10% under an RCP8.5 forcing scenario. We link this reduction in climate sensitivity to a change in the cloud feedbacks with SPPT. In particular, the scheme appears to reduce the positive low cloud cover feedback and increase the negative cloud optical feedback. A key role is played by a robust, rapid increase in cloud liquid water with SPPT, which we speculate is due to the scheme's nonlinear interaction with condensation. Plain Language Summary: Accurate estimates of the extent of global warming by 2100 are crucial for determining effective climate policies. However, large uncertainties still remain, due in large part to uncertainties in the response of clouds to global warming. Model uncertainties arise largely from the need to crudely estimate the effects of processes too small to represent perfectly (given the limits of current computing power). "Stochastic schemes" aim to represent such errors, thereby, potentially, improving climate models. Indeed, many such improvements have been found over the last decade. In this paper, we show that the inclusion of such a scheme in one particular climate model has the effect of reducing the projected global warming by 10%. We link this to the scheme having changed the response of clouds to global warming. A potential consequence of this result is that carefully calibrated stochastic schemes could, by representing model errors, improve the accuracy of global warming projections. Key Points: The inclusion of a stochastic scheme reduces climate sensitivity in a general circulation modelThis reduction, of around 10%, is linked to changes in cloud cover and cloud optical depth feedbacksWell‐calibrated stochastic schemes may give more accurate global warming projections [ABSTRACT FROM AUTHOR]

Active observations from profiling instruments such as cloud radar or lidar have proved invaluable in improving our understanding of clouds and their interaction with the atmosphere. However, while they undoubtedly contain a wealth of information about the atmospheric state, the assimilation of such observations into NWP models has so far had mixed success. One reason is the mismatch of scales between the relatively coarse model resolution and the narrow beam‐width of the instruments. To obtain an optimal analysis, this representativity error due to this mismatch in scales must be included within the observation error covariance matrix. In this paper, we demonstrate how a relatively straightforward approach that uses the local variance of the measurement combined with a global estimate of correlation provides a useful estimate of the representativity error. We also show how the method can be used to estimate the correlation in representativity error between observations in both the horizontal and vertical, potentially removing the need to thin the observations, or inflate their observation error. The method is evaluated using 2‐D and 3‐D fields of simulated and observed radar reflectivity before an example application to profiling observations is shown using Cloudsat data. Key Points: Cloud profiling observations can have large sampling errors relative to NWP model gridboxesSampling errors can be predicted using along‐track variability and climatological correlationCorrelations in sampling error between vertical levels can be significant [ABSTRACT FROM AUTHOR]

Vb cyclones typically emerge in the Western Mediterranean and propagate to the Northeast into Central Europe. This paper explores the temporal characteristics of Vb cyclone occurrence based on cyclone tracks identified at the atmospheric levels of Z700 and sea level pressure, using JRA‐55 reanalysis data for the period 1959–2015. The risk of Vb occurrence was significantly high in the 1960s and has remained at a lower level since then. Vb cyclones do not occur fully randomly according to a Poisson point process. Eleven well‐separated and distinct clusters as well as 11 hiatus periods are identified, with average occurrence rates of 21.5 and 5.2 yrea−1, respectively. During the event of Vb, the large‐scale atmospheric circulation is changed into a state favoring the development of successive Vb cyclones. Clustering is very prominent in the case of Genoan Vb cyclones in summer as well as those Vb cyclones developing over the Iberian Peninsula or the North African Coast in winter. Superposition of the polar and the subtropical jet stream over the Western Mediterranean is identified as a main feature at the onset of Vb cyclones. Vb cyclone occurrence appears to be synchronized with the Northern Atlantic Oscillation (NAO; at Z500) and Arctic Oscillation (AO; at Z1000). Clusters have occurred when both NAO and AO were negative. This relation applies to Western Mediterranean cyclones not following a Vb track as well, however to a much weaker extent. In contrast, Vb cyclone frequency was particularly low from 1988 to 1997 during a sustained positive phase of both NAO and AO. Key Points: In the past 50 years, the frequency of Vb cyclones was high in the 1960s and lower since thenVb cyclones were strongly synchronized with NAO and AO; high frequency clusters occurred when NAO and AO were negativeThe coupling of the polar and the subtropical jet stream over the Western Mediterranean is a driving mechanism of the onset of Vb cyclones [ABSTRACT FROM AUTHOR]

Abstract: To better understand the potential effects of climate change on atmospheric dynamics, this paper studies Rossby wave breaking and isentropic stratosphere‐troposphere exchange (STE) in the Northern Hemisphere between 320 and 380 K during 1981–2015 using the Modern‐Era Retrospective Analysis for Research and Application version 2 data. The isentropic STE is estimated using Contour Advection. Our results show that anticyclonic wave breaking events have become more frequent, especially in summer at higher isentropic surfaces, and cyclonic wave breaking events have become less frequent at 320 K. The anticyclonic wave breaking has shifted poleward in summer. The isentropic STE is found to be strongest over the regions where Rossby wave breaking activities are most frequent. Both isentropic STE and Rossby wave breaking are shown to be strongest in summer and weakest in winter. Our results do not show any discernable trends during isentropic STE during 1981–2015. [ABSTRACT FROM AUTHOR]

We introduce a new climate model (GISS E2.2) that has been specially optimized for the middle atmosphere and whose output is being contributed to the CMIP6 archive. The top of the model is at a geopotential altitude of 89 km, and parameterizations of moist convection and various forms of gravity wave drag based on tropospheric processes are chosen specifically for this optimization. We first evaluate the model in its configuration as a coupled atmosphere‐chemistry model with respect to its simulation of the mean state of the middle atmosphere, from the mesosphere down through the upper troposphere/lower stratosphere. Then we assess its use as a coupled atmosphere‐ocean climate model by exploring its mean ocean climatology. To evaluate its variability, we report on its simulation of the primary modes in the troposphere, stratosphere, and ocean. Two climate change simulations are presented, the responses to instantaneous increases of 2xCO2 and 4xCO2, run with two different ocean models. Sensitivity studies are performed to illustrate the effect of parameterizations on the model results. We compare these results to the lower vertical resolution/top GISS Model E2.1, whose output has also been submitted to CMIP6. The different choices made for these models are explored. It is shown that important improvements in the circulation above and below the tropopause can be obtained when attention is paid to representation of middle atmosphere processes in climate model development. Plain Language Summary: A new "high‐top" GISS climate model with results submitted to the CMIP6 archive is described, and the model development is explained. The model was optimized to produce a realistic middle atmosphere, which involved its simultaneous assessment along with its simulation of tropospheric climate. In particular, the interplay between the parameterization of convection in the troposphere and the dynamics of the middle atmosphere requires appreciation of the needs of both regions. Key Points: This article presents the new GISS "high‐top" climate modelIt discusses the advantages of a higher model top and increased vertical resolutionIt emphasizes the need for the middle atmosphere to be a focus in climate model development [ABSTRACT FROM AUTHOR]

The climatologies of the stratopause height and temperature in the UA‐ICON model are examined by comparing them to 17‐years (2005–2021) of Microwave Limb Sounder (MLS) observations. In addition, the elevated stratopause (ES) event occurrence, their main characteristics, and driving mechanisms in the UA‐ICON model are examined using three 30‐year time‐slice experiments. While UA‐ICON reasonably simulates the large‐scale stratopause properties similar to MLS observations, at polar latitudes in the Southern Hemisphere the stratopause is ∼8 K warmer and ∼3 km higher than observed. A time lag of about two months also exists in the occurrence of the tropical semiannual oscillation of the stratopause compared to the observations. ES events occur in ∼20% of the boreal winters, after major sudden stratospheric warmings (SSWs). Compared to the SSWs not followed by ES events (SSW‐only), the ES events are associated with the persistent tropospheric forcing and prolonged anomalies of the stratospheric jet. Our modeling results suggest that the contributions of both gravity waves (GW)s and resolved waves are important in explaining the enhanced residual circulation following ES events compared to the SSW‐only events but their contributions vary through the lifetime of ES events. We emphasize the role of the resolved wave drag in the ES formation as in the sensitivity test when the non‐orographic GW drag is absent, the anomalously enhanced resolved wave forcing in the mesosphere gives rise to the formation of the elevated stratopause at about 85 km. Plain Language Summary: Using 17 years (2005–2021) of Microwave Limb Sounder (MLS) observations, we show negative (cooling stratopause temperatures and decreasing stratopause heights) trends in most regions and seasons. The largest negative trend in the stratopause temperature (by considering all regions and all seasons) is found in the Southern Hemisphere (SH)'s polar region during austral spring. The seasonal average of cooling rates is comparable in the mid‐latitudes of Northern Hemisphere and SH. In the UA‐ICON simulations, the elevated stratopause events (ESEs) occur after major sudden stratospheric warmings (SSWs). ESEs frequency is 2 events per decade in UA‐ICON simulations. Our results show that the wind reversal is stronger and long‐lasting in the ESEs compared to SSW‐only events. In addition, the easterlies extend to the mesosphere in the composites of ESEs, but the reversed winds are limited to below 60 km in the case of SSW‐only events. We show that the non‐orographic gravity wave drag induces anomalous residual circulation after SSW that causes the ESEs. We also show that the ESEs form even in the absence of non‐orographic gravity wave drag. In this case, the anomalous residual circulation is due to the anomalously enhanced resolved wave forcing in the mesosphere that gives rise to the formation of the ESEs at about 85 km. Key Points: The largest stratopause trend is found in the Southern Hemisphere polar region during austral springbased on Microwave Limb Sounder observationsThe suppression of gravity waves in UA‐ICON reveals the importance of resolvedwaves and their ability to compensate missing dragIn the polar regions, the simulated stratopause is too warm and the tropical semi‐annual oscillation is about two months out of phase [ABSTRACT FROM AUTHOR]

Driven by ERA‐Interim reanalysis, two climate simulations are conducted from April to August for 20 years (1998–2017) during the East Asia summer monsoon with Model for Prediction Across Scale‐Atmosphere (MPAS‐A). The global variable‐resolution (MPAS‐VR) and regional (MPAS‐RCM) configurations are adopted under the same model framework with 92–25 km mesh refinement centered over Mainland China (MPAS‐A experiments hereafter). MPAS‐VR allows flexible interactions across scales. Constrained by the "reanalysis‐based" lateral boundary conditions (LBCs), MPAS‐RCM could well capture the evolution of large‐scale fields and becomes a proper reference for evaluating MPAS‐VR. The evaluations are conducted for precipitation, near‐surface air temperature, and circulation features against observed climate. Two MPAS‐A experiments present comparable results for the mean climatology and interannual variability except that MPAS‐VR presents wet biases along the tropical ocean and underestimation in the Yangtze–Huaihe River basin. Compared with MPAS‐VR, MPAS‐RCM presents better daily variations and rain belts' evolution, which demonstrates the crucial effects of the LBCs for the limited‐area model. The simulated circulation and moisture flux can explain most of the deviations. However, two MPAS‐A experiments show consistent results for the extreme precipitation frequency and the extreme indices over Mainland China. With the same dynamic core and model physics, those climate features are similarly resolved by the two simulations. Thus, the 92–25 km MPAS‐VR simulation is demonstrated as a promising tool for regional climate hindcast. Plain Language Summary: In this work, we conduct model experiments by two configurations during the East Asia summer monsoon using Model for Prediction Across Scale‐Atmosphere with refinement mesh centered over Mainland China. The global variable‐resolution configuration (MPAS‐VR hereafter) allows flexible interaction across global features to regional climate details. Constrained by the reanalysis (which blends simulated and observed results) around the boundary, the regional limited‐area configuration with the truncated mesh (MPAS‐RCM hereafter) is used for identifying the model's biases mostly related to its dynamic core and parameterization, which is a proper reference for MPAS‐VR. We evaluate the model's performances against the observed climate for the near‐surface air temperature and precipitation. Using MPAS‐RCM as the criterion, MPAS‐VR well captures the mean climatology, interannual variability, and extreme events, which demonstrates itself as a promising tool for regional climate details. The diverged circulation in the two experiments can explain most of the simulated biases. Extreme precipitation frequency and extreme indices over Mainland China suggest similar deficiencies in the two simulations due to a common model framework. Key Points: Dynamical downscaling is conducted by Model for Prediction Across Scale for Atmosphere (MPAS‐A) with a global variable‐resolution (MPAS‐VR) and truncated regional (MPAS‐RCM) configurationsTwo MPAS‐A experiments present comparable results with simulated circulation explaining most of their divergencesExtreme frequency and indices over Mainland China suggest similar deficiencies in the two simulations due to a common model framework [ABSTRACT FROM AUTHOR]

Climate models are widely used to project future climate changes and analyze underlying mechanisms. However, it remains unknown whether the earlier precipitation projections match the subsequent observations in recent decades, which is the scientific basis for the confidence of precipitation projections and associated impacts. Here, we find models in the Third (TAR), Fourth (AR4), and Fifth (AR5) Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC) skillfully project the subsequent climatological changes in global mean land precipitation for 2002–2020, 2008–2020, and 2014–2020 (relative to 1980–1999 climatology) from several to 10 years ahead, respectively. Skillful regional projections are mainly found in the northern mid to high latitudes. IPCC models are less skillful in projecting subsequent changes in land precipitation at regional scales than at global scales, which is likely to be at least partly explained by the lower signal‐to‐noise ratio. Plain Language Summary: As an important tool, climate models are widely used to project future climate changes and analyze underlying mechanisms. The precondition of this is that the projections of climate models are credible. The most convincing way of validating the credibility of climate projections is to quantify the extent to which past projections agree with subsequent observations. Here, we provide a comprehensive analysis on the skill of past climate models in projecting the subsequent precipitation changes over global land. Results show that models have robust skills in projecting the subsequent climatological changes in global mean land precipitation from several to 10 years ahead. Relative to global scale land, the models are less skillful in projecting the subsequent changes in precipitation at regional scale, although they exhibit some skills in northern mid‐ to high‐latitudes. Key Points: Models show robust skills in projecting the subsequent climatological changes in global mean land precipitation from several to 10 years aheadRelative to global scale, models are less skillful in projecting the subsequent climatological changes in precipitation at regional scaleThe near‐term precipitation projections are similar under various emission scenarios [ABSTRACT FROM AUTHOR]

Heavy rainfall is a challenge to forecast due to the variety of rainfall intensities and durations across a wide spectrum of high‐impact storm types. In this study, we analyze extreme storms in Tropical and Subtropical East Asia, a moisture‐rich environment with complex terrain and oceanic regions. The Tropical Rainfall Measuring Mission's Precipitation Radar is utilized to characterize the frequency and rainfall intensity of four extreme storm types. Extreme storms producing heavy precipitation are categorized into four types: deep convective cores (DCCs), deepwide convective cores (DWCCs), wide convective cores (WCCs), and broad stratiforms regions (BSRs). DCCs and DWCCs occur more frequently and produce stronger rain intensities over land compared to those over ocean. However, WCCs and BSRs occur more frequently over oceans, especially in association with the Meiyu front season and climatological progression in the northern subregions. Although the Convective Cores show higher rain intensities than the BSRs, they show lower volumetric rain rate due to their comparatively smaller horizontal area. An ingredients‐based framework is applied to find key similarities across the different heavy rainfall‐producing storms near Taiwan using ERA5 reanalysis. The analysis shows that the broader systems (i.e., WCCs and BSRs) are associated with larger in area and longer timescales of vertical moisture flux and low‐level wind shear that support the development of the horizontally large, organized storms. Smaller DCCs do not show strong vertical moisture flux on the spatial scales resolved by the reanalysis, suggesting their more local nature and less meso‐ or synoptic scale support. Plain Language Summary: Heavy rainfall is a challenge to forecast due to the variety of rainfall intensities and durations across a wide spectrum of high‐impact storm types. In this study, we analyze extreme storms in Tropical and Subtropical East Asia (TSEA), a moisture‐rich environment with complex terrain and oceanic regions. Observations from the first satellite precipitation radar are used to characterize the nature of extreme storms. Results show that deep convective storms occur more frequently over land, while the wide convective storms and the broad stratiform regions occur more frequently over oceans, especially in association with the Meiyu front (pre‐East Asian monsoon season) in northern TSEA. Broad stratiform regions can produce a larger total rainfall amount compared to the convective rain categories because of larger areas. A goal of this study is to identify similar key ingredients across different extreme storm types near Taiwan. Analysis shows that the broader storms are associated with moisture in larger areas and on longer timescales, and also low‐level wind shear that supports the development of the large, organized storms. Smaller deep convective storms do not show strong moisture signals in coarse‐scale environmental analysis, suggesting that this storm type might need more small‐scale moisture support. Key Points: The spatio‐temporal and rain frequency of extreme storm types in Tropical and Subtropical East Asia is documentedBroad stratiform environments, for example, in Meiyu Front, require a longer and larger moisture build‐upSmaller convective systems require spatially smaller diurnal vertical moisture flux and convergence [ABSTRACT FROM AUTHOR]

Subseasonal tropical cyclone (TC) reforecasts from the Community Earth System Model version 2 (CAM6) subseasonal prediction system are examined in this study. We evaluate the modeled TC climatology and the probabilistic forecast skill of basin‐wide TC genesis at weekly temporal resolution. Prediction skill is calculated using the Brier skill score relative to a constant annual mean climatology and to a monthly varying seasonal climatology during TC season. The model captures the observed basin‐wide climatological TC seasonality and spatial distributions at weeks 1–6, but TC genesis is largely underestimated from Week 2 onward. For some basins and lead times, the predicted TC genesis is primarily controlled by the number of TC "seeds" and the mean‐state climate condition. The model has good prediction skill relative to the constant climatology across all the basins and lead times, but is only skillful in the eastern Pacific, North Indian Ocean, and Southern Hemisphere at Week 1 when compared to the seasonal climatology, indicating limited skill in predicting deviations from the seasonal cycle. We find strong modulations of the predicted TC genesis at up to 3 weeks of forecast lead time by the Madden‐Julian Oscillation. The interannual variability of predicted TC genesis and accumulated cyclone energy are skillfully predicted in the North Atlantic and the Northwestern Pacific, with a strong modulation by the El Nino‐Southern Oscillation. Plain Language Summary: In this study, we examine the subseasonal (2–12 weeks) prediction of tropical cyclones (TCs) in the Community Earth System Model version 2 (CAM6) subseasonal prediction system. We evaluate the modeled TC climatological characteristics—including storm frequency, spatial distribution, and seasonality—and the model's skill in forecasting weekly TC genesis in each TC basin. We find that the model skillfully captures the observed basin‐wide climatological TC seasonality and spatial distributions, but TC genesis is largely underestimated from week 2 onward. For some basins and lead times, the predicted TC genesis is primarily controlled by the number of preexisting disturbances (TC "seeds") and the mean‐state climate condition. The model has good prediction skill compared with the constant climatology across all the basins and lead times but has limited skill in predicting deviations from the TC seasonal cycle. We find that the Madden‐Julian Oscillation has a strong modulation on TC activity and provides the main source of predictability for subseasonal TC genesis. The interannual variability of predicted TC activity is skillfully predicted in the North Atlantic and the Northwestern Pacific, with a strong modulation by the El Nino‐Southern Oscillation. Key Points: Subseasonal reforecasts of tropical cyclone genesis from the Community Earth System Model version 2 (CESM2) (CAM6) subseasonal prediction system are examinedCESM2 has good prediction skill relative to the constant climatology but has limited skill in predicting deviations from the seasonal cycleThe predicted tropical cyclone (TC) genesis is controlled by the frequency of TC seeds and the mean‐state climate condition for some lead times and basins [ABSTRACT FROM AUTHOR]

The representativeness of surface solar radiation (SSR) point observations is an important issue when using them in combination with gridded data. We conduct a comprehensive near‐global (50°S to 55°N) analysis on the representativeness of SSR point observations on the monthly mean time scale. Thereto, we apply the existing concepts of decorrelation lengths (δ), spatial sampling biases (β), and spatial sampling errors (ε) to three high‐resolution gridded monthly mean SSR data sets (CLARA, SARAH‐P, and SARAH‐E) provided by the Satellite Application Facility on Climate Monitoring. While δ quantifies the area for which a point observation is representative, β and ε are uncertainty estimates with respect to the 1‐degree reference grid (G). For this grid we find a near‐global average δG=3.4°, βG=1.4 W/m2, and εG=7.6 W/m2 with substantial regional differences. Disregarding tropical, mountainous, and some coastal regions, monthly SSR point observations can largely be considered representative of a 1‐degree grid. Since ε is an uncorrectable error the total uncertainty when combining point with 1‐degree gridded data is roughly 40% higher than the uncertainty of station‐based SSR measurements alone if a rigorous bias correction is applied. Cloud cover and terrain data can at maximum explain 50% of the patterns of the representativeness metrics. We apply our methodology to the stations of the Baseline Surface Radiation Network. Overall, this study shows that representativeness is strongly dependent on local conditions and that all three metrics (δ, β, and ε) must be considered for a comprehensive assessment of representativeness. Plain Language Summary: Station‐based observations are the most robust way to measure the amount of solar radiation reaching the Earth's surface (surface solar radiation [SSR]). These measurements are point observations yet are often used in combination with satellite or model data (e.g., for validation or for derivation of other quantities). The latter have a typical spatial extent up to a few hundred kilometers. Thus, it is important that the point observations are representative of this large area. In this paper, we show that the representativeness of SSR point observations varies regionally and is strongly dependent on local conditions. We find that some regions are problematic in terms of representativeness. However, in most regions SSR point observations can be considered representative for a 1‐degree grid. We quantified additional uncertainties, which have to be taken into account when combining point and gridded data. Key Points: Representativeness of monthly SSR point observations is assessed near globally with three metricsPoint and 1‐degree gridded data can be combined, except near coasts, mountains, and in the tropicsCombined uncertainties vary strongly with region and exceed measurement uncertainties by on average 40% [ABSTRACT FROM AUTHOR]

Analyses of the thermodynamics of precipitating clouds are mostly based on localized in situ campaigns or, more globally, weather analyses and reanalyses. This work presents a comparison of weather analyses to satellite observations and a radiometeorological method that shows how precipitating layers inside clouds coincide with weather analyses underestimates of the amount of water vapor. The thermodynamic information from inside precipitating clouds is extracted using observed radio occultation (RO) refractivity profiles without requiring weather analysis input, thus reducing analysis‐induced biases. The radiometeorological method is described by first identifying the differences between adiabatically dry, mixing‐ratio conserving, and saturated pseudoadiabatic refractivity profiles. These reference profiles are then compared to observed RO refractivity profiles within precipitating and nonprecipitating clouds to infer changes in their height‐dependent thermodynamic states and in stability to convection. Precipitation is found to start below layers close to pseudoadiabatic and precipitation layers coincide with changes into conditional stability against convection. A statistical comparison between observed profiles and the gradients predicted for a saturated pseudoadiabatic profile is made and finds that on the global average, precipitation separates clouds from the Clausius‐Clapeyron law and profiles are close to a saturated pseudoadiabat. The results (a) help constrain the physical processes associated to precipitation inside clouds and (b) validate the potential of graphical RO techniques to analyze observations without ancillary temperature data from weather analyses. Plain Language Summary: Predicting how precipitation responds to changes in atmospheric thermal profiles remains a challenge identified by the Intergovernmental Panel on Climate Change. Solving this challenge requires comparing models with the observed thermodynamics of precipitating clouds. Only radio occultation (RO) can constraint globally the thermodynamics inside clouds with high vertical resolution. Infrared and microwave can measure the thermodynamics outside and only partially clouds, and radar instruments that measure inside clouds do not provide thermodynamic information.This paper develops a method to use RO for distinguishing the thermodynamics inside precipitating versus nonprecipitating clouds. The identification of rain is made using coincidences of RO soundings with Tropical Rainfall Measuring Mission and CloudSat observations. Using the method, we show that globally, (1) the European Center for Medium‐Range Weather Forecast ERA Interim reanalysis and the Global Forecast System weather analysis have a global bias in precipitating clouds caused by misrepresentation of the thermodynamics inside clouds; (2) the nature of the bias is associated to a misrepresentation of the lapse rates by the analyses; (3) there are changes in stability to moist convection associated to the height where precipitation originates, and (4) the transition from midtropospheric lapse rates to boundary layer shows more frequent sharp inversions in nonprecipitating than in precipitating scenes. Key Points: Model‐independent analyses of radio occultation, RO, are developed to constrain lapse rates and stability inside cloudsRO observes how precipitation changes layerwise the lapse rates that define stability to convection in ways missed by weather analysesTop of boundary layer inversions leading to refractivity gradients is sharper in nonprecipitating than precipitating scenes [ABSTRACT FROM AUTHOR]

Enhancement of precipitation processes aloft over complex terrain is documented using reflectivity data from an S‐band scanning radar (NPOL) that was deployed on the west coast of Washington State during the Olympic Mountains Experiment (OLYMPEX). From November 2015 through mid‐January 2016, NPOL obtained high‐resolution data within sectors over the ocean and over the windward slopes of the Olympic Mountains. Contoured Frequency by Altitude Diagrams of radar reflectivity highlight a higher frequency of occurrence of larger reflectivities for all heights between 2 and 8 km over land compared to ocean, with the largest difference in the 4‐ to 6‐km range indicating a robust signature of enhancement aloft over the windward slopes. This enhancement pattern is found to some degree under all environmental conditions considered but is especially pronounced during periods of high vapor transport, high melting level height, southwest low‐level winds, and neutral stability. These conditions are generally associated with warm sectors of midlatitude cyclones and atmospheric rivers. Past studies have postulated that a secondary enhancement in reflectivity aloft was an intrinsic part of atmospheric river type systems. However, these results show that further significant enhancement of this signature occurs as deep moist‐neutral, high water vapor content flow is lifted when it encounters a mountain range. Reflectivity data from the dual‐precipitation radar aboard the Global Precipitation Measurement satellite also documents this reflectivity increase aloft over the Olympic Mountains compared to the adjacent ocean, showing the potential for Global Precipitation Measurement to provide reliable estimates of precipitation structure over remote mountainous regions. Plain Language Summary: When frontal cyclones pass over a mountain range, modification of flow often results in precipitation enhancement on the windward slopes. Most studies of this phenomenon rely on the precipitation patterns deduced from surface networks of rain gauges or through numerical modeling. Little attention has been given to orographic modification of the precipitation processes occurring in the middle and upper layers of clouds. This paper uses high‐resolution vertical cross sections of radar reflectivity data taken during the Olympic Mountains Experiment. Measurements made over the ocean are compared to those over the windward slopes of the Olympic Mountains and a clear signature of enhancement aloft over the windward slopes is found at all heights from 2 to 8 km strongest between 4 and 6 km. This enhancement of reflectivity aloft is especially pronounced under environmental conditions of large water vapor transport, high melting level, strong onshore‐directed low‐level winds and neutral stability. Those environmental conditions are commonly found in warm sectors of midlatitude cyclones and in atmospheric river‐type events. This same signature of higher reflectivity aloft over windward slopes is found from satellite‐derived radar reflectivity measurements implying that satellites have the potential to provide reliable estimates of precipitation structure over remote mountainous regions. Key Points: Enhancement of precipitation processes is found in radar reflectivity data above the melting level over complex terrainEnhancement aloft is especially pronounced during periods of high vapor transport, onshore flow, and neutral low‐level static stabilitySatellite‐borne radar detects this enhancement so that reliable estimates of precipitation over remote mountain regions are possible [ABSTRACT FROM AUTHOR]

Satellite lidar remote sensing of the atmosphere has been ongoing for more than a decade providing the opportunity to study atmospheric processes in great detail. Here we use 12 years of Cloud‐Aerosol Lidar with Orthogonal Polarization measurements to derive a climatology of blowing snow layer height, optical depth, and frequency over Antarctica for the period 2006–2017. Limited to the vertical resolution of the Cloud‐Aerosol Lidar with Orthogonal Polarization data, our climatology includes all blowing snow layers greater than about 30 m in thickness for clear or optically thin cloud regions. Our results show that blowing snow occurs over 50% of the time over large regions with frequencies often exceeding 70%. The overall pattern of blowing snow frequency is fairly consistent from year to year, but there are regional differences. We examined the data for temporal trends in blowing snow properties and found significant trends only in blowing snow frequency. A small area of East Antarctica with generally low blowing snow frequency shows a statistically significant increase in blowing snow frequency ranging from 10% to 100% per decade. No significant trends in frequency were found in regions of high (>50%) blowing snow frequency, and only isolated small areas exhibited a decrease in frequency through the study period. Plain Language Summary: During the last decade a new satellite remote sensing tool has become available for atmospheric research. The technique, called lidar (light ranging and detection), uses short (laser) pulses of visible light to probe the vertical structure of the atmosphere. The Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations mission launched in 2006 has greatly increased our knowledge of atmospheric structure over the polar region. One of the important discoveries made by this satellite is the ubiquitous nature of blowing snow episodes over Antarctica. Blowing snow occurs when the surface wind exceeds a threshold value (about 5–7 m/s) and snow is carried aloft and transported downwind. Once aloft, the snow particles can be carried great distances and even blown off the continent. In this paper we use Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation data to detect the occurrence of blowing snow over Antarctica and construct a 12‐year climatology of its frequency of occurrence, layer depth, and particle density. We have discovered that many regions of Antarctica experience blowing snow over 70% of the time and that blowing snow storms can last for days, cover areas as large as the state of Texas, and reach heights of 400 m or more. Key Points: A first satellite‐derived climatology of blowing snow over Antarctica is presentedBlowing snow frequency exceeds 70% over large regions of East AntarcticaSome areas of East Antarctic show a statistically significant increasing trend in blowing snow frequency [ABSTRACT FROM AUTHOR]

Solar radiation received at the Earth's surface (Rs) is comprised of two components, the direct radiation (Rd) and the diffuse radiation (Rf). Rd, the direct beam from the sun, is essential for concentrated solar power generation. Rf, scattered by atmospheric molecules, aerosols, or cloud droplets, has a fertilization effect on plant photosynthesis. But how Rd and Rf change diurnally is largely unknown owing to the lack of long‐term measurements. Taking advantage of 22 years of homogeneous hourly surface observations over China, this study documents the climatological means and evolutions in the diurnal cycles of Rd and Rf since 1993, with an emphasis on their implications for solar power and agricultural production. Over the solar energy resource region, we observe a loss of Rd which is relatively large near sunrise and sunset at low solar elevation angles when the sunrays pass through the atmosphere on a longer pathway. However, the concentrated Rd energy covering an average 10‐hr period around noon during a day is relatively unaffected. Over the agricultural crop resource region, the large amounts of clouds and aerosols scattering more of the incoming light result in Rf taking the main proportion of Rs during the whole day. Rf resources and their fertilization effect in the main crop region of China further enhances since 1993 over almost all hours of the day. Key Points: The loss of direct radiation over China since 1993 is relatively large at sunrise and sunset with little effect on solar power generationThe diffuse component dominates solar radiation normally near sunrise and sunset, but for the whole day over the main sown area of ChinaThe diffuse fraction is further enhanced in the main sown area of China over almost all hours of the day since 1993 [ABSTRACT FROM AUTHOR]

Eastern China is perennially hit by mesoscale convective systems (MCSs), yet it remains an open question as to whether and how their general properties change throughout the annual cycle. By leveraging high‐resolution satellite observations and a hybrid tracking algorithm, we present a 20‐year (2001–2020) climatology of MCSs over eastern China during eight subseasonal‐to‐seasonal (S2S) monsoon stages. MCSs contribute up to 50% of the stage‐total precipitation and over 60% of the rainband‐zone precipitation during the Pre‐Meiyu and Meiyu episodes, and their contributions remain non‐trivial during the transition seasons. We discover two contrasting regimes of MCSs that alternate immediately upon the Pre‐Meiyu and the Fall onsets. The wintertime regime features fast‐propagating shallow systems initiated at night in a strongly sheared and dry environment. The summertime regime, instead, features an outbreak of MCSs in the south, where the systems often initiate in the afternoon and propagate 2–3 times slower than the cold‐season ones. Based on multivariate clustering analysis, the nighttime MCSs that dictate the winter stages often initiate over a deep nocturnal boundary layer with moist rear inflows upgliding above it. In contrast, the afternoon‐initiated MCSs under the summertime regime feature a pronounced convective available potential energy (CAPE) "tongue" and upslope flows in their southeast quadrant. The southwesterly moist ascending flows are likely to shallow the convective inhibition at the tip of the CAPE tongue and facilitate the intense updrafts of the MCSs. Findings here may offer insights into S2S weather prediction and facilitate agricultural and water management throughout the year. Plain Language Summary: Eastern China has been one of the worst‐hit regions globally by extreme precipitation and floods. Many of these hazards result from intense and well‐organized rainstorms, also known as mesoscale convective systems (MCSs), typically lasting for several hours with a horizontal scale of 100 km or larger. Despite numerous case studies on their evolution and dynamics, the annual cycle of the impacts and properties of MCSs is yet to be fully understood. Using high‐resolution satellite observations and a hybrid tracking algorithm, we present a 20‐year (2001–2020) climatology of MCSs in eight monsoon stages year‐round. We discover a dual regime wherein two distinct regimes of MCS characteristics are observed throughout the annual cycle. It turns out that MCSs can contribute up to 50% of the stage‐total precipitation and over 60% of the rainband‐zone precipitation during the pluvial episodes, and their contributions remain non‐trivial during the transition seasons. The prevailing environmental conditions at the initiation of MCSs are revealed and discussed. Findings from the present study help broaden our understanding of the annual cycle of MCSs and may offer insights into numerical weather simulations and prediction, water and agricultural management, and disaster risk reduction in eastern China. Key Points: An unprecedented monsoon‐annual‐cycle climatology of mesoscale convective systems (MCSs) in eastern ChinaDiscovery of two contrasting regimes of MCSs that alternate upon the Pre‐Meiyu and Fall onsetsMoist rear inflows, static instability, upslope flows, and cold pool‐shear interactions are recurring in convective initiation [ABSTRACT FROM AUTHOR]

Investigated in this study are the seasonal and semi‐diurnal variations of the cloud‐phase climatology over the southern Himalayas and adjacent regions by using 5 years of Himawari‐8 cloud‐product data (2016–2020). The four selected regions from south to north are the Gangetic Plains (I), Himalayan foothills (II), southern slope of the Himalayas (III), and the Himalayan–Tibetan Plateau region (IV), respectively. Results showed that the cloud frequency of cloud gradually increases from region I via II to III, then sharply decreases as the altitude increases up to IV. Ice‐phase clouds occurs more frequently over regions I/II (III/IV) during boreal summer (winter), while water‐phase cloud has a higher frequency over region III/IV (I/II) in summer (winter), respectively. All of the different cloud phases have a clear seasonal cycle. Furthermore, the semi‐diurnal variation shows that water‐phase clouds tends to have an occurrence frequency peak around noon (in the later afternoon) over regions I/II/III in summer (winter), whereas over region IV it only occurs more in the morning in both seasons. Ice‐phase cloud generally occurs more in the late afternoon in both boreal summer and winter, especially over region IV. Further analysis showed that the differences in the cloud‐phase characteristics over the southern Himalayas and adjacent regions are likely related to the interactions of the synoptic‐scale circulation, the topography, and the water vapor transport. Plain Language Summary: By using 5 years geostationary weather satellite cloud product, we investigated the seasonal and semi‐diurnal variations of the cloud‐phase climatology characteristics over the southern Himalayas and adjacent regions, including four select sectors of the plain, foothill, slope and plateau. We found that the cloud frequency gradually increases from plain via foothill to slope, then decreases as the terrain increases up to plateau. All different phase clouds have a clear seasonal cycle and semi‐diurnal variations. Such as ice‐phase cloud occurs more over the plain and the foothill during summer season, while it occurs more over the slope region and plateau in winter; water‐phase cloud has a peak at noon (later afternoon) over the plain/foothill/slope in summer (winter), while over the plateau, it only occurs more in the morning. The results are important for comprehend how the southern Himalayas impact regional climate. Key Points: Cloud frequency increases significantly from region I via II to III, then decreases as the elevation further increases up to region IVIce‐phase clouds occurs more frequently over regions I/II (III/IV) in summer (winter), which is opposite to the occurrence of water‐phase cloudWater‐phase clouds tend to occur more around noon (in the later afternoon) over regions I/II/III in summer (winter), while it only occurs more in the morning over region IV [ABSTRACT FROM AUTHOR]

Utilizing 956 nights of Na lidar nocturnal mesopause region temperature profiles acquired at Fort Collins, CO (40.6°N, 105.1°W) over a 20‐year period (March 1990–2010), we deduce background nightly mean temperature T¯(z) $\bar{T}(z)$ and the square of the buoyancy frequency N2(z) at 2‐km resolution between 83 and 105 km. The temperature climatology reveals the two‐level mesopause structure with clarity and sharp mesopause transitions, resulting in 102 days of summer from Days 121 to 222 of the year. The same data set analyzed at 10‐min and 1‐km resolution gives the gravity wave (GW) temperature perturbations Ti'(z) and the wave variance Var(T′(z)) and GW potential energy Epm(z) between 85 and 100 km. Seasonal averages of GW Var(T′(z)) and Epm(z) between 90 and 100 km, show that Var(T′) for spring and autumn are comparable and lower than for summer and winter. Due mainly to the higher background stability, or larger N2(z) in summer, Epm(z) between 85 and 100 km is comparable in spring, summer, and autumn seasons, but ∼30%–45% smaller than the winter values at the same altitude. The uncertainties are about 4% for winter and about 5% for the other three seasons. The values for Epm are (156.0, 176.2, 145.6, and 186.2 J/kg) at 85 km for (spring, summer, autumn, and winter) respectively, (125.4, 120.2, 115.2, and 168.7 J/kg) at 93 km, and (207.5, 180.5, 213.1, and 278.6 J/kg) at 100 km. Going up in altitude, all profiles first decrease and then increase, suggesting that climatologically, GWs break below 85 km. Key Points: With 956 nights of observations, we revisit the climatology of the background temperature and study seasonal gravity wave (GW) activitiesSharp transitions are found at Days 121 and 222 between the higher radiation‐driven and the lower dynamic‐driven mesopauses at 40.6°NThe winter GW potential energy is ∼40% higher than other seasons. Climatologically, their profiles suggest wave breaking below 85 km [ABSTRACT FROM AUTHOR]

Land surface albedo plays a critical role in climate, hydrological and biogeochemical modeling, and weather forecasting. It is often assigned in models and satellite retrievals by albedo climatology look‐up tables using land cover type and other variables; however, there are considerable differences in albedo simulations among models, which partially result from uncertainty in obsolete albedo climatology. Therefore, this study introduces a new global 500 m daily blue‐sky land surface albedo climatology data set under both actual and snow‐free surface conditions utilizing 20‐year Moderate Resolution Imaging Spectroradiometer products from Google Earth Engine. In situ measurements from 38 long‐term‐maintained sites were utilized to validate the accuracies of different albedo climatology datasets. The root‐mean‐square error, bias, and correlation coefficient of the new climatology are 0.031, −0.003, and 0.96, respectively, which are more accurate than the Global Land Surface Satellite, GlobAlbedo, and 16 model datasets. Data intercomparison suggests that ERA5 exhibits better performance than Modern‐Era Retrospective Analysis for Research and Applications Version 2 (MERRA2) and 14 Coupled Model Intercomparison Projects Phase 6 models. However, it contains positive biases in the snow‐free season, while MERRA2 underestimates the snow albedo. Global albedo variation associated with basic surface plant functional types was also characterized, and snow impact was considered separately. Temporal variability analysis indicates that traditional climatology datasets with coarser temporal resolutions (≥8 days) cannot capture albedo variation over areas with distinct snow seasons, especially in central Eurasia and boreal regions. These results confirm the high reliability and robustness of the new albedo climatology in model assessment, data assimilation, and satellite product retrievals. Plain Language Summary: Surface albedo represents the Earth's surface ability to reflect solar energy, and thus directly influences atmospheric and water circulations by controlling available energies. As an essential variable estimated in current climate models, surface albedo is assigned by searching look‐up tables based on the land cover and soil types. However, there are large differences in simulated albedo among various models, partially because the albedo climatology in these tables was generated in the 1980s and needs to be updated. As global surface albedo has been accurately retrieved from satellite data for decades, we were able to produce a new albedo climatology data set under actual and snow‐free conditions with high spatiotemporal resolutions. Ground validation and data comparison indicate that the new data set performs with higher accuracy compared with other datasets. Moreover, assessment by the new climatology data set shows that albedo from advanced climate models and reanalysis datasets has clear uncertainties, especially over high latitudes and the Tibetan Plateau. Temporal variation in global albedo is better characterized at basic vegetation types. The new albedo climatology data set shows great potential for use in model assessment, modeling improvement, and satellite retrieval of other variables. Key Points: A global 500 m daily blue‐sky land surface albedo climatology data set in actual and snow‐free surface conditions was produced from Moderate Resolution Imaging SpectroradiometerSite validation and data comparison reveal its reliability and robustness in model assessment, data assimilation, and satellite retrievalsSimulated albedo data by state‐of‐art reanalysis and Coupled Model Intercomparison Projects Phase 6 models still have a clear bias in polar regions and the Tibetan Plateau [ABSTRACT FROM AUTHOR]

Atmospheric mineral dust deposition plays an important role in providing nutrients to marine ecosystems. In this study, the climatology of dust deposition in the Adriatic Sea area was determined for the first time based on Modern‐Era Retrospective Analysis for Research and Applications, version 2 reanalysis from 1989 to 2019. The annual cycle of deposition exhibits two maxima: a stronger maxima in March–April and a weaker maxima in November. Wet deposition is a dominant process with a relative contribution to overall deposition from 67.35% to 88.53%. Deposition hot spots are along the Montenegrin coast and Otrant. The average contribution of dust deposition events (DDEs) is 16.5% (60.2 dy yr−1), with the strongest deposition during 1999–2009 and a positive trend in deposited mass during the study period. The effect of dust deposition on primary production is observed by a high level of oxygen saturation up to 250% (usually it is lower, up to 150%) in the stratified middle water layer (5–8 m) of the central Adriatic marine system (Rogoznica Lake) during an intense wet deposition episode. Such extreme values of oxygen saturation can be taken as an indication of biological activity related to an increase in phytoplankton abundance and activity, diatoms in particular. Key Points: Desert dust deposition annual cycle in the Adriatic Sea is bimodalEmpirical orthogonal functions reveal the strongest deposition related to Mediterranean cyclones in springHigh oxygen production in Rogoznica Lake marine system is related to dust deposition events [ABSTRACT FROM AUTHOR]

Studies of land‐atmosphere interactions under a clear sky and low cumulus cloud conditions are common from long‐term observatories like at the southern great plains. How well the relationships and responses of surface radiative and turbulent heat fluxes determined from these investigations hold for more heterogeneous surfaces in other climate regimes, however, is uncertain. In this study, detailed observations of the surface energy budget and daytime boundary layer properties are analyzed using measurements from the Chequamegon Heterogenous Ecosystem Energy‐Balance Study Enabled by a High‐Density Extensive Array of Detectors 2019 (CHEESEHEAD19) field campaign, July‐October 2019, across a heterogeneous forested landscape of northern Wisconsin. A cloud regime framework is employed to classify consecutive periods of clear skies from lower atmosphere stratiform and cumulus clouds. A seasonal transition from low cumulus to low stratiform periods occurred, together with a diurnal pattern in cloudy or clear sky period dominance. Radiative forcing was highly dependent on sky conditions, leading to changes in the redistribution efficiency of radiative energy by the surface turbulent heat fluxes. During CHEESEHEAD19, small Bowen ratios dominated with daytime latent heat fluxes three times as large as sensible heat fluxes for all sky conditions studied; the forested region, therefore, falls within an energy‐limited regime. The depth of the daytime mixed layer depended upon the sky condition and thermodynamic setting; deeper mixed layers occurred during periods of low cumulus and not clear skies. Profiles of vertical velocity were found to have enhanced variance under low cumulus compared to clear sky periods, suggesting potential for cloud feedbacks on boundary layer structure and surface energy fluxes. Plain Language Summary: This study investigates how different cloud regimes influence the exchange of energy at Earth's surface over a highly heterogeneous forested landscape in northern Wisconsin. Clouds directly modify the solar and infrared radiation reaching the surface. In turn, the modifications to radiation affect how turbulence near the surface is generated and its magnitude. The net result of these energy fluxes determines the warming and cooling processes at the surface, with direct implications on the development of local weather systems. From the observations in northern Wisconsin, an apparent partition in energy fluxes between two commonly observed lower atmosphere cloud types is found. A seasonal pattern in the occurrence of these cloud types was observed. Because of these cloud‐specific preferences, turbulence generated near the surface was larger during the first half of the 3‐month field campaign. Enhanced surface fluxes supported a deeper boundary layer for the shallow cumulus cloud conditions compared to overcast conditions. These fluxes were even larger than periods when skies were clear; however clear sky conditions were most frequent during the morning when surface energy fluxes were generally increasing with time during this development stage of the convective mixed layer. Turbulent fluxes associated with evaporation at the surface dominated over dry fluxes, regardless of the overhead sky conditions. These findings represent important differences to heavily study climatological regions where grasslands make up the primary surface characteristics. Key Points: Detailed surface energy fluxes and boundary layer structure responses to three boundary layer sky conditions are examined: low stratiform, low cumulus, clearTurbulent and radiative flux relationships were separable by cloud regime; latent fluxes dominated over sensible fluxes by a factor of 3 (low Bowen ratios dominated)Boundary layers were deeper during low cumulus compared to clear sky periods; surface‐atmosphere interactions are complex over the heterogenous forest landscape [ABSTRACT FROM AUTHOR]

Most existing cloud models tend to overestimate the size of cloud ice particles and underestimate their concentration. This emphasizes the need to provide a reliable observational reference to optimize cloud model performance, particularly in areas of high concentration of ice at high altitudes. The dual‐polarization radars give the community a unique opportunity to quantify cloud ice with a good accuracy using polarimetric radar retrievals. In this study, we utilize the network of operational WSR‐88D radars to build a climatology of the vertical profiles of radar variables, such as radar reflectivity Z, differential reflectivity ZDR, and specific differential phase KDP as well as the radar‐retrieved vertical profiles of ice water content (IWC) above the melting layer and liquid water content below it, mean volume diameter Dm, and total number concentration Nt of ice and liquid particles. Such climatology was created for continental/marine mesoscale convective systems (MCSs) and tropical cyclones including hurricanes. The dataset includes 13 continental MCSs, 10 marine MCSs, and 11 tropical cyclones. Separate statistics of the "background" vertical profiles and the ones associated with high IWC aloft have been obtained in the course of this study. It is shown that continental MCSs exhibit larger size of ice in lower concentration aloft compared to the marine MCSs and especially tropical cyclones/hurricanes. A combination of high KDP and low Z aloft signifies lower Dm, higher Nt, and often substantial IWC. Key Points: Climatology of the vertical profiles of polarimetric radar variables and microphysical parameters is documented for different storm typesAreas of high ice water content (IWC) in clouds are characterized by high values of specific differential phase combined with low reflectivityTropical clouds have smaller size ice in higher concentration compared to their continental counterparts with comparable IWC [ABSTRACT FROM AUTHOR]

In the mesosphere and lower thermosphere (MLT) region, residual circulations driven by gravity wave breaking and dissipation significantly impact constituent distribution and the height and temperature of the mesopause. The distribution of CO2 can be used as a proxy for the residual circulations. Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) CO2 volume mixing ratio (VMR) and temperature measurements from 2003 to 2020 are used to study the monthly climatology of MLT residual circulations and the mesopause height. Our analyses show that (a) mesopause height strongly correlates with the CO2 VMR vertical gradient during solstices; (b) mesopause height has a discontinuity at midlatitude in the summer hemisphere, with a lower mesopause height at mid‐to‐high latitudes as a result of adiabatic cooling driven by strong adiabatic upwelling; (c) the residual circulations have strong seasonal variations at mid‐to‐high latitudes, but they are more uniform at low latitudes; and (d) the interannual variability of the residual circulations and mesopause height is larger in the Southern Hemisphere (SH; 4–5 km) than in the Northern Hemisphere (NH; 0.5–1 km). Key Points: Monthly climatology of the mesopause height, and MLT CO2 gradients as signatures of the residual circulations are derived from SABER dataBoth the regions of maximum vertical CO2 gradients and mesopause height show strong seasonal variations at mid‐to‐high latitudesInterannual variations of the height of maximum vertical CO2 gradients and mesopause height are larger in the SH than in the NH [ABSTRACT FROM AUTHOR]

The Southern Ocean has absorbed most of the excess heat associated with anthropogenic greenhouse gas emissions. Since Southern Ocean observations are sparse in certain regions and seasons, much of our knowledge of ocean heat uptake is based on climate model simulations. However, climate models still inadequately represent some properties of Southern Ocean clouds, and they have not identified the mechanisms by which clouds may affect Southern Ocean heat uptake (SOHU). Here, we use the ERA5 and JRA‐55 reanalyses to assess the influence of clouds and other atmospheric processes on SOHU from 1979 to 2020. We find that years with the highest SOHU between 45° and 65°S are dominated by ocean heat uptake anomalies during winter and spring, but not during summer or fall. Winter and spring cloud cover are up to 7% higher when SOHU is up to 5.5 W/m2 higher than the climatological seasonal mean, with the largest increases in the South Pacific Ocean. Clouds also contain more liquid water. These changes in cloud properties increase downwelling longwave radiation, amplifying ocean heat uptake. Cloud changes are also concomitant with a more stable lower atmosphere, which suppresses turbulent heat fluxes out of the surface. Overall, we find that SOHU is likely not mediated by enhanced surface shortwave absorption over the observational time period. A better understanding of how atmospheric processes impact ocean heat uptake may help improve our understanding of ocean heat uptake mechanisms in the current generation of climate models. Key Points: Anomalously strong annual mean Southern Ocean heat uptake is mainly controlled by reduced ocean heat loss during winterChanges in clouds and their associated atmospheric states amplify ocean heat uptake by increasing downward longwave radiation at the surfaceMore clouds are linked to a more stable atmosphere which increases ocean heat uptake by suppressing turbulent heat fluxes out of the surface [ABSTRACT FROM AUTHOR]

In this study, the landfalling tropical cyclone (TC) exposure in Southeast Asia for a 50‐year period from 1970 to 2019 is investigated relative to the total western North Pacific (WNP) climatology taking disparities in historical records into account. Long‐term trends in landfalling TCs are analyzed and intercompared among the Regional Specialized Meteorological Center of Tokyo (TOKYO), China Meteorological Administration (CMA), Hong Kong Observatory (HKO), and Joint Typhoon Warning Center (JTWC) best track datasets. Interannual and intra‐seasonal variations are further examined by sub‐region and nation using JTWC records. Approximately half of the WNP TCs make landfall in Southeast Asia representing over 75% of the total WNP landfalls in all datasets. Over the study period, there is a slight upward trend in landfalling TC frequency in both the WNP and Southeast Asia in the JTWC dataset, while the number of landfall events has decreased in the CMA and TOKYO datasets. A consistent northward shift in landfalling locations over the 50‐year period is found in all datasets such that landfalls have decreased in the Philippines, Vietnam, but increased in some South China areas. The TOKYO dataset alone suggests that landfalling TCs in South China have slowed down over the study period, which would increase rainfall and wind risks in their path if substantiated. Less TC landfalls occur in El Niño years with landfalling locations shifting northwestward over the Asian mainland, while landfalls are higher and more distributed in La Niña, and highest in Neutral years. Key Points: Approximately half of all Western North Pacific tropical cyclones made landfall in Southeast AsiaA northward shift of landfalling locations is found in all four agency best track recordsLandfalls are lower and shifted northwestward in El Niño, higher and more distributed in La Niña, and highest in Neutral years [ABSTRACT FROM AUTHOR]

Fram Strait in the northern North Atlantic is a key region for marine cold air outbreaks (MCAOs), southward discharges of polar air under northerly air flow, which have a strong impact on air‐sea heat fluxes, boundary layer processes and severe weather. This study investigates climatologies and decadal trends of Fram Strait MCAOs of different intensity classes based on the ERA5 reanalysis product for 1979–2020. Among striking interannual variability, it is shown that the main MCAO season is December through March, when MCAOs occur around 2/3 of the time. We report on significant decadal MCAO decreases in December and January, and a significant increase in March. While the mid‐winter decrease is mainly related to the different paces of warming between the surface and the lower atmosphere, the increase in March can be related to changes in synoptic circulation patterns. As an explanation for the latter, a possible feedback between retreating Barents Sea sea ice, enhanced cyclonic activity and Fram Strait MCAOs is postulated. Exemplifying the trend toward stronger MCAOs during March, the study details the recordbreaking MCAO season in early 2020, and an observational case study of an extreme MCAO event in March 2020 is conducted. Thereby, radiosonde observations are combined with kinematic air back‐trajectories to provide rare observational evidence for the diabatic cooling and drying during the MCAO preconditioning phase. Key Points: 1979–2020 climatology of marine cold air outbreaks (MCAOs) in Fram StraitSignificant MCAO increase in March is dynamically driven; significant decrease in mid‐winter due to vertical distribution of warmingAnomalous circulation in February/March 2020 yields extreme MCAO season with observed air mass preconditioning [ABSTRACT FROM AUTHOR]

Observational records are more often than not influenced by residual non‐climatic factors which must be detected and adjusted for prior to their usage. In this work, we present a novel approach, named Radiosounding HARMonization (RHARM), providing a homogenized data set of temperature, humidity and wind profiles along with an estimation of the measurement uncertainties for 697 radiosounding stations globally. The RHARM method has been used to adjust twice daily (0000 and 1200 UTC) radiosonde data holdings at 16 pressure levels in the range 1,000–10 hPa, from 1978 to present, provided by the Integrated Global Radiosonde Archive. Relative humidity (RH) data are limited to 250 hPa. The applied adjustments are interpolated to all reported levels. RHARM is the first data set to provide homogenized time series with an estimation of the observational uncertainty at each sounding pressure level. By construction, RHARM adjusted fields are not affected by cross‐contamination of biases across stations and are fully independent of reanalysis data. Analysis of trends for temperature, RH and winds highlights increased geographical coherency of trends over 1978–2000 globally, but especially in the Northern Hemisphere and South America. RHARM shows warming trends of 0.39 K/decade at 300 hPa in the Northern Hemisphere and of 0.25 K/decade in the tropics. The RHARM adjustments also reduce differences with the European Centre for Medium‐Range Weather Forecast ERA5 reanalysis, with the strongest effect in the Northern Hemisphere for temperature and relative humidity. For wind speed, the comparison indicates a good agreement with ERA5 in the troposphere. Plain Language Summary: Systematic observations of atmospheric parameters by balloon soundings have been collected regularly across the globe since decades. However, changes in the instrumentation, calculation algorithms, station re‐locations and other factors can influence the measurement time series, making the identification of climate signals difficult. The availability of measurement metadata, cross‐comparison with (sparser) reference networks and the application of statistical methods allows to greatly improve the physical consistency of the records. We developed the Radiosounding HARMonization (RHARM) methodology to provide users with homogenized radiosonde profiles of temperature, humidity, and wind, along with measurement uncertainties, for 697 locations globally and twice daily based on the Integrated Global Radiosonde Archive. Key features of RHARM are the provision of multiple fundamental atmospheric parameters, adjusted for spurious biases and the inclusion of measurement uncertainties estimated following the standards of the metrological community when available metadata permits. The current version of the RHARM data set can be used to investigate tropospheric weather and climate for the last four decades. Key Points: The Radiosounding HARMonization (RHARM) data set provides homogenized time series of temperature, relative humidity and wind profiles for hundreds of radiosonde stationsMetrologically accurate estimates of the observational uncertainty are provided together with each observation and variableFor all variables, RHARM increases the geographical coherency of estimated trends and the agreement with a modern atmospheric reanalysis [ABSTRACT FROM AUTHOR]

Natural climate variability poses a limit to the confidence in regional climate projections, particularly for the near‐term. Therefore, the next decades are of importance for regional impact studies and the development of regional adaptation plans. This article presents results from an ensemble of regional climate model simulations (years 1996–2005 and 2026–2035) that are used to examine the effects of both anthropogenic forcing and natural variability associated with the Pacific Decadal Oscillation (PDO) on near‐term climate projections for the Hawaiian Islands. The Community Earth System Model Large Ensemble (CESM‐LE) is used in conjunction with the Weather Research and Forecasting (WRF) model for downscaling. The climate responses to the PDO and anthropogenic forcing are isolated and analyzed separately. In response to anthropogenic forcing, significant increases in surface air temperature, of ∼0.8 K, are projected at low elevations. Stronger warming, of up to 1.3 K, is seen at higher elevation areas. Future climate simulations show significant increases in wet season rainfall, of ∼10%–20%, along the windward slopes of Big Island and Maui. Rainfall patterns during the positive PDO phase are projected to reverse in sign, leading to drier conditions, by ∼10%–30%, at many locations. Future climate simulations show daily rainfall extremes will increase, by up to ∼10%–15%, at many locations. Daily temperature extremes are also projected to increase significantly, by up to 1.4 K. Overall, results indicate that natural variability will continue to contribute to uncertainty in near‐term rainfall projections for the Hawaiian Islands, masking the forced signal. Plain Language Summary: This project studies how temperature and precipitation will change across the Hawaiian Islands in the near future due to human‐induced causes (e.g., burning coal and other fossil fuels). This is done by comparing climate model simulations for two 10‐year periods (1996–2005 vs. 2026–2035). Further, this research evaluates how natural climate variations affect Hawaiian climate. The main analysis concentrates on an important type of natural climate variability in the North Pacific, the Pacific Decadal Oscillation. This research implements dynamical downscaling, that is, a regional climate model is used to refine global climate model simulations in order to better capture the local weather patterns in Hawai'i. We find that land and ocean temperatures across the Hawaiian Islands region will become warmer due to human‐induced causes. We also find that rainfall will likely increase for some areas of Hawai'i, particularly the mountain slopes, posing an increased risk for flooding. The simulations reveal that natural climate variability will continue to contribute to near‐term climate variations in this region. While the natural climate variability limits our confidence in the projected rainfall changes, it is hoped that our findings will assist decision makers across the State of Hawai'i in creating climate adaptation plans. Key Points: Significant increases in near‐surface temperature and sea surface temperature are projected across the Hawaiian Islands regionSignificant increases in mean and extreme rainfall are projected for some areas of the islandsNatural decadal variability will continue to mask the forced signal in near‐term rainfall projections for the Hawaiian Islands [ABSTRACT FROM AUTHOR]

Land‐atmosphere interactions are an essential component of the climate system. However, no detailed description of the underlying effects of the surface forcing of the atmosphere has been established. In this study, GLEAM, MODIS, and ERA5 were the input set of multiple analysis algorithms, "segmentation" was the core idea of the analysis method. The study area is segmented into six surface response functional groups, and the multidimensional evaporation regime function was segmented into piecewise functions controlled by segment authoritative variables. Inspired by the surface heat balance equation and moisture‐limited, energy‐limited evaporation regimes, we chose soil moisture content and the net radiation flux to represent the moisture and energy status, respectively, and chose the leaf area index (LAI) to characterize the vegetation cover to investigate the primary effects of surface parameters on the energy partitioning of the land surface and evaporative regime. The results show that though a coupling strength 1.8 times greater was obtained when the LAI was used as the response variable instead of soil moisture, soil moisture was still the highest response variable in the regression tree analysis. This is consistent with the essence of the evaporative fraction and indicates that water should be the most fundamental response variable. The evaporative regime was subdivided from two phases into five phases according to the effects such as water extraction by vegetation, photosynthesis, soil shading, and roughness changes, each with an authoritative response variable. Key Points: Remote‐sensing data and reanalysis data are the input set of neural network and regression tree, the integrated results of multiple actions are dividedThe study area is segmented into six surface response functional groups, and the evaporation regime is segmented into five piecewise functionsThe coupling strength of leaf area index and evaporative fraction (EF) is 1.8 times greater than that of soil moisture and EF, but soil moisture is still the most preferred variable in the evaporation regime [ABSTRACT FROM AUTHOR]

Based on observational data and numerical simulation results with the Community Atmosphere Model (CAM4), version 4 atmospheric general circulation model (AGCM), the influence of the sea surface temperature anomaly (SSTA) of the tropical Pacific–Indian Ocean mode (PIM) on the interannual variability of the Tibetan Plateau (TP) precipitation in mid‐autumn (October) is investigated. We find that the interannual variation of the mid‐autumn TP precipitation is characterized by a dipole mode with a southeast–northwest inverse pattern, which is influenced significantly by the large‐scale circulation anomalies induced by PIM. During a positive phase of PIM, that is, positive SSTA in both the tropical central‐eastern Pacific and western Indian Ocean accompanied by negative SSTA around the Maritime Continent, a robust lower‐level anticyclonic anomaly over the South Asia region (SAAC) and an upper‐level cyclonic anomaly over subtropical Asia are generated owing to the Rossby wave response to the suppressed convective heating over the northern Maritime Continent. As a result, the southerly (northerly) anomalies on the west (east) side of the SAAC can enhance (reduce) the transportation of moisture and the ascending motion over the northwestern (southeastern) TP. Meanwhile, the southward‐shifted East Asian westerly jet can further enhance the ascending motion over the northwestern TP by stimulating secondary circulation. Correspondingly, a positive (negative) precipitation anomaly appears over the northwestern (southeastern) TP. During a negative phase of PIM, the opposite case is also true. Therefore, the suppressed convective heating over the Maritime Continent serves as a pivotal medium by which PIM affects the TP precipitation in mid‐autumn. Plain Language Summary: The precipitation over the Tibetan Plateau (TP) in mid‐autumn contributes substantially to the atmospheric heating source over the TP in October, which is a triggering factor for the abrupt transition of upper‐atmosphere circulation and the autumn/winter seasonal transition in East Asia. Data diagnosis and numerical simulations show that the tropical Pacific and Indian Ocean temperature anomaly mode (PIM) is a precursor signal for the variation of TP precipitation, characterized by a dipole mode with a southeast‐northwest inverse pattern. The suppressed convection over the northern Maritime Continent is a pivotal medium through which PIM (i.e., positive sea surface temperature anomaly [SSTA] in both the tropical central‐eastern Pacific and western Indian Ocean accompanied by negative SSTA around the Maritime Continent) affects the TP precipitation. It influences the upper‐ and lower‐level atmospheric circulation and provides favorable ascending motion and moisture conditions for the precipitation anomaly over the northwestern TP, while it is out‐of‐phase over the southeastern TP. Therefore, it is necessary to consider the tropical Pacific and Indian Oceans as a unified whole when studying their effects on circulation and precipitation over and around the TP. Key Points: Variation of October precipitation over the TP shows a distinct southeast–northwest inverse patternThe leading SSTA mode across the tropical Pacific and Indian Ocean (PIM) strongly influences the atmospheric circulation over South AsiaThe convection anomaly over the northern Maritime Continent acts as the medium by which PIM affects the TP precipitation [ABSTRACT FROM AUTHOR]

Secondary inorganic ions are important constituents of PM2.5 that play an important role in global climate change through direct and indirect radiative forcing. To investigate the influence of ship emissions on coastal cities, we launched a cruise ship campaign offshore of the East China Sea (ECS) and two field observation sites in the megacity of Shanghai using 1‐hr time‐resolved water‐soluble ion chromatography from June 3 to June 27, 2017. Three main secondary inorganic soluble ions in the atmosphere of the ECS, that is, non‐sea‐salt sulfate (nss‐SO42−), NO3− and NH4+, were 8.87, 4.94, and 4.65 μg m−3, respectively. While their values at the Pudong (PD) station in urban Shanghai were 6.33, 9.47, and 4.74 μg m−3 and at the Dianshanhu (DSH) station in suburban Shanghai were 7.33, 10.01, and 6.78 μg m−3, respectively. Nss‐SO42− was dominant in the PM2.5 in the atmosphere of the ECS (nss‐SO42−/NO3− = 1.8), and mainly distributed near the Zhoushan Islands of the ECS. This indicated significant contributions from ship emissions. Based on the Community Multiscale Air Quality model, two main sources of nss‐SO42− were identified: emissions and horizontal transport. These comprised over 90% of the nss‐SO42−. The influence of ship emissions reached up to 31.6% of the total nss‐SO42− alongside the cruise ship and near coastal parking ports in the Yangtze River Delta area, suggesting that more attention should be paid to ship emissions. Key Points: Non‐sea‐salt sulfate (Nss‐SO42−) was dominant in PM2.5 on East China Sea, which was distributed around Zhoushan Islands indicating a significant contributor of ship emissionTwo main source processing of nss‐SO42− were categorized using Community Multiscale Air Quality: emission and horizontal transportInfluence of ship emission reached up to 31.6% of total nss‐SO42− alongside ship cruise and near coastal parking ports in Yangtze River Delta area [ABSTRACT FROM AUTHOR]

Biomass burning (BB) is a major source of pollutants that impact local, regional, and global climate, air quality, and public health. However, the influence of burning conditions and fuel type on the emission factors of pollutants is still not well understood. Here, we present the results from a laboratory study of emission factors (EFs) of pollutants from six different sub‐Saharan African biomass fuels combusted under a wide range of burning conditions, ranging from smoldering to flaming. We found that particulate matter (PM) and carbon monoxide (CO) EFs (g (kg wood)−1) are highly sensitive to the burning conditions, with an order of magnitude variation between flaming and smoldering burning conditions. Nitric oxide (NO) EF shows a fuel type dependence, with higher NO EFs for fuels with larger nitrogen content. While CO is not generally a proxy for PM2.5 emissions, in this work a correlation was found between CO and PM emissions generated by combustion of seven wood fuels with moisture content (dry basis) <10% in a tube furnace and measured from a laboratory smog chamber with a temperature of ∼21–24°C and an RH below 5%. Unlike total PM, EFs of inorganic particle‐phase species do not show dependence on burning conditions. Finally, we showed that burning biomass fuels in a tube furnace would be a useful experimental approach to study BB emission under controlled burning conditions. Plain Language Summary: Biomass burning is a major source of pollutants that impact climate, air quality, and health. However, the influence of burning conditions and fuel type on the emission factors (EFs) of pollutants is not well understood. An EF relates the quantity of a pollutant released to the atmosphere for a given combustion process and is expressed as grams of emission per kilogram of fuel burned. EFs provide a means to estimate where and how much a pollutant is emitted from various sources so that air quality can be modeled. There are very limited measurements of EFs for African fuels. Here, we present the results from a laboratory study of emission factors of pollutants from six different sub‐Saharan African wooden biomass fuels combusted under a wide range of burning conditions, ranging from smoldering to flaming. We found that the EF of particulate matter and carbon monoxide are sensitive to the burning condition and the EF of nitric oxide depends on the nitrogen content of the fuel. A possible correlation between carbon monoxide emission and particulate matter emission is observed. A tube furnace was used to generate the BB emissions in this work, which offered an opportunity to conduct controlled burning in the laboratory. Key Points: Particulate matter and CO emission factors (EFs) are highly sensitive to the burning conditions of the fuelA correlation was found for CO and PM emissions generated by combustion of wood fuel in a tube furnace and measured in a laboratory chamberFuel nitrogen content plays a significant role in the EF of NO [ABSTRACT FROM AUTHOR]

Historical simulations from twenty‐nine Coupled Model Intercomparison Project Phase 6 (CMIP6) models are used to investigate the consistency among different eddy metrics characterizing the winter North Pacific storm track (WNPST). All CMIP6 models can reproduce the basic climatological characteristics of the WNPST. Results show that, out of the metrics studies, only the upper‐tropospheric filtered meridional wind variance (v′v′) is significantly correlated with the model grid spacing. The climatological amplitudes of different eddy metrics are consistent with each other, except for the consistency between the upper‐tropospheric v′v′ and lower‐tropospheric meridional eddy heat flux and that between the middle‐tropospheric eddy kinetic energy and filtered sea level pressure variance (slp′). The strength trends of different eddy metrics are consistent with each other except for upper‐tropospheric v′v′ and slp′. The meridional migration trends are consistent among different eddy metrics excluding slp′. Given that the sensitivity to horizontal resolution, climatological amplitude, strength trend and meridional migration trend of different Eulerian eddy metrics may exhibit inconsistency, the use of multiple eddy metrics to increase the reliability of the results is suggested. Plain Language Summary: The winter North Pacific storm track, which transports abundant moisture, momentum and heat poleward, is an important component of atmospheric circulation in the Northern Hemisphere and prominently impacts the weather and climate. Based on the Eulerian definition, there are several different band‐pass filtered eddy statistics, including the filtered sea level pressure variance, lower‐tropospheric meridional eddy heat flux, middle‐tropospheric root‐mean‐square filtered geopotential height, eddy kinetic energy and upper‐tropospheric filtered meridional wind variance, commonly used by researchers to characterize storm tracks. However, we do not know whether these different eddy statistics are consistent with each other. Here, we investigate the consistencies among different eddy statistics by using the outputs of twenty‐nine climate models. The results show that there are inconsistencies in the sensitivity to meridional horizontal resolution, climatological amplitude, strength trend and meridional migration trend. If the Eulerian definition is adopted, considering the possible inconsistencies among different eddy statistics, multiple eddy statistics are recommended to increase the reliability of the results. Key Points: The meridional horizontal resolution can only significantly impact the climatological amplitude of v′v′250Inconsistencies occur in the climatological amplitude between v′v′250 and v′t′850 and the strength trend between v′v′250 and slp′If the Eulerian definition is adopted, only using slp′ in climatological variation research or trend analysis should be done carefully [ABSTRACT FROM AUTHOR]

We analyze slow electric field change and lightning mapping measurements to provide insight into the characteristics of volcanic lightning and the associated implications on charging processes and the charge structure of a Vulcanian eruption plume. Data were obtained during a multi‐instrumental field campaign at Sakurajima volcano in 2015 when the Showa crater was active. We combine the electric field change and lightning mapping data from one explosive eruption on June 6, 2015 to identify individual flashes. From this, we interpret the flash type and polarity. In addition, the long‐time constant of the electric field change instrument allowed measurement of the quasi‐static field associated with charge separation in the eruption plume. We find that both intracloud and cloud‐to‐ground discharges occurred, and the polarity of cloud‐to‐ground discharges were all negative. The quasi‐static field measurement showed the plume carried a net negative charge. We calculate both the total charge transferred by cloud‐to‐ground discharges and the net charge density of the eruption plume. We find that cloud‐to‐ground discharges transfer an average of −0.41C per flash and the net charge density was −33C/km3. The percent error is at least 200%, due to uncertainty in the antenna gain. We show that these estimates are consistent with lightning that is 100 m in length. Further, the average flash rate during the first 8 s following the onset of eruption was five flashes per second. After that time, the flash rate abruptly decreased, which may be related to the end of gas‐thrust forcing. Key Points: Vulcanian eruption plumes have a charge density of up to two orders of magnitude greater than thunderstormsThe abrupt decrease in flash rates several seconds after the onset of the explosion may be linked to the cessation of gas‐thrust forcingThe polarity of cloud‐to‐ground flashes were negative, but evidence exists that other explosive events produce positive polarity CGs [ABSTRACT FROM AUTHOR]

Using the geopotential height measurements from the Aura Microwave Limb Sounder and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere‐Ionosphere‐Mesosphere Energetics and Dynamics satellite, we found eight westward quasi‐8‐day wave (Q8DW) events with zonal wavenumber 1 (W1) during the Arctic sudden stratospheric warmings (SSWs) in 2005–2020. The W1 Q8DW perturbations are mainly confined to the middle and high latitudes in the Northern Hemisphere, and peak at ∼50–80 km. Specified Dynamics Whole Atmosphere Community Climate Model eXtended version simulations are utilized to reproduce the Q8DW activities. The diagnostic results indicate that the W1 Q8DWs originate from the high latitudes in the Northern Hemisphere stratosphere. Their excitation, propagation, and amplification are primarily influenced by the critical layers and baroclinic/barotropic instability, which are dependent on the background conditions during SSWs. Our statistical results show that the W1 planetary waves with periods shorter than 12 days during the Arctic SSWs are most frequently observed at the period of ∼8 days, which is significantly different from the climatological periods of the Rossby (1, 1) and (1, 2) normal modes (6.14 and 9.81 days, respectively). These results indicate that the W1 Q8DW may be a new wave mode. Finally, we found that the reversal (or deceleration) and the recovery of the zonal mean flow during SSWs can result in a zonally symmetric Q8DW, and the W1 Q8DW is likely the child wave generated by the nonlinear interaction between the stationary planetary wave with zonal wavenumber 1 and zonally symmetric Q8DW. Key Points: The westward quasi‐8‐day wave (Q8DW) with zonal wavenumber 1 (W1) is observed eight times during the Arctic sudden stratospheric warmings (SSWs) from 2005 to 2020The SD‐WACCM‐X simulation results show that the Q8DW activities during SSWs are highly influenced by the critical layers and instabilitiesThe W1 Q8DWs during the Arctic SSWs are most likely generated from the zonally symmetric wave‐stationary wave nonlinear interactions [ABSTRACT FROM AUTHOR]

This study characterizes the representation of convective transport by a Lagrangian trajectory model driven by kinematic (pressure tendency ω) vertical velocity. Four (re)analysis wind products are used in backward trajectory calculations with the TRAJ3D model, and their representations of convective transport are analyzed. Two observation‐based diagnostics are used for the evaluation: a database of observed convective cloud tops derived from satellite measurements and a set of transit time distributions (TTDs) derived from an airborne campaign during January–February 2014 in a domain over the Tropical Western Pacific (TWP). The analysis is designed to derive trajectory‐based TTDs that can be directly evaluated using the observation‐based TTDs. The results indicate a broad consistency between two independent TTD derivations characterizing vertical transport over the TWP, with a significant portion of convective transport processes represented in trajectory experiments driven by the selected (re)analysis wind products. The convective and boundary layer source regions of upper tropospheric air parcels are shown to be consistent with the climatological flow regime within the TWP. Furthermore, contributions of convection are identified in the ω fields of the (re)analysis wind data sets, as indicated by the spatiotemporal correlation of enhanced vertical velocity and observed convection. These results demonstrate the successful application of two observation‐based diagnostics and quantify the ability for kinematic trajectory models to represent convective transport processes. Key Points: Two observation‐based diagnostics are used to characterize the representation of convective transport in Lagrangian trajectory modelsTransit time distributions calculated by kinematic trajectory models capture a significant portion of convective transport processesSpatiotemporal colocation of enhanced kinematic vertical velocity with observed convection is found in chosen (re)analysis data sets [ABSTRACT FROM AUTHOR]