Search

Mercury (Hg) is a global pollutant with substantial risks to human and ecosystem health. By upward transport in tropical regions, mercury enters into the stratosphere, but the contribution of the stratosphere to global mercury dispersion and deposition remains unknown. We find that between 5 and 50% (passing through the 400-kelvin isentropic surface and tropopause, respectively) of the mercury mass deposited on Earth's surface is chemically processed in the lower stratosphere. Our results show the stratosphere as a unique chemical environment where elemental mercury is efficiently converted to long-lived oxidized species. Subsequent downward transport contributes substantially to the oxidized mercury burden in the troposphere. The results show that the stratosphere facilitates the global dispersion of large amounts of mercury from polluted source regions to Earth's remote environments. We find that stratospheric transport is as important as tropospheric transport in interhemispheric mercury dispersion. Future projections suggest that expected changes in atmospheric circulation will increase the transport of mercury into the stratosphere. [ABSTRACT FROM AUTHOR]

Improvement of subseasonal to seasonal North Atlantic winter forecasting requires better prediction of the North Atlantic Oscillation (NAO), the dominant mode of variability in the Northern Hemisphere. Despite recent research demonstrating the importance of stratosphere‐troposphere coupling for NAO predictability, the driving mechanisms and implications are not fully understood. This study reveals that the October upper stratosphere is highly relevant to polar vortex development and predictability of winter NAO. We derive a simple index based on the strength of meridional wind in the upper stratospheric surf zone and find that anomalously poleward motion is associated with a significantly stronger polar vortex, which predicts the subsequent winter surface NAO with a correlation coefficient of r = 0.40. Plain Language Summary: The North Atlantic Oscillation (NAO) is a large‐scale atmospheric system that significantly affects the weather and climate in the North Atlantic basin, especially in winter. Accurately forecasting the NAO 1–3 months ahead is challenging. However, on these timescales, more predictable factors like the stratosphere play a crucial role in modulating the NAO. The upper stratosphere plays a significant role in stratospheric dynamics, however it remains poorly understood and its potential to improve winter NAO predictions is largely untapped. Here, we create a simple index to measure the north‐south winds in the upper stratosphere during October and find that a positive index predicts a stronger winter polar vortex, leading to a more positive NAO. This results in warmer, wetter, and stormier conditions in northern Europe and the eastern US, and colder, drier conditions in southern Europe and Canada. Conversely, a negative index indicates a weaker winter polar vortex and an increased likelihood of sudden stratospheric warming events, which can often lead to extreme and prolonged cold conditions at the surface. Our findings highlight the importance of monitoring the upper stratosphere in October to improve winter NAO predictions and better understand stratosphere‐troposphere coupling. Key Points: The meridional wind in the midlatitude upper stratosphere in October contains significant seasonal predictability for the winter NAOThe strength of the meridional wind in this region also predicts changes in the occurrence of midwinter SSWsThe winter surface impact of the October upper stratospheric wind occurs partly, but not entirely, via changes to the polar vortex [ABSTRACT FROM AUTHOR]

The minor sudden stratospheric warming (SSW) event and the relevant planetary waves are investigated by analyzing ERA5 reanalysis data from July to December 2019. Frequency-wavenumber spectral analysis shows that the quasi-10-day and quasi-16-day waves dominate the stratosphere over the Southern Hemispheric polar region with the eastward-propagating wavenumber 1 during the SSW event. The corresponding amplitudes and phases of each wave mode have been fitted using the two-dimensional harmonic fitting method. The result suggests that quasi-16-day and quasi-10-day waves prior to the SSW event had an important effect on the occurrence of the SSW event. Furthermore, the Eliassen–Palm flux diagnosis shows that the quasi-16-day wave and quasi-10-day wave had poleward and equatorward-propagating components. The poleward-propagating component may have come from the tropical tropospheric convective activity. The equatorward component may have been excited by the atmospheric barotropic/baroclinic instability. [ABSTRACT FROM AUTHOR]

Mixed Rossby‐gravity (MRG) waves play a significant role in tropical variability. Their kinetic energy spectra exhibit maximal amplitudes at synoptic scales in the upper troposphere and at planetary scales in the upper stratosphere. The mechanism for different scale selection in the two regions has remained elusive. Here, we use a spherical barotropic model with the background zonal wind profiles derived from ERA5 reanalysis to show that the recently introduced MRG wave excitation mechanism − ${-}$ wave‐mean flow interactions produces MRG waves with the observed scale properties in the two regions. Simulations with idealized zonal jets show that the jet position determines the MRG scale selection: the closer the jet to the equator, the smaller the scale of the excited MRG waves. Therefore, midlatitude jets, such as found in the upper stratosphere, support the excitation of planetary‐scale MRG waves. Plain Language Summary: Mixed Rossby‐gravity (MRG) waves, which are important for tropical weather and climate, obtain different spatial scales in two distinct atmospheric regions: synoptic scales in the upper troposphere and planetary scales in the upper stratosphere. So far, the mechanism responsible for this behavior is not identified. In this study, we propose interactions involving waves that originate from the tropics and zonal jets (i.e., wave‐mean flow interactions) as the mechanism behind the observed MRG wave scales. We provide evidence by conducting numerical simulations with an idealized model that resolves MRG waves with high accuracy. We identify MRG waves generated by wave‐mean flow interactions and show that their peak scale can be attributed to the position of the jet. The closer the jet to the equator, the smaller the scale of generated MRG waves. This not only offers an explanation for the observed spatial scales of the tropospheric and stratospheric MRG waves, but also points out the importance of the background flow to correctly represent MRG waves in weather and climate models. Key Points: Mixed Rossby‐gravity waves in the upper stratosphere and troposphere have peak scales at zonal wavenumbers 1–3, and 6, respectivelyObserved peak scales are generated by wave‐mean flow interactions in numerical simulations with the observed zonal‐mean zonal wind profilesThe peak MRG scale is associated with the jet position: the closer the jet to the equator, the smaller the scale of the excited waves [ABSTRACT FROM AUTHOR]

The Brewer‐Dobson circulation (BDC) characterizes the large‐scale meridional overturning mass circulation influencing the composition of the whole middle atmosphere. The BDC consists of two separate parts—a shallow branch in the lower stratosphere and a deep branch higher in the middle atmosphere. Climate models robustly project the advective BDC part to accelerate due to greenhouse gas‐induced climate change and this acceleration strongly influences middle atmospheric chemistry and physics in the projections. A prominent quantity that is being studied as a proxy for advective BDC changes is the net tropical upwelling across pressure levels, particularly in the lower stratosphere. The upper branch of the BDC has received considerably less research attention than its shallow part, although, together with the mean mesospheric pole‐to‐pole circulation, it couples the stratosphere and mesosphere and is responsible for a large portion of the interhemispheric transport in the middle atmosphere. Aiming to fill this gap, we here study climatology and trends in advective mass transport across the stratopause. Results based on the analysis of seven CCMI models include quantification of the climatological cross‐stratopause advective transport, characterization of its interannual variability and long‐term trend as well as detailed analysis of inter‐model differences using a novel decomposition methodology. Our results demonstrate that the changes in circulation speed as well as changes in horizontal and vertical structure in the upper stratosphere and mesosphere jointly shape the projected increasing advective mass flux across the stratopause due to increasing greenhouse‐gas emissions. Plain Language Summary: The Brewer‐Dobson circulation (BDC) is an important circulation pattern, affecting the composition of the entire middle atmosphere. Our study focuses on the less‐studied higher part of the BDC, which connects the stratosphere and mesosphere. Analyzing comprehensive climate model simulations, we found changes in circulation speed, along with horizontal and vertical structure changes of the upper BDC branch as a response to increasing greenhouse gas emissions. Understanding these changes aids improvements of climate predictions and highlights the significant influence of human activities on the atmosphere. Key Points: Advective transport between the stratosphere and mesosphere exhibits a robust annual cycleModels project an average amplification of cross‐stratopause transport of about 1% per decade during all seasonsThe transport decomposition reveals inconsistencies between the models regarding the causes of long‐term changes [ABSTRACT FROM AUTHOR]

During austral winter, the southern high latitudes has some of the most intense stratospheric gravity wave (GW) activity globally. However, producing accurate representations of GW dynamics in this region in numerical models has proved exceptionally challenging. One reason for this is that questions remain regarding the relative contributions of orographic and non‐orographic sources of GWs here. We use three‐dimensional (3‐D) satellite GW observations from the Atmospheric Infrared Sounder in austral winter 2012 in combination with the Gravity‐wave Regional Or Global Ray Tracer to backward trace GW rays to their sources. We trace over 14.2 million rays, through ERA5 reanalysis background atmosphere, to their lower atmospheric sources. We find that GWs observed thousands of km downstream can be traced back to key orographic regions, and that on average, all waves (orographic and non‐orographic) converge meridionally over the Southern Ocean. We estimate that across this winter, orographic sources contribute around ∼ ${\sim} $ 5%–35% to the total momentum flux (MF) observed near 60° ${}^{\circ}$S. The remaining proportion consists of waves from non‐orographic sources, which although typically carry lower MF, the large spatial extent of non‐orographic sources leads to a higher overall contribution. We also quantify the proportion of MF traced back to different regions across the whole southern high latitudes area in order to measure the relative importance of these different regions. These results provide the important insights needed to advance our knowledge of the atmospheric momentum budget in the southern high latitudes. Plain Language Summary: Just like the ocean, our atmosphere contains waves which transport energy and momentum. These atmospheric waves, known as gravity waves (GWs), strongly influence large‐scale wind patterns but are hard to represent in climate models. The Southern Hemispheric stratosphere has some of the strongest GW activity on our planet and accurately representing this region in models has proved exceptionally challenging. Further, inaccurate representations of gravity waves can lead to major model biases. Here, we use satellite observations of stratospheric GWs and, using new methods, identify GWs and measure GW amplitudes, wavelengths, and directions. We then use these observations in combination with a ray‐tracing model to track observed GWs back to their sources near the ground. This approach means that, for the first time, we are able to produce systematic estimates of the relative contribution of different wave sources to the observed stratospheric activity in the southern high latitudes. Key Points: We use gravity wave properties derived from stratospheric satellite observations as input to a backward ray‐tracing modelRay‐tracing reveals that gravity waves observed at all longitudes around the Southern Ocean converge to 60°S as they propagate upwardWe quantify the momentum flux (MF) from different regions, finding that, in winter 2012, over half of the MF is traced back to the ocean [ABSTRACT FROM AUTHOR]

Volcanic Ash Advisory Centers (VAACs) have generated volcanic ash forecasts for the aviation industry since the mid‐1990s. The excellent spatial and temporal coverage of satellite data makes them critical to the validation of ash dispersion model forecasts. This study investigates the limitations of satellite‐retrieved volcanic ash data through the production of simulated radiances for a range of ash cloud properties encompassing the satellite retrieval's sensitivity. We run a detection and retrieval algorithm (Francis et al., 2012, https://doi.org/10.1029/2011JD016788) on these simulated ash clouds and assess the sensitivity and performance of the algorithms. Expected limitations are highlighted, including a lack of sensitivity to particles larger than ∼10 μm in radius and challenges in accurately retrieving heights in the stratosphere. However, other previously poorly defined limitations are also constrained, such as the reduction in sensitivity as ash column loading increases in optically thick ash clouds and increasingly underestimated column loading when column loadings are >∼7 g m−2. We consider the implications of the identified limitations when using satellite‐retrieved ash column loadings to verify dispersion model output. We show that, accounting for the limitations of the satellite retrieval, a significant proportion of mass in the model output can lie outside the sensitivity range of the satellite detection and retrieval. This demonstrates the importance of understanding observations' limitations when comparing to model output. This knowledge should be used when verifying operational volcanic ash cloud forecasts. Plain Language Summary: Volcanic Ash Advisory Centers (VAACs) were created to forecast the location of airborne volcanic ash as it is a hazard to aircraft. These forecasts are produced by dispersion models, which combine estimates of the ash ejected by the volcano with meteorological information to forecast the location and amount of ash in the atmosphere. Observations, particularly satellite data, are required to validate the forecasts. However, satellite data also has uncertainty and this can vary significantly for different ash clouds. This paper investigates the uncertainty in quantitative satellite data, constraining previously poorly defined biases, such as limitations for larger ash particles and regions where large amounts of ash are present. These limitations are then considered when comparing quantitative satellite data to quantitative dispersion model output. This showed that significant portions of ash mass present in dispersion model output may be outside the quantitative satellite data's sensitivity range. This has important implications for the use of quantitative satellite volcanic ash data to validate dispersion model output. Key Points: A volcanic ash retrieval was run on simulated radiances produced for a large range of ash cloud propertiesThis constrained limitations on the detection and retrieval's performance at different ash column loadings, heights, and particle sizesSignificant portions of ash mass present in dispersion model output were shown to be outside the satellite retrieval sensitivity range [ABSTRACT FROM AUTHOR]

This work is devoted to the study of the upper stratosphere circulation features in quiet and disturbed periods. A comparative analysis of blocking properties of the polar stratospheric vortex during December and January 2019–2021 is carried out. ERA5 reanalysis data and Aura-MLS satellite data are used. To determine the inner boundary of the polar vortex, the method of launching test particles in a three-dimensional field of wind speed values is used, forcing the particles to form closed circulation structures. The focus of this work is to determine the differences in the dynamics of the stratospheric vortex under quiet and disturbed conditions. It is shown that, during the development of the main phase of a sudden stratospheric warming similar to the one that occurred in January 2021, the circulation structure of the vortex is destroyed. This vortex disruption contributes to significant "meridional" mixing of the polar stratosphere. Estimates of average vertical velocity of movement of the test particles are made. [ABSTRACT FROM AUTHOR]

Age of stratospheric air is a well established metric for the stratospheric transport circulation. Rooted in a robust theoretical framework, this approach offers the benefit of being deducible from observations of trace gases. Given potential climate‐induced changes, observational constraints on stratospheric circulation are crucial. In the past two decades, scientific progress has been made in three main areas: (a) Enhanced process understanding and the development of process diagnostics led to better quantification of individual transport processes from observations and to a better understanding of model deficits. (b) The global age of air climatology is now well constrained by observations thanks to improved quality and quantity of data, including global satellite data, and through improved and consistent age calculation methods. (c) It is well established and understood that global models predict a decrease in age, that is, an accelerating stratospheric circulation, in response to forcing by greenhouse gases and ozone depleting substances. Observational records now confirm long‐term forced trends in mean age in the lower stratosphere. However, in the mid‐stratosphere, uncertainties in observational records are too large to confirm or disprove the model predictions. Continuous monitoring of stratospheric trace gases and further improved methods to derive age from those tracers will be crucial to better constrain variability and long‐term trends from observations. Future work on mean age as a metric for stratospheric transport will be important due to its potential to enhance the understanding of stratospheric composition changes, address climate model biases, and assess the impacts of proposed climate geoengineering methods. Plain Language Summary: Transport strongly influences the composition of the stratosphere, the layer at around 10–50 km altitude. Air masses are transported upward into the stratosphere in the tropics, and get distributed globally by a hemisphere‐wide overturning circulation. Stratospheric age of air is a measure of the transport times along this circulation. This metric is a crucial measure of the circulation strength, deducible from observations of certain stratospheric gases. Over the past two decades, scientific progress has been made in three main areas. First, we now understand better which processes influence transport times. Second, we have good knowledge on the global average distribution of age of air, thanks to more observational data and improved methods to deduce this metric. Third, a large focus has been on climate‐change related trends in age of air. While it is well established and understood that global models predict an accelerating stratospheric circulation, the related decrease in age of air can only be confirmed observationally in the lower stratosphere. Continuous monitoring of stratospheric trace gases will be crucial to constrain circulation trends throughout the stratosphere. This is essential for understanding climate change effects, improving climate models, and assessing potential climate intervention strategies. Key Points: Understanding of how individual processes impact stratospheric age of air has been improved through development of dedicated diagnosticsThe global age of air climatology is now well constrained by observations thanks to improved data records and age calculation methodsObserved age trends confirm lower stratospheric model predictions but are too uncertain to confirm or dismiss middle stratospheric trends [ABSTRACT FROM AUTHOR]

Two decades of ACE-FTS, the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer, version 5.2 (v5.2) ozone data (2004–2023) are evaluated with ozonesonde data from across the globe. The biases between the ACE-FTS and ozonesonde measurements are first estimated by analyzing coincident data pairs. A second approach is taken for the validation by comparing the ACE-FTS and ozonesonde monthly mean time series, with the former generated by sampling the ACE-FTS data within latitude/longitude boxes (i.e., ± 5°/ ± 30°) surrounding the stations and calculating the monthly averages. The biases, correlations, variation patterns, and the mean states of the two time series are compared. The biases estimated in this way exhibit more consistent and smoother features than using the coincident pair method. The ACE-FTS and ozonesonde monthly mean time series are highly correlated and exhibit similar variation patterns in the lower stratosphere at all latitudes. The ACE-FTS instrument drifts for each station are assessed in terms of the long-term linear trends relative to ozonesondes, which, although highly stable, may have their own minor changes with time. The ACE-FTS ozone profiles exhibit in general high biases in the stratosphere for altitudes above ∼ 20 km, increasing with altitude up to ∼ 10 % at around 30 km. For altitudes between 20 km and the tropopause, biases of up to ± 10 % are found, depending on altitude and latitude with the largest biases found in the tropics and southern mid-latitudes. The ACE-FTS instrument drifts are generally non-significant overall in the stratosphere with high variation between the stations. Averaging the individual station instrument drifts within several latitude bands results in small non-significant drifts of within ± 1 %–2 % per decade in the northern mid-latitudes to high latitudes and the southern high latitudes. It also results in a positive but non-significant drift of up to 5 % per decade in the tropics and southern mid-latitudes, with overall uncertainties in this region ranging up to 5 %–10 % per decade (2 σ level) in the low stratosphere. As part of this assessment, an analysis of ozonesonde measurement stability using ACE-FTS as a transfer standard is conducted and finds small step changes in ozonesonde response at some stations. These results are in general agreement with recent findings using other satellite data sources. [ABSTRACT FROM AUTHOR]

Observations of the Jovian upper atmosphere at high latitudes in the UV, IR and mm/sub-mm all indicate that the chemical distributions and thermal structure are broadly influenced by auroral particle precipitations. Mid-IR and UV observations have shown that several light hydrocarbons (up to 6 carbon atoms) have altered abundances near Jupiter's main auroral ovals. Ion-neutral reactions influence the hydrocarbon chemistry, with light hydrocarbons produced in the upper stratosphere, and heavier hydrocarbons as well as aerosols produced in the lower stratosphere. One consequence of the magnetosphere-ionosphere coupling is the existence of ionospheric jets that propagate into the neutral middle stratosphere, likely acting as a dynamical barrier to the aurora-produced species. As the ionospheric jets and the background atmosphere do not co-rotate at the same rate, this creates a complex system where chemistry and dynamics are intertwined. The ion-neutral reactions produce species with a spatial distribution following the SIII longitude system in the upper stratosphere. As these species sediment down to the lower stratosphere, and because of the progressive dynamical decoupling between the ionospheric flows and the background atmosphere, the spatial distribution of the auroral-related species progressively follows a zonal distribution with increasing pressures that ultimately produces a system of polar and subpolar hazes that extends down to the bottom of the stratosphere. This paper reviews the most recent work addressing different aspects of this environment. [ABSTRACT FROM AUTHOR]

The dynamical tropopause acts as a transport barrier between the tropical upper troposphere and extratropical lowermost stratosphere and is characterized by steep gradients in potential vorticity (PV) along an isentropic surface. Hence, the latitudinal separation between the dynamical tropopause in the Northern Hemisphere and Southern Hemisphere can be used as a metric of upper-tropospheric width for assessing climate change impacts. Here, we obtain the PV-gradient-based dynamical tropopause (PVG tropopause) from four meteorological satellite-era reanalyses (ERA5, ERA-Interim, JRA-55, MERRA-2) and investigate its climatology, variability and long-term trends from 1980 to 2017. Our results show a distinct seasonal cycle with larger PV values and a poleward movement of the PVG tropopause in summer. The climatological tropopause PV values are substantially different between different reanalyses, but the tropopause latitude is similar. Significant interannual variability in the PVG tropopause latitude is related to the El Niño–Southern Oscillation (ENSO) and weaker variability also to the quasi-biennial oscillation (QBO) and is consistently represented in reanalyses. In particular, El Niño correlates with equatorward shifts in the PVG tropopause and hence a decrease in upper-tropospheric width. Long-term trends in the PVG tropopause over the period 1980–2017 exhibit a distinct vertical structure with poleward shifts below 340 K potential temperature, equatorward shifts between 340 and 370 K , and poleward shifts between 370 and 380 K. This consistent widening at lower levels and narrowing in the upper troposphere also exhibit considerable zonal variability with the strongest upper-tropospheric narrowing over the eastern Pacific. [ABSTRACT FROM AUTHOR]

A quasi-biennial oscillation (QBO) disruption is a very rare phenomenon in which QBO westward wind is temporarily interrupted by the occurrence of a band of westward wind in the tropical stratosphere. This phenomenon is important as it could greatly affect the global atmospheric circulation, especially in the mesosphere. Past observational and modelling studies have shown the QBO varying mesospheric diurnal tide, but the mechanism is still not fully understood. In this study, we report on the strong response of mesospheric diurnal tides to the two QBO disruptions that occurred in 2015–2016 and 2019–2020 and their possible mechanisms. The diurnal tidal winds are observed by a meteor radar chain, consisting of meteor radars located at Kunming (25.6° N, 103.8° E), Wuhan (30.5° N, 114.2° E), Mengcheng (33.4° N, 116.5° E), Beijing (40.3° N, 116.2° E), and Mohe (53.5° N, 122.3° E) in China. These observations provide clear evidence that mesospheric diurnal tides are unusually weakened (by ∼ -6 m s−1) during these QBO disruptions, over Kunming, Wuhan, Mengcheng, and Beijing. Using the Specific Dynamics version of the Whole Atmosphere Community Climate Model with thermosphere and ionosphere extension (SD-WACCM-X) and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis v5 (ERA5) dataset, the analysis indicates that the QBO wind affects mid-latitude mesospheric diurnal tides by modulating both the solar radiative absorption by subtropical stratospheric ozone (∼ 5 to 0.5 hPa) and the tidal–gravity wave interaction in the mesosphere (∼ 60 to 100 km). Thus, these unexpected QBO disruptions provide an opportunity to better understand the coupling between climate change and middle-atmospheric dynamics. [ABSTRACT FROM AUTHOR]

Stratospheric aerosol injection (SAI) refers to a climate intervention method by which aerosols are intentionally added to the lower stratosphere to enhance sunlight reflection and offset some of the adverse effects of global warming. The climate outcomes of SAI depend on the location, amount, and timing of injection, as well as the material used. Here, we isolate the role of the latitude of SO2 injection by comparing different scenarios that have the same global-mean temperature target, altitude of injection, and hemispherically symmetric injection rates. These are as follows: injection at the Equator (EQ) and injection at 15° N and S (15N + 15S), 30° N and S (30N + 30S), or 60° N and S (60N + 60S). We show that injection at the Equator leads to a substantial undercooling of the Arctic, a significant reduction in tropical precipitation, reductions in high-latitude ozone, heating in the tropical lower-stratosphere, and strengthening of the stratospheric jets in both hemispheres. Additionally, we find that the most efficient injection locations are the subtropics (15 and 30° N and S), although the 60N + 60S strategy only requires around 30 % more SO2 injection for the same amount of cooling; the latter also leads to much less stratospheric warming but only marginally increases high-latitude surface cooling. Finally, while all the SAI strategies come with trade-offs, our work shows that the 30N + 30S strategy is a good candidate strategy for an intermodel comparison and is easier to implement than a multi-latitude controller algorithm. [ABSTRACT FROM AUTHOR]

During the summer season, deep convection over the central United States has a significant impact on the dynamics and composition of the upper troposphere and lower stratosphere (UTLS). These storms transport tropospheric air containing trace gases, ice particles, and aerosols into the UTLS, which can affect chemical and radiative processes over a large region. Because overshooting storms necessarily have strong updrafts, there is a marked correlation between overshooting and the occurrence of severe weather at the surface. Heat released by these storms also helps to drive the North American Monsoon Anticyclone (NAMA) in the UTLS, which partially confines air injected into the stratosphere by overshooting storms. In support of the Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) project, this study is a climatological analysis of the environmental factors that affect the occurrence of deep and overshooting storms. Using hourly analyses of overshooting storms based on GridRad radar data and ERA5 reanalyzes, we focus on the roles of convective available potential energy (CAPE), convective inhibition (CIN), jet location, and other relevant dynamical and thermodynamic variables. The results show that northward intrusion of airmasses containing moist high CAPE air from the Gulf of Mexico into the central plains plays a major role in producing the conditions necessary for overshooting storms with other factors playing secondary roles. Plain Language Summary: Using observations of the atmosphere, this research shows that strong convective storms, which are most likely to produce heavy rain and severe weather, are regulated primarily by the amount of energy available to drive the storms and the energy needed to initiate convection. The strongest storms can also penetrate into the overlying stratosphere, which contains the Earth's protective ozone layer, carrying air from the lower atmosphere into the stratosphere. This is significant in part because climate models predict that the amount of energy available for convection will increase as the climate warms. As a result, the impact of strong convection on the atmosphere and on the stratosphere in particular may increase over coming decades. Key Points: Overshooting convective storms have a global impact on the composition, chemistry, and radiative balance of the overlying stratosphereDeep and overshooting storms are strongly correlated with convective available potential energy (CAPE) and convective inhibition (CIN)CAPE and CIN are predicted to increase as the climate warms, potentially increasing the impact of overshooting storms on the stratosphere [ABSTRACT FROM AUTHOR]

Global average upper atmosphere temperature changes linked with the Hunga volcanic eruption (January 2022) are analyzed based on satellite measurements and compared with chemistry‐climate model simulations. Results show stratospheric cooling of −0.5 to −1.0 K in the middle and upper stratosphere during 2022 through middle 2023, followed by stronger cooling (−1.0 to −2.0 K) in the mesosphere after middle 2023. The cooling patterns follow the upward propagating water vapor (H2O) anomalies from Hunga, and similar behavior is found between observations and model simulations. While the stratospheric cooling is mainly due to radiative cooling from enhanced H2O, the mesospheric temperature changes result from ozone losses in the mesosphere, which are in‐turn driven by HOx radicals from Hunga H2O. Comparisons with the multi‐decade climate record show that Hunga impacts on stratospheric temperatures have similar magnitude, but opposite sign, to temperature effects from the large El Chichón (1982) and Pinatubo (1991) volcanic eruptions. Plain Language Summary: We analyze temperature changes in the upper atmosphere due to the Hunga volcanic eruption in January 2022 using satellite observations and simulations from a state‐of‐the‐art chemistry‐climate model. Hunga was an underwater volcano that emitted a large amount of water vapor (H2O) directly into the stratosphere, and this H2O has moved slowly upwards over time and mostly remains in the upper atmosphere. Observations show cooling of the stratosphere (20–50 km) by 0.5–1.0 K during 2022 to middle 2023, and cooling of the mesosphere (50–80 km) by 1.0–2.0 K after middle 2023. The cooling patterns follow the upward moving Hunga H2O plume. The model simulations show good agreement with observations, and the model is used to diagnose that the cooling is due to Hunga H2O impacts. The long‐lasting, global‐scale cooling from Hunga has similar magnitude, but opposite sign, to stratospheric warming observed from previous large volcanic eruptions (El Chichón in 1982 and Pinatubo in 1991); the differences are due to the large H2O emitted by Hunga. Key Points: Global average cooling of 1–2 K is observed in the upper atmosphere during 2022–2024 following Hunga eruption in January 2022Good agreement of observations with chemistry‐climate model simulations; cooling is mainly due to Hunga H2O impactsHunga‐forced cooling is comparable in magnitude to stratospheric warming following El Chichón (1982) and Pinatubo (1991) eruptions [ABSTRACT FROM AUTHOR]

Stratospheric transit time distributions (age‐of‐air spectra) are estimated using time series of satellite water vapor (H2O) measurements from the Microwave Limb Sounder over 2004 to 2021 assuming stationary transport. Latitude‐altitude dependent spectra are derived from correlations of interannual H2O anomalies with respect to the tropical tropopause source region, fitted with an inverse Gaussian distribution function. The reconstructions accurately capture interannual H2O variability in the "tropical pipe" and near‐global lower stratosphere, regions of relatively fast transport (∼1–2 years) in the Brewer‐Dobson circulation. The calculations provide novel observational estimates of the corresponding "short transit‐time" part of the age spectrum in these regions, including the mode. However, the H2O results do not constrain the longer transit‐time "tail" of the age spectra, and the mean age of air and spectral widths are systematically underestimated compared to other data. We compare observational results with parallel calculations applied to the WACCM chemistry‐climate model and the CLaMS chemistry‐transport model, and additionally evaluate the method in CLaMS by comparing with spectra from idealized pulse tracers. Because the age spectra accurately capture H2O interannual variations originating from the tropical tropopause, they can be used to identify "other" sources of variability in the lower stratosphere, and we use these calculations to quantify H2O anomalies in the Southern Hemisphere linked to the Australian New Years fires in early 2020 and the Hunga volcanic eruption in 2022. Plain Language Summary: Stratospheric water vapor (H2O) is mainly controlled by transport across the cold tropical tropopause, which sets the entry value for the global stratosphere. Interannual variations in H2O originate near the tropical tropopause and then propagate throughout the stratosphere with the global Brewer‐Dobson circulation (BDC), where anomalies are lagged in time and smoothed by mixing. We use the observed time series of H2O from the Microwave Limb Sounder during 2004–2021 to calculate transit time distributions (also called age spectra) from the tropical tropopause source region. The results capture H2O variability in the tropics up to 30 km and in the global lower stratosphere, regions of relatively fast transport (∼1–2 years) in the BDC. The calculations provide novel observational estimates of the age spectra in these regions. The calculations are straightforward to apply to global models, and we compare observational results with simulations from the WACCM and CLaMS models. Key Points: Stratospheric transit time distributions (age spectra) are derived from time series of satellite water vapor measurementsWater vapor reconstructions from age spectra capture detailed variability in the tropics up to 30 km and in the global lower stratosphereAge spectrum results are compared between observations and global model simulations [ABSTRACT FROM AUTHOR]

Temperature trends in the upper stratosphere, particularly above ∼ 45 km, are difficult to quantify due to a lack of observational data with high vertical resolution in this region that span multiple decades. The recent v7.3 upper-stratospheric (35–60 km) temperature data product from the Optical Spectrograph and InfraRed Imager System (OSIRIS) includes over 22 years of observations that can be used to estimate temperature trends. The trends in OSIRIS temperatures over 2005–2021 are compared to those from two other satellite limb instruments: Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) and Microwave Limb Sounder (MLS). We find that the upper stratosphere cooled by ∼ 0.5 to 1 K per decade during this period. Results from the three instruments are generally in agreement. By merging the OSIRIS observations with those from channel 3 of the Stratospheric Sounding Unit (SSU), we find that the stratosphere cooled at a rate of approximately - 0.6 K per decade between 1979 and 2021 near 45 km, in agreement with earlier results based on SSU and MLS. The similarity between OSIRIS temperature trends and those from other records improves confidence in observed upper-stratospheric temperature changes over the last several decades. [ABSTRACT FROM AUTHOR]

Simultaneous observations using a long-duration balloon and the PANSY radar, a large-scale atmospheric radar, were performed at Syowa Station in the Antarctic, from January to February 2022. They captured near-inertial frequency gravity waves (NIGWs) in the lower stratosphere. The analysis using both datasets and the latest reanalysis ERA5 revealed that two NIGW packets with an upward group velocity and short vertical wavelengths of less than 3 km propagated northeastward and eastward above Syowa Station. Although the NIGWs over Syowa Station were qualitatively represented by ERA5, their amplitudes were underestimated. In addition, the latter NIGW packet was observed by the long-duration balloon, but not represented by ERA5. It could be because the vertical wavelength of NIGW became shorter than the lower limit of vertical wavelength explicitly represented in ERA5 by entering the high static stability region around the balloon, or due to explicit and implicit diffusion and/or misrepresentation of the position of the NIGW packet in the model. This result implies the difficulty to explicitly represent the behavior of NIGWs with short vertical wavelengths even in the high-resolution simulation. [ABSTRACT FROM AUTHOR]

An array of SuperDARN meteor radars at northern high latitudes was used to investigate the sources and characteristics of eastward-propagating planetary waves (EPWs) at 95 km, with a focus on wintertime. The nine radars provided the daily mean meridional winds and their anomalies over 180 degrees of longitude, and these anomalies were separated into eastward and westward waves using a fast Fourier transform (FFT) method to extract the planetary wave components of zonal wavenumbers 1 and 2. Years when a sudden stratospheric warming event with an elevated stratopause (ES-SSW) occurred during the winter were contrasted with years without such events and composited through superposed epoch analysis. The results show that EPWs are a ubiquitous—and unexpected—feature of meridional wind variability near 95 km. Present even in non-ES-SSW years, they display a regular annual cycle peaking in January or February, depending on the zonal wavenumber. In years when an ES-SSW occurred, the EPWs were highly variable but enhanced before and after the onset. [ABSTRACT FROM AUTHOR]

The age of air is an important transport diagnostic that can be derived from trace gas measurements and compared to global chemistry climate model output. We describe a new technique to calculate the age of air, measuring transport times from the Earth's surface to any location in the atmosphere based on simultaneous in situ measurements of multiple key long-lived trace gases. The primary benefits of this new technique include (1) optimized ages of air consistent with simultaneously measured SF6 and CO2 ; (2) age of air from the upper troposphere through the stratosphere; (3) estimates of the second moment of age spectra that have not been well constrained from measurements; and (4) flexibility to be used with measurements across multiple instruments, platforms, and decades. We demonstrate the technique on aircraft and balloon measurements from the 1990s, the last period of extensive stratospheric in situ sampling, and several recent missions from the 2020s, and compare the results with previously published and modeled values. [ABSTRACT FROM AUTHOR]

Variability in the stratosphere, especially extreme events such as sudden stratospheric warmings (SSWs), can impact surface weather. Understanding stratospheric prediction uncertainty is therefore crucial for skillful surface weather forecasts on weekly to monthly timescales. Using ECMWF subseasonal hindcasts, this study finds that stratospheric uncertainty is most strongly linked to tropospheric uncertainty over the North Pacific and Northern Europe, regions that can modulate but also respond to stratospheric variability, suggesting a two-way propagation of uncertainty. A case study of the 2018 SSW event shows an initial poleward and upward propagation of uncertainty from tropical convection, followed by a downward propagation where ensemble members that accurately predict the SSW are also better at predicting its downward impacts. These findings highlight the locations in the troposphere that are linked to stratospheric uncertainty and suggest that improved model representation of tropospheric mechanisms linked to polar vortex variability could enhance both stratospheric and extratropical surface prediction. [ABSTRACT FROM AUTHOR]

A scientific balloon is the ideal platform for carrying out long-duration missions for scientific research in the stratosphere. However, when a scientific balloon ascends through icy clouds and reaches supercooled droplets, there is a risk of ice accretion on the balloon's surface. Ice accretion on the balloon can threaten flight safety and the accomplishment of missions and can even result in disastrous accidents. A comprehensive simulation platform was developed to simulate the influence of ice accretion on the thermodynamic performance of a scientific balloon to provide quantitative data support for balloon design and flight operations. The simulation platform consisted of two parts: one based on ANSYS software to solve the accretion model and the other a program developed with MATLAB software to solve the thermodynamic model. The results suggest that, in certain cloud environments, there is a risk of ice accretion on a balloon's surface; the extra ice mass added to the balloon may prevent it from ascending through icy clouds and instead keep it floating at the base of these clouds. [ABSTRACT FROM AUTHOR]

Long path length FTIR‐smog chamber techniques were used to study the title reactions in 650 Torr of N2, oxygen, or air diluent at 296 ± 3 K. Values of k(Cl + (Z)‐CF2HCF = CHCl)═(6.6 ± 0.7) × 10−11 and k(OH + (Z)‐CF2HCF═CHCl)═(4.1 ± 0.7) × 10−12 cm3 molecule−1 s−1 were measured. The IR spectrum of (Z)‐CF2HCF═CHCl is reported. The atmospheric lifetime of (Z)‐CF2HCF═CHCl is determined by the reaction with OH and is approximately 2.8 days. Reaction of (Z)‐CF2HCF═CHCl with Cl atoms gives HC(O)Cl and CF2HC(O)F as major primary products. Under environmental conditions, the OH radical initiated oxidation gives CF2HC(O)F and HC(O)Cl in yields of (98 ± 8)% and (100 ± 4)%, respectively. Accounting for non‐uniform horizontal and vertical mixing leads to a 100‐year time‐horizon global warming potential value for (Z)‐CF2HCF═CHCl of essentially zero. [ABSTRACT FROM AUTHOR]

Abstract Control of the geographic location of high-altitude balloons has been desired for decades due to the cost and simplicity of the systems. These balloon systems rely on variations in wind direction with altitude so that when a balloon changes height, it also changes the direction of its horizontal motion. An altitude control system can thus also control the horizontal position by transitioning to a wind layer with favorable winds. The system’s ability to navigate successfully thus relies on the existence of certain wind conditions. In this paper, we explore how the ability of a balloon to station-keep varies based on the geographic location and season. We used spatially and temporally variant ERA5 wind data with a tree-search-based algorithm to traverse potential trajectories, and we selected the altitude transitions that maximize time within 50 km of a target. The simulation’s outputs show large variations in success across both latitude and season. Midlatitudes are particularly challenging for station-keeping, while lower latitudes are more favorable. Summer is typically more favorable than winter. This demonstrates that for all balloon systems, the ability to station-keep is highly variant and not universally possible.

This study evaluates the climatology and trends of the Brewer–Dobson circulation (BDC) in the Japanese Reanalysis for Three Quarters of a Century (JRA‐3Q) reanalysis compared with those in the Japanese 55‐year reanalysis (JRA‐55) and ERA5 reanalyses. The spatial structure of the BDC shows good agreement among the reanalyses. However, zonal mean tropical upwelling near the lower stratosphere in JRA‐3Q is approximately 80% of that in JRA‐55 throughout the reanalysis period. The long‐term trend of BDC intensity for the period 1948–2022 showed a slight increase in JRA‐3Q and in JRA‐55, whereas that in ERA5 decreased. To investigate the cause of the difference in tropical upwelling between JRA‐3Q and JRA‐55, data assimilation sensitivity experiments were conducted by modifying the forecast model used in the data assimilation system. These results indicate that the difference in BDC intensity between JRA‐3Q and JRA‐55 can be primarily attributed to diabatic heating in the tropical troposphere produced in the forecast model. However, the difference between JRA‐3Q and ERA5 cannot be accounted for by diabatic heating in the forecast model. It is also found that the implementation of the non‐orographic gravity wave drag parameterisation scheme in the JRA forecast model is not the reason for the weaker BDC in JRA‐3Q. [ABSTRACT FROM AUTHOR]

Accurate representation of near‐tropopause fields is important for the forecast skill of numerical weather prediction models, yet there remain significant systematic forecast errors in the region of the tropopause. Although extratropical near‐tropopause humidity, temperature, and wind model biases have been documented from several models, more knowledge of their causes is required as a step towards reducing these biases. Typically, a moist bias is present in the lowermost stratosphere in the analyses used to initialise forecasts, which leads to a growing cold bias in the lowermost stratosphere over the course of the forecasts due to long‐wave radiative cooling. Experiments are conducted with the European Centre of Medium‐Range Weather Forecasts global forecast system where the humidity in a layer 0–4 km above the tropopause in the extratropics is reduced to correct the moist bias in the initial conditions. In these experiments, the lowermost stratosphere cold bias growth is halved compared with the control and gradually remoistens, returning to typical analysis values with a half‐life of around 8–9 days. The reduction in cooling in the lowermost stratosphere is due to a reduction in long‐wave radiative emission from the water vapour above the tropopause. The main contributors to the remoistening are resolved advective transport and parametrised turbulent mixing in the model, the cloud microphysical process rates being similar in the modified and control experiments. The biases in near‐tropopause moisture transport are almost independent of horizontal resolution. These results show that the temperature bias in the extratropical lower stratosphere can be reduced by correcting the collocated moist bias, but the moist bias cannot be fixed by solely correcting the initial conditions and further model improvements are also required to reduce cross‐tropopause moisture transport. [ABSTRACT FROM AUTHOR]

During northern winter the stratospheric polar vortex is highly variable — even breaking down completely during sudden stratospheric warmings. The strength of the stratospheric polar vortex is observed to be coupled to surface weather, primarily through swings in the phase of the Northern Annular Mode — which is nearly uuivalent to polar‐cap sea‐level pressure. Pressure changes (as a function of height) are largest at the surface, which is difficult to reconcile with the remote effects of stratospheric variability. This conundrum requires some mechanism(s) to amplify the polar sea‐level pressure anomalies. A simple, intuitive explanation has remained elusive. We use Japanese 55‐year Reanalysis (JRA‐55) reanalyses to investigate the reason that stratospheric variability causes large polar sea‐level pressure changes. The main result of this paper is that vertical movement of the polar tropopause is essential in understanding how surface pressure changes are generated. The strength of the polar vortex is strongly coupled to the height of the polar tropopause, resulting in stretching/compression of the polar tropospheric air column. This causes pressure changes that are largest at the surface. For example, the lowering of the polar tropopause during a sudden stratospheric warming leads to a compression and spin down of the tropospheric column and is therefore associated with higher polar sea‐level pressure. This mechanism can be compared to the textbook example of conservation of potential vorticity as an air column moves over a mountain range — except in this case the column depth changes because the stratosphere is changing the height of the tropopause. The observed vertical profile of pressure changes matches closely what would be expected from the stretching/compression mechanism. The higher polar sea‐level pressure associated with a sudden stratospheric warming is due mainly to mass moving into the polar cap within the troposphere, rather than rearranged mass in the stratosphere. [ABSTRACT FROM AUTHOR]

Accurate wind speed measurement in low-pressure conditions is crucial for the thermal performance validation and attitude control of stratospheric aircraft. As air density decreases, traditional wind speed measurement systems based on principles such as dynamic pressure, heat transfer, ultrasound, and particle velocimetry face significant challenges when applied in low-pressure environments, often failing to achieve the required measurement accuracy. This paper presents the development of a wind speed simulation system based on a rotation method designed to operate in low-pressure conditions, utilizing a space environment simulation chamber in conjunction with a high-precision turntable. The system was employed to conduct response tests on a constant heat flow thermal sphere anemometer within a stratospheric pressure range of 1 kPa to 30 kPa. The experimental results revealed that at extremely low Reynolds numbers, the probe signal exhibited increasing nonlinearity, significantly affecting the response curve at pressures below 15 kPa. While the sensitivity of the hot-sphere probe remained relatively stable at wind speeds above 5 m/s, it decreased nonlinearly as the pressure dropped when wind speeds fell below 5 m/s. Furthermore, this paper analyzes the impact of various interpolation methods on wind speed conversion errors, providing valuable data to support the future development and validation of stratospheric aircraft. [ABSTRACT FROM AUTHOR]

Molecular scattering (Rayleigh scattering) has been extensively used from the ground with lidars and from space to observe the limb, thereby deriving vertical temperature profiles between 30 and 80 km. In this study, we investigate how temperature can be measured using the new Ozone Mapping and Profiler Suite (OMPS) sensor, aboard the Suomi NPP and NOAA-21 satellites. The OMPS consists of three instruments whose main purpose is to study the composition of the stratosphere. One of these, the Limb Profiler (LP), measures the radiance of the limb of the middle atmosphere (stratosphere and mesosphere, 12 to 90 km altitude) at wavelengths from 290 to 1020 nm. This new data set has been used with a New Simplified Radiative Transfer Model (NSRTM) to derive temperature profiles with a vertical resolution of 1 km. To validate the method, the OMPS-derived temperature profiles were compared with data from four ground-based lidars and the ERA5 and MSIS models. The results show that OMPS and the lidars are in agreement within a range of about 5 K from 30 to 80 km. Comparisons with the models also show similar results, except for ERA5 beyond 50 km. We investigated various sources of bias, such as different attenuation sources, which can produce errors of up to 120 K in the UV range, instrumental errors around 0.8 K and noise problems of up to 150 K in the visible range for OMPS. This study also highlighted the interest in developing a new miniaturised instrument that could provide real-time observation of atmospheric vertical temperature profiles using a constellation of CubeSats with our NSRTM. [ABSTRACT FROM AUTHOR]

The 2022 Hunga eruption caused unprecedented stratospheric hydration. Aura Microwave Limb Sounder (MLS) measurements show that the stratospheric water vapor mass remains essentially unchanged as of early 2024 and that the Hunga hydration occurred atop a robust (possibly accelerating) moistening trend in the stratosphere. Enhanced by the excess Hunga water vapor, dehydration via polar stratospheric cloud sedimentation in the 2023 Antarctic vortex exceeded climatological values by ∼ ${\sim} $50%. Simple projections based on modeled exponential decay illustrate that the timing of the return to humidity levels that would have been expected absent the Hunga hydration depends on the ongoing stratospheric water vapor trend. With the Hunga hydration compounding an underlying moistening trend, the stratosphere could remain anomalously humid for an extended period. Plain Language Summary: The 2022 Hunga eruption injected an unprecedented amount of water vapor directly into the very dry stratosphere. This abrupt increase in water vapor from Hunga occurred at a time when the stratosphere was already gradually becoming moister. Using measurements from the Microwave Limb Sounder (MLS) on NASA's Aura satellite, we show that stratospheric water vapor remained elevated, essentially unchanged, from the time of the eruption until at least early 2024. MLS data further reveal that, in 2023, one of the main mechanisms for drying the stratosphere—permanent removal of water vapor by formation and settling of ice polar stratospheric cloud particles over Antarctica—was substantially more effective than usual, boosted by the excess water vapor from Hunga. Projections indicate that the return to moisture levels that would have been expected in the absence of the eruption depends on how humid the stratosphere continues to get. Considering the ongoing moistening trend and the water vapor injected by Hunga, the stratosphere could remain unusually humid for a considerable period. Key Points: The stratospheric water vapor mass has remained essentially unchanged since the Hunga hydration through at least early 2024Fueled by excess Hunga water vapor, 2023 Antarctic vortex polar stratospheric cloud dehydration exceeded the climatological mean by ∼50%Given its robust (and potentially accelerating) background moistening trend, the stratosphere could stay anomalously humid for years [ABSTRACT FROM AUTHOR]

Temperature fluctuations induced by mountain waves can play a crucial role in the formation of polar stratospheric clouds (PSCs). In particular, the cold phase of the waves can lower local temperatures sufficiently to trigger PSC formation, even when large-scale background temperatures are too high. To provide new quantitative constraints on the relevance of this effect, this study analyzes a decade (2002–2012) of ice PSC detections obtained from Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurements and ERA5 data in the polar winter lower stratosphere. In the MIPAS observations, we find that approximately 52 % of the Arctic ice PSCs and 26 % of the Antarctic ice PSCs are detected at temperatures above the local Tice. Ice PSCs above Tice are concentrated around mountainous regions and their downwind directions. A backward-trajectory analysis is performed to investigate the temperature history of each ice PSC observation. The cumulative fraction of ice PSCs above Tice increases as the trajectory gets closer to the observation point. The most significant change in the fraction of ice PSCs above Tice occurs within the 6 h preceding the observations. At the observation point, the mean fractions of ice PSCs above Tice , taking into account temperature fluctuations along the backward trajectory, are 33 % in the Arctic and 9 % in the Antarctic. The results provide a quantitative assessment of the occurrence of ice PSCs above Tice in connection with orographic waves. Additionally, the observational statistics presented can be utilized for comparison with chemistry climate simulations. [ABSTRACT FROM AUTHOR]

GNSS (Global Navigation Satellite System) Radio Occultation (RO) data is an important component of numerical weather prediction (NWP) systems. To incorporate more GNSS RO data into NWP systems, commercial RO data has become an excellent option. Tianjin Yunyao Aerospace Technology Co., Ltd. (YUNYAO) plans to launch a meteorological constellation of 90 satellites equipped with GNSS-RO instruments, which will significantly increase the amount of GNSS-RO data in NWP systems. This study evaluates the quality of neutral atmosphere refractivity profiles from YUNYAO satellites Y003 to Y010 during the period from May 1 to July 31, 2023. Compared with the refractivity calculated from ERA5, the absolute value of the mean bias (MB) for YUNYAO refractivity data is generally less than 1.5 % between 0 and 40 km, and close to 0 between 4 and 40 km. The standard deviation (SD) is less than 3.4 %, and there are differences in the SDs for different GNSS satellites, especially in the lower troposphere and the stratosphere. Second, the refractivity error SD of YUNYAO RO data is estimated using the 'three-cornered hat' (3CH) method and multiple data sets. In the pressure range of 1000–10 hPa, the refractivity error SD of YUNYAO RO data is below 2.6 %, and the differences in refractivity error SD among different GNSS satellites do not exceed 0.5 %. Finally, compared to COSMIC-2 and Metop-C RO data, YUNYAO RO data exhibit consistent refractivity error SD and are smaller within 300–50 hPa. [ABSTRACT FROM AUTHOR]

Subseasonal forecast models are shown to suffer from the same inconsistency in the signal‐to‐noise ratio evident in climate models. Namely, predictable signals in these models are too weak, yet there is a relatively high level of agreement with observed variability of the atmospheric circulation. The net effect is subseasonal forecast models show higher correlation with observed variability than with their own simulations; that is, the signal‐to‐noise paradox. Also, similar to climate models, this paradox is particularly evident in the North Atlantic sector. The paradox is not evident in week 1 or week 2 forecasts, and hence is limited to subseasonal time‐scales. The paradox appears to be related to an overly fast decay of northern annular mode regimes. Three possible causes of this overly fast decay and for the paradox in the Northern Hemisphere are identified: a too‐fast decay of polar stratospheric signals, overly weak downward coupling from the stratosphere to the surface in some models, and overly weak transient synoptic eddy feedbacks. Though the paradox is clearly evident in the North Atlantic, it is relatively muted in the Southern Hemisphere: southern annular mode regimes persist realistically, the stratospheric signal is well maintained, and eddy feedback is, if anything, too strong and zonal. [ABSTRACT FROM AUTHOR]

We provide a description and concise evaluation of the European Centre of Medium‐range Weather Forecasts Reanalysis v.5 (ERA5) global reanalysis from an additional extension back to 1940 that was released in March 2023, including its timely updates to the end of 2022. The ERA5 product from 1979 to end 2020 and a preliminary back extension from 1950 to 1978 have already been described elsewhere. The new back extension that spans 1940 to 1978 represents the official release and supersedes the preliminary product. Currently, the ERA5 data record extends over more than 83 years of hourly global three‐dimensional fields for many quantities that describe the global atmosphere, land surface, and ocean waves at a horizontal resolution of about 31 km. ERA5 relies on the ingestion of sub‐daily in‐situ and satellite observations, and the number of these increases from 17,000 per day in 1940 to 25 million per day by 2022. Accordingly, the quality of the reanalysis improves throughout the period. Over the Northern Hemisphere ERA5 generally provides a reliable representation of the synoptic situation from the early 1940s and provides long‐term variability that is in line with other datasets. Over the Southern Hemisphere, however, for the early period the description of ERA5 seems mainly statistical. Furthermore, there is a small deviation in surface temperature compared with reconstructions based on monthly aggregations of observations over land before 1946. For this period, the absence of upper air temperature observations reveals a model cold bias in the lower stratosphere. For the period from 1950 to 1978, the final release described here improves on the suboptimal treatment of International Best Track Archive for Climate Stewardship observations in the preliminary release, with, as a result, a much more homogeneous representation of tropical cyclones over the entire ERA5 record. Longer spin‐up periods also have a beneficial impact on soil moisture. [ABSTRACT FROM AUTHOR]

The rate of rocket launches is accelerating, driven by the rapid global development of the space industry. Rocket launches emit gases and particulates into the stratosphere, where they impact the ozone layer via radiative and chemical processes. We create a three‐dimensional per‐vehicle inventory of stratospheric emissions, accounting for flight profiles and all major fuel types in active use (solid, kerosene, cryogenic and hypergolic). In 2019, stratospheric (15–50 km) rocket launch emissions were 5.82 Gg CO2 ${\mathrm{C}\mathrm{O}}_{2}$, 6.38 Gg H2 ${\mathrm{H}}_{2}$O, 0.28 Gg black carbon, 0.22 Gg nitrogen oxides, 0.50 Gg reactive chlorine and 0.91 Gg particulate alumina. The geographic locations of launch sites are preserved in the inventory, which covers all active launch sites in 2019. We also report the emissions data from contemporary vehicles that were not launched in 2019, so that users have freedom to construct their own launch activity scenarios. A subset of the inventory—stratospheric emissions for successful launches in 2019—is freely available and formatted for direct use in global chemistry‐climate or Earth system models. Plain Language Summary: Many governments and companies have expressed bold ambitions to grow their presence in space. However, rocket launches throw out a stream of air pollutants from their burnt fuel as they pass through the stratosphere, which is where the protective ozone layer resides. Currently, launch operators do not have to measure the impacts of their activities on the ozone layer. We gather together all the publicly available information on rocket launches in 2019, from 18 active spaceports worldwide, and make some careful assumptions to convert each rocket's fuel to its burnt fuel products left in the atmosphere. We encourage modeling groups to use our inventory for studies on how rocket launches may impact the ozone layer. Key Points: We compile a comprehensive emissions inventory of all rocket launches in 2019 at 18 active spaceportsIt itemizes chemically and radiatively active species that are produced by the main rocket fuels (kerosene, cryogenic, solid and hypergolic)We discuss the inventory's uncertainties and its usage in global models to study the impacts of rocket launches on the ozone layer [ABSTRACT FROM AUTHOR]

This study presents the first attempt to simulate a full cycle of the quasi‐biennial oscillation (QBO) in a global storm‐resolving model (GSRM) that explicitly simulates deep convection and gravity waves instead of parameterizing them. Using the Icosahedral Nonhydrostatic (ICON) model with horizontal and vertical resolutions of about 5km $5\,\mathrm{k}\mathrm{m}$ and 400m $400\,\mathrm{m}$, respectively, we show that an untuned state‐of‐the‐art GSRM is already on the verge of simulating a QBO‐like oscillation of the zonal wind in the tropical stratosphere for the right reasons. ICON shows overall good fidelity in simulating the QBO momentum budget and the downward propagation of the QBO jets in the upper QBO domain (25–35 km). In the lowermost stratosphere, however, ICON does not simulate the downward propagation of the QBO jets to the tropopause. This is the result of a pronounced lack of QBO wave forcing, mainly on planetary scales. The lack of planetary‐scale wave forcing in the lowermost stratosphere is caused by an underestimation of planetary‐scale wave momentum fluxes entering the stratosphere. We attribute this lack of planetary‐scale wave momentum fluxes to a substantial lack of convectively coupled equatorial waves (CCEWs) in the tropical troposphere. Therefore, we conclude that in ICON, simulating a realistic spatio‐temporal variability of tropical deep convection, in particular CCEWs, is currently the main roadblock toward simulating a reasonable QBO. To overcome this intermediate situation, we propose to aim at an improved explicit simulation of tropical deep convection by retuning the remaining parameterizations of cloud microphysics and vertical diffusion, and by increasing the horizontal resolution. Plain Language Summary: The quasi‐biennial oscillation (QBO) is a wind system located in the equatorial stratosphere between ∼17 ${\sim} 17$ and ∼35km ${\sim} 35\hspace*{.5em}\mathrm{k}\mathrm{m}$ and consists of westerly and easterly wind jets that alternately propagate downward with time. The QBO has been shown to influence surface weather, so it is important to simulate the QBO realistically in the computer models typically used for climate research. However, these models often struggle to simulate a realistic QBO because they represent the processes leading up to the QBO, that is, tropical rain showers and short atmospheric waves excited by these rain showers, only empirically through so‐called parameterizations. In this study, we attempt for the first time to simulate the QBO in a model that directly represents these processes through an ultra‐fine grid. We find that our model maintains QBO‐like stratospheric winds throughout the simulation, and in the central stratosphere, the model simulates the characteristics of the QBO reasonably well for the right reasons. However, in the lowermost stratosphere, the simulated QBO is not realistic and does not move downward with time as observed due to a misrepresentation of long waves in the tropical atmosphere. These results will guide future model development to improve the model's representation of the QBO. Key Points: The ability of the general circulation model ICON, which explicitly simulates deep convection and gravity waves, to simulate a quasi‐biennial oscillation (QBO) is testedICON simulates a reasonable downward propagation and momentum balance of QBO‐like jets in the upper QBO domain in the first simulation yearSimulated QBO‐like jets stall in lower QBO domain due to a lack of planetary wave forcing due to weak convectively coupled equatorial waves [ABSTRACT FROM AUTHOR]

This study is dedicated to the investigation of the relationship between the wave activity in February and temperature variations in the Arctic lower stratosphere in March. To study this relationship, the correlation coefficients (CCs) between the minimum temperature of the Arctic lower stratosphere in March (Tmin) and the amplitude of the planetary wave with zonal number 1 (PW1) in February were calculated. Tmin determines the conditions for the formation of polar stratospheric clouds (PSCs) following the chemical destruction of the ozone layer. The NCEP and ERA5 reanalysis data and the modern and future climate simulations of the Earth system models INM CM5 and SOCOLv4 were employed. It is shown that the maximum significant CC value between Tmin at 70 hPa in the polar region in March and the amplitude of the PW1 in February in the reanalysis data in the lower stratosphere is 0.67 at the pressure level of 200 hPa. The CCs calculated using the model data are characterized by maximum values of ~0.5, also near the same pressure level. Thus, it is demonstrated that the change in the planetary wave activity in the lower extratropical stratosphere in February can be one of the predictors of the Tmin. For further analysis of the dynamic structure in the lower stratosphere, composites of 10 seasons with the lowest and highest Tmin of the Arctic lower stratosphere in March were assembled. For these composites, differences in the vertical distribution and total ozone content, surface temperature, and residual meridional circulation (RMC) were considered, and features of the spatial distribution of wave activity fluxes were investigated. The obtained results may be useful for the development of forecasting of the Arctic winter stratosphere circulation, especially for the late winter season, when substantial ozone depletion occurs in some years. [ABSTRACT FROM AUTHOR]

On October 9, 2022, orbiting X-ray and γ-ray telescopes registered the most powerful explosion ever observed in the Universe—the GRB221009A γ-ray burst at a distance of 2.4 billion light years. The response of the Earth's ionosphere to this unique event was detected in the received signals of very-low-frequency (VLF) radio paths passing through both the daytime and nighttime ionosphere. A disturbance in the night sector was observed as a sudden decrease in amplitude up to 7 dB and a sharp jump in the signal phase up to 20°‒30°. Less pronounced amplitude jumps up to 1.5 dB were found in the daytime sector. At the time of the flare, magnetometers showed only the appearance of a weak burst of the geomagnetic field ∼0.5 nT at the time of the flare. In the daytime, an isolated geomagnetic pulse with an amplitude of up to 1 nT was observed. The appearance of a geomagnetic response to a γ-ray flare is surprising, because its radiation creates additional ionization in the stratosphere, significantly below the conducting E-layer of the ionosphere. The recorded event showed that extragalactic γ-ray bursts cause a noticeable perturbation in the Earth's ionosphere, and the network of VLF radio paths covering the lower ionosphere can be considered as a giant γ-ray detector. [ABSTRACT FROM AUTHOR]

This study focuses on the impact of the stratospheric quasi-biennial oscillation (QBO) on the early stage of the Indian summer monsoon (ISM) in May and June, which has thus far been an ambiguous topic of research. It is found that the 50-hPa QBO in the preceding winter and spring is significantly and negatively correlated with precipitation in the southern Arabian Sea and central India in May, which shifts northward to northern India in June. This correlation is nearly the opposite for the 10-hPa and 20-hPa QBO. An easterly phase of the 50-hPa QBO corresponds to a colder and higher tropopause over the subtropical ISM region which is related to vigorous convection over India. Meanwhile, the QBO-related meridional dipole pattern of zonal wind from the stratosphere to troposphere in the subtropics and mid-latitudes connects to an anomalous high in the upper troposphere across the subtropical land and the northern Arabian Sea, which causes an anomalous descent and in situ adiabatic heating. This heating supports an enhanced meridional land-sea thermal contrast and thus an early and strong ISM. The situation for westerly 50-hPa QBO is generally the opposite. The climate models from the Coupled Model Intercomparison Project Phases 6 (CMIP6) can generally reproduce the QBO–ISM relationship in June (but not in May), though with some discrepancies from the observation. Inter-model comparison demonstrates that better representation of the QBO–ISM correlation depends well on a better simulation of the QBO-related meridional dipole of zonal wind in the subtropical ISM region. [ABSTRACT FROM AUTHOR]

Previous study has revealed the possible linear superposition of the El Niño-Southern Oscillation (ENSO) and Quasi-Biennial Oscillation (QBO)'s impacts on the northern winter stratosphere. This study first assesses the reproducibility of stratospheric ENSO and QBO teleconnections by 18 models able of producing QBO from the Coupled Model Intercomparison Project Phase (CMIP)-5 and CMIP6. Based on different teleconnection indices, high-skill models are adopted to reexamine the extratropical response to four ENSO-QBO configurations (El Niño-QBO easterly (EQBO), El Niño-QBO westerly (WQBO), La Niña-QBO easterly, and La Niña-QBO westerly). The modelling evidence validates that the stratospheric ENSO (QBO) signal can be separated by selecting major events based on the corresponding index and subtracting the QBO (ENSO) signal from model outputs through the regression method. The composite stratospheric response to a specific ENSO-QBO configuration is almost identical to the summation of impacts of individual QBO and ENSO, which validates the linearity. This study offers novel model evidence that stratospheric ENSO and QBO's teleconnections exhibit strong linearity in the northern winter. This linearity also exists in the troposphere to some degree. During the composite compound El Niño-EQBO conditions, the stratospheric polar vortex (SPV) weakens and is warmer, and its strengthening and cold anomalies also enlarge for the composite compound La Niña-WQBO conditions due to their cooperative amplification of signals by both QBO and ENSO. In contrary, the sign of the composite polar stratospheric total response is mainly determined by the QBO phase in both El Niño-WQBO and La Niña-EQBO composites. [ABSTRACT FROM AUTHOR]

Previous studies have reported a close relationship between the negative Arctic Oscillation (AO) and the PM2.5 (particulate matter with a diameter of 2.5 µm or less) diffusion in North China in winter. Using the North China regional mean meridional wind at 850 hPa derived from the ERA5 (ECMWF Reanalysis version 5) reanalysis data in 1979–2022 as a useful substitute for station observed PM2.5 concentration (since the latter is available only since 2014), our study detected strong/weak northerly events representing the abnormal PM2.5 diffusion/accumulation events, and revisited the AO–PM2.5 diffusion relationship in North China during 1979–2022. The results show that only when the AO was characterized by a 2-month continuously negative/positive phases and with twin peaks respectively before and after the diffusion/accumulation events, would there be higher occurrences of the abnormal PM2.5 diffusion/accumulation. The second peak of negative AO acted to prolong the strong northerly winds by an average of 2 days. Further analysis reveals that the AO with twin peaks always has a footprint in the stratospheric northern annular mode (NAM) during the abnormal PM2.5 events, and the coupling between the stratosphere and troposphere plays a critical role in the second peak of AO. Vertical propagation of baroclinically amplifying waves leads to changes in isentropic meridional mass fluxes in the stratosphere following the changes in the troposphere. The stronger/weaker poleward mass fluxes increase/decrease the polar mass in the stratosphere, which dominates the total column air mass changes and leads to the second peak of AO. Considering the subseasonal predictability of the stratospheric NAM based on existing evidence, particular attention should be paid to these AO-related abnormal PM2.5 diffusion and accumulation events in North China because they might be more predictable at a longer lead time. [ABSTRACT FROM AUTHOR]

The tropopause is an important transition layer and can be a diagnostic of upper-tropospheric and lower-stratospheric structures, exhibiting unique atmospheric thermal and dynamic characteristics. A comprehensive understanding of the evolution of fine tropopause structures is necessary and primary for the further study of complex multi-scale atmospheric physical–chemical coupling processes in the upper troposphere and lower stratosphere. A novel method utilizing the bi-Gaussian function is capable of identifying the characteristic parameters of vertical tropopause structures and providing information on double-tropopause (DT) structures. The new method improves the definition of the cold-point tropopause and detects one (or two) of the most significant local cold points by fitting the temperature profiles to the bi-Gaussian function, which defines the point(s) as the tropopause height(s). The bi-Gaussian function exhibits excellent potential for explicating the variation trends of temperature profiles. The results of the bi-Gaussian method and lapse rate tropopause, as defined by the World Meteorological Organization, are compared in detail for different cases. Results indicate that the bi-Gaussian method is able to more stably and obviously identify the spatial and temporal distribution characteristics of the thermal tropopauses, even in the presence of multiple temperature inversion layers at higher elevations. Moreover, 5 years of historical radiosonde data from China (from 2012 to 2016) revealed that the occurrence frequency and thickness of the DT, as well as the single-tropopause height and the first and second DT heights, displayed significant meridional monotonic variations. The occurrence frequency (thickness) of the DT increased from 1.07 % (1.96 km) to 47.19 % (5.42 km) in the latitude range of 16–50° N. The meridional gradients of tropopause height were relatively large in the latitude range of 30–40° N, essentially corresponding to the climatological locations of the subtropical jet and the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The stratospheric polar vortex (SPV) significantly influences current weather and climate patterns. However, its state in the geological past remains largely unexplored. This study investigates SPV variations in the past 250 million years, using a fully coupled Earth System Model. It is found that midlatitude paleogeography primarily drove substantial SPV variations in the deep time, while changes in CO2 concentrations and solar insolation play a minor role. Both the Arctic and Antarctic SPV were strengthened when the supercontinent Pangea broke up. The increased asymmetry of midlatitude land‐sea contrast tended to weaken the upward propagation of wavenumber‐1 planetary waves, thereby strengthening the SPV. This SPV strengthening correlated with the decelerated stratospheric Brewer‐Dobson circulation and uplift of the polar tropopause. Our results highlight the crucial role of paleogeography in regulating SPV variations and stratosphere–troposphere coupling in deep‐time climate. Plain Language Summary: At present, influences of the stratospheric polar vortex (SPV) on surface climate have attracted growing attention. In the geological past, however, how the SPV acted and how it impacted on the troposphere and surface climate remains unclear. This study explores SPV variations in both the Northern and Southern Hemispheres in the past 250 million years (Myr) using simulations of a fully coupled Earth System Model. Our results reveal that polar stratospheric temperatures fluctuated by up to 20 K in the geological past, which is much greater than the variations from 1850 to the present. Midlatitude paleogeography played a crucial role in SPV variations over tectonic timescales. The breakup and drift of the Pangea supercontinent altered the upward propagation of Rossby waves from the troposphere into the stratosphere. It influenced not only the SPV but also the strength of stratospheric Brewer‐Dobson circulation as well as the polar tropopause height. This work helps to understand the role of paleogeography in the stratosphere. Key Points: The stratospheric polar vortex (SPV) experienced dramatic variations in the past 250 million yearsMidlatitude paleogeography has a crucial impact on SPV variations by regulating upward propagation of planetary wavesThe SPV variation is closely associated with changes in stratospheric Brewer‐Dobson circulation over tectonic timescales [ABSTRACT FROM AUTHOR]

Observations of March 2024 Arctic (63°N–90°N) total column ozone set a record high of 477 Dobson Units (DU) against the 1979–2023 satellite era time series. It was about 60 DU higher than average and 6 DU higher than the previous March 1979 471 DU record. Daily Arctic ozone was above average for every day in March 2024, and set record highs from 11–26 March 2024. Microwave Limb Sounder data show this record ozone anomaly was concentrated in the lower stratosphere (10–30 km). These record values developed over the 2023–2024 winter and can be associated with vertically propagating planetary‐scale wave events that caused significant stratospheric warmings. These wave events forced poleward and downward ozone advection into the lower stratosphere, leading to record column ozone levels. The above average levels persisted through August 2024 and across the northern hemisphere. Plain Language Summary: Man‐made chlorofluorocarbons (CFCs) depleted the Earth ozone layer. The 1987 Montreal Protocol curbed CFC growth, but because CFCs have multi‐decadal lifetimes, Arctic ozone is not expected to recover back to 1980 levels until ∼2045. Current high CFC levels combined with persistent and cold polar vortices led to severe Arctic ozone spring depletion in 1997, 2011, and 2020. Contrary to expectations, March 2024 Arctic ozone showed a record high level, dramatically contrasting against the severe depletion events. Meteorological and ozone profile information show that the exceptional 2024 ozone was mainly found in the lowermost Arctic stratosphere, in association with record high lowermost stratospheric temperatures. The ozone levels incrementally increased during the 2023–2024 winter because of large‐scale weather systems that propagated from the troposphere into the stratosphere. Collectively, these weather systems also were at a record level, moving higher ozone concentrations from the mid‐latitudes and upper stratospheric into the Arctic region. This record high ozone would likely have not occurred if CFC levels had not begun slowly declining in response to the Montreal Protocol. Given the absence of high Arctic ozone since the 1970s, the March 2024 record high should be considered a positive harbinger of the future Arctic ozone layer. Key Points: Arctic total column ozone in March 2024 set a record high for the 1979‐present periodPolar lower stratosphere temperatures also set a record high in March 2024 in the MERRA‐2 reanalysis dataA record amount of Rossby waves propagating upward from the troposphere caused the record total ozone and lower stratospheric temperature [ABSTRACT FROM AUTHOR]

The dynamical environment of the stratosphere, during the summer over North America, provides a natural integrator of the impact of convection in the lower stratosphere, as air can be confined for periods of a few days to more than a week. In situ data obtained during the NASA Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) field campaign show increasing water vapor mixing ratios in background air as a function of time the air parcel spent within the North American Monsoon Anticyclone region. We find that water vapor added to the stratosphere by convection decreases with altitude and tends to drop below detectable limits by the 415 K isentrope in 2021 and the 430 K isentrope in 2022. Integrating between potential temperatures of 380 and 460 K we find that convection added between 20 and 32 Tg per summer to the stratosphere in 2021 and 2022. While the total amount is only 1%–4% of the amount ascending in the tropics across the tropical tropopause, small changes in the annual flux of water can have a significant effect on the radiation budget of the atmosphere. Locally, over North America we find that convection increased the water vapor mixing ratio at 380 K by as much as 40%. Tropopause‐penetrating convection is part of the yearly cycle of stratospheric water vapor and we suggest that it must be included in extratropical models to accurately predict future trends in stratospheric water vapor. Plain Language Summary: Water vapor in the stratosphere is important for regulating Earth's climate and also influences the amount of ozone in the stratosphere. Most air rises into the stratosphere through the tropical tropopause where the excess water freezes out leaving very dry air. But air and water can also be injected into the stratosphere via strong convective storm systems. During the summer months, strong storms over the Sierra Madre Occidental and the central United States are known to produce many overshoots that can be seen with radar and satellite. A recent NASA airborne campaign called Dynamics and Chemistry of the Summer Stratosphere (DCOTSS) aimed to study this region. The aircraft was equipped with 12 different sensors measuring gases, aerosols, and meteorological variables. We use these measurements to look at the cumulative effect these storms have on the background air in the stratosphere and specifically calculate the amount of water vapor added by convection as a function of altitude above the tropopause. We find that water added by storms over North America is 1%–4% of the total amount ascending in the tropics. Over North America convection may account for as much as a 40% increase in lower stratospheric water vapor. Key Points: Deep convection over North America lofts significant amounts of water to the lower stratosphereThe North American Monsoon Anticyclone (NAMA) provides a natural integrator of convective perturbations to the stratosphereConvective detrainment of water vapor and ice is quantified by looking at changes in background air as a function of time spent in the NAMA [ABSTRACT FROM AUTHOR]

Atmospheric migrating diurnal tide (DW1) is one of the prominent variabilities in the mesosphere and lower thermosphere (MLT). The existence of the solar cycle dependence of DW1 is debated, and there exist different and even opposite findings at different latitudes. In this paper, the solar cycle dependence of temperature DW1 in the equatorial mesosphere and lower thermosphere (MLT) is investigated using temperature global observations from TIMED/SABER spanning 22 years (2002–2023). The results show that (a) the solar cycle dependence of temperature DW1 is seen very clearly at the equator. The maximum correlation coefficient between DW1 and the F10.7 index occurs at 87km, with 0.72; the second maximum coefficient occurs at 99 km, with 0.62. The coefficient could reach 0.87 at 87 km and 0.67 at 99 km after dropping the years influenced by the Stratosphere Quasi-biennial oscillation (SQBO) disruption event. (b) DW1 shows a lag response to the solar cycle at the equator. DW1 amplitudes show a 1-year lag to the F10.7 index at 87 km and a 2-year lag to the F10.7 index at 99 km. [ABSTRACT FROM AUTHOR]

In this study, we examine eight major boreal sudden stratospheric warming (SSW) events between 2007 and 2019 to understand the vertical coupling between the troposphere and stratosphere as well as the relationship between SSWs and blocking events using global navigation satellite system (GNSS) radio occultation (RO) observations. Our study covers the main aspects of SSW events, including the vertical structure of planetary-wave propagation, static stability, geometry of the polar vortex, and occurrence of blocking events. To analyze wave activity and atmospheric circulation, we compute the quasi-geostrophic Eliassen–Palm (EP) flux and geostrophic winds. The results show that the observations agree with theory and previous studies in terms of the primary dynamic features and provide a detailed view of their vertical structure. We observe a clear positive peak of upward EP flux in the stratosphere prior to all SSW events. In seven out of eight events, this peak is preceded by a clear peak in the troposphere. Within the observed timeframe, we identify two types of downward dynamic interactions and the emergence of blocking events. During the 2007 and 2008 "reflecting" events, we observe a displacement of the polar vortex along with a downward propagation of wave activity from the stratosphere to the troposphere during vortex recovery, coinciding with the formation of blocking in the North Pacific region. Conversely, in the other six SSW "absorbing" events from 2009 to 2019, which were characterized by a vortex split, we observe wave absorption and the subsequent formation of blocking in the Euro-Atlantic region. The analysis of the static stability demonstrates an enhancement of the polar tropopause inversion layer as the result of SSWs, which was stronger for the absorbing events. Overall, our study provides an observational view of the synoptic and dynamic evolution of the major SSWs, their link to blocking, and the impact on the polar tropopause. [ABSTRACT FROM AUTHOR]

The literature presents different views on how the stratosphere influences variability in surface nitrous oxide (N 2 O) and on whether that influence is outweighed by surface emission changes driven by the El Niño–Southern Oscillation (ENSO). These questions are investigated using a chemistry–climate model with a stratospheric N 2 O tracer; surface and aircraft-based N 2 O measurements; and indices for ENSO, polar lower stratospheric temperature (PLST), and the stratospheric quasi-biennial oscillation (QBO). The model simulates well-defined seasonal cycles in tropospheric N 2 O that are caused mainly by the seasonal descent of N 2 O-poor stratospheric air in polar regions with subsequent cross-tropopause transport and mixing. Similar seasonal cycles are identified in recently available N 2 O data from aircraft. A correlation analysis between the N 2 O atmospheric growth rate (AGR) anomaly in long-term surface monitoring data and the ENSO, PLST, and QBO indices reveals hemispheric differences. In the Northern Hemisphere, the surface N 2 O AGR is negatively correlated with winter (January–March) PLST. This correlation is consistent with an influence from the Brewer–Dobson circulation, which brings N 2 O-poor air from the middle and upper stratosphere into the lower stratosphere with associated warming due to diabatic descent. In the Southern Hemisphere, the N 2 O AGR is better correlated to QBO and ENSO indices. These different hemispheric influences on the N 2 O AGR are consistent with known atmospheric dynamics and the complex interaction of the QBO with the Brewer-Dobson circulation. More airborne surveys extending to the tropopause would help elucidate the stratospheric influence on tropospheric N 2 O, allowing for better understanding of surface sources. [ABSTRACT FROM AUTHOR]

The ozone layer is often noted to exhibit self-healing, whereby depletion of ozone aloft induces ozone increases below, explained as resulting from enhanced ozone production due to the associated increase in ultraviolet (UV) radiation below. Similarly, ozone enhancement aloft can reduce ozone below (reverse self-healing). This paper considers self-healing and reverse self-healing to manifest a general mechanism we call photochemical adjustment, whereby ozone perturbations lead to a downward cascade of anomalies in UV and ozone. Conventional explanations for self-healing imply that photochemical adjustment is stabilizing, damping perturbations towards the surface. However, photochemical adjustment can be destabilizing if the enhanced UV disproportionately increases the ozone sink, as can occur if the enhanced UV photolyzes ozone to produce atomic oxygen, which speeds up catalytic destruction of ozone. We analyze photochemical adjustment in two linear ozone models (Cariolle v2.9 and LINOZ), finding that (1) photochemical adjustment is destabilizing above 40 km in the tropical stratosphere and (2) self-healing often represents only a small fraction of the total photochemical stabilization. The destabilizing regime above 40 km is reproduced in a much simpler model: the Chapman cycle augmented with destruction of O and O 3 by generalized catalytic cycles and transport (the Chapman+2 model). The Chapman+2 model reveals that photochemical destabilization occurs where the ozone sink is more sensitive than the source to perturbations in overhead column ozone, which is found to occur when the window of overlapping absorption by O 2 and O 3 is optically unsaturated, i.e., when overhead slant column ozone is below approximately 10 18 molec. cm -2. [ABSTRACT FROM AUTHOR]