Lower Stratosphere Research Articles

Modeling the Radiative Forcing and Atmospheric Temperature Perturbations Caused by the 2022 Hunga Volcano Explosion

AbstractWe model the radiative forcing (RF) of stratospheric sulfate aerosols (SAs) and water vapor (WV) clouds generated by the explosive eruption of the Hunga volcano on 15 January 2022, using the WRF‐Chem meteorology‐chemistry model. We inject 150 Mt of WV and 0.45 Mt of SO2 at a height of 35 km. The resulting volcanic WV layer is cooled through thermal radiation and descends to 27 km in 2 weeks. After the eruption, the WV mixing ratio within the plume exceeds 30 ppmV and gradually reduces thereafter. Within 3 weeks, SO2 is converted to SO4 with a 1.0 μm global stratospheric aerosol optical depth (SAOD) of 0.0025. The SO2 mass should be scaled to 0.73–1.46 Mt to fit the observed SAOD. The 6‐month average global mean net instantaneous RF (IRF) of volcanic SAs at the top of the atmosphere (TOA) reaches −0.381 W/m2 for a 1.46‐Mt SO2 emission. The negative WV net IRF at TOA is at least one order of magnitude in absolute value smaller than that from SAs. The WV IRF at the bottom of the atmosphere is negligibly small and cannot cause discernible long‐term effects on ocean temperature on its own. Cooling in the lower stratosphere within the WV plume exceeds −1 K, and the WV adjusted (to stratospheric temperature) RF (ARF) is positive at TOA and the tropopause but is overwhelmed by negative SA forcing. The patchy tropospheric temperature response does not show notable changes.

Recent Lower Stratospheric Ozone Trends in CCMI‐2022 Models: Role of Natural Variability and Transport

AbstractLower stratospheric ozone between 60°S and 60°N has continued to decline since 1998, despite the reduction of ozone‐depleting substances following the Montreal Protocol. Previous studies have shown that, while chemistry‐climate models reproduce the negative ozone trend in the tropical lower stratosphere as a response to increased upwelling, they fail to capture the ozone decline in northern midlatitudes. This study revisits recent lower stratospheric ozone trends over the period 1998–2018 using two types of simulations from the new Chemistry Climate Model Initiative 2022 (CCMI‐2022): REF‐D1, with observed sea surface temperatures, and REF‐D2, with simulated ocean. The observed negative trend in midlatitudes falls within the range of model trends, especially when considering simulations with observed boundary conditions. There is a large spread in the simulated midlatitudes ozone trends, with some simulations showing positive and others negative trends. A multiple linear regression analysis shows that the spread in the trends is not explained by the different linear response to external forcings (solar cycle, global warming, and ozone‐depleting substances) or to the main variability modes (El Niño‐Southern Oscillation and the quasi‐biennial oscillation) but is instead attributed to internal atmospheric variability. Moreover, the fact that some models show very different trends across members, while other models show similar trends in all members, suggests fundamental differences in the representation of the internal variability of ozone transport across models. Indeed, we report substantial intermodel differences in the ozone‐transport connection on interannual timescales and we find that ozone trends are closely coupled to transport trends.

Impact of wildfire smoke on Arctic cirrus formation – Part 2: Simulation of MOSAiC 2019–2020 cases

Abstract. A simulation study of the potential impact of wildfire smoke on Arctic cirrus formation is presented. The simulations complement the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) field observations, discussed in Part 1 (Ansmann et al., 2025) of this work. The observations suggest that Siberian wildfire smoke had a strong impact on Arctic cirrus formation in the winter of 2019–2020. Via simulations, a detailed insight into the potential of wildfire smoke to influence Arctic cirrus formation as a function of observed meteorological and environmental conditions (temperature, relative humidity, large-scale and gravity-wave-induced lofting conditions, and ice-nucleating particle (INP) concentration) is provided. Lidar-derived values of the INP concentration serve as input, and ice crystal number concentration (ICNC) values retrieved from combined lidar–radar observations are used for comparison with the simulation results. The simulations show that the observed smoke pollution levels in the upper troposphere were high enough to trigger strong ice nucleation. The simulations also corroborate the hypothesis stated in Part 1 (Ansmann et al., 2025): the persistent smoke layer, continuously observed over the central Arctic during the winter half year 2019–2020, was able to widely suppress homogeneous freezing so that the smoke aerosol most probably controlled cirrus formation and properties. The observations suggest that the INP reservoir was continuously refilled from the lower stratosphere. Furthermore, the simulations confirm that the observed high ice saturation ratios of 1.3–1.5 over the North Pole region at cirrus tops (with top temperatures of −60 to −75 °C) point to inefficient INPs, as expected when wildfire smoke particles (organic particles) serve as INPs. Finally, the simulations revealed that ice nucleation in widespread and frequently occurring shallow updrafts (with low amplitudes) seems to be responsible for the observed low ICNC values of typically 1–50 crystals L−1 in the Arctic cirrus virga.

Highlighting the Impact of Anthropogenic OCS Emissions on the Stratospheric Sulfur Budget With In Situ Observations

AbstractCarbonyl sulfide (OCS) is an important atmospheric sulfur species that plays a dominant role in the formation of (nonvolcanic) stratospheric sulfate aerosol in the middle stratosphere. Major uncertainties in surface sources and sinks and inconsistent model representation of vertical transport limit understanding of OCS distribution, particularly in the sparsely sampled upper atmosphere. During the 2022 Asian Summer Monsoon Chemical and CLimate Impact Project (ACCLIP) campaign, in situ measurements of OCS in the Upper Troposphere and Lower Stratosphere (UTLS) at the eastern edge of the Asian summer monsoon anticyclone (ASM), showed significant OCS enhancements (>750 ppt) near the tropopause from convectively influenced air parcels. Here, we compare these novel Asian UTLS measurements with long‐term satellite observations and regional measurements to broaden understanding of OCS trends and its transport by the ASM. Trajectory analysis identifies northern China as the main source region for deep convective lofting of OCS‐enriched parcels and demonstrates ASM entrainment in the UTLS, allowing evaluation of global model predictions for OCS's stratospheric influence. The ACCLIP data set provides vital in situ validation of limited vertically resolved OCS data in a region of significant anthropogenic emissions, which serves to enhance our understanding of the global sulfur budget.

Spatial Structure Functions of Horizontal Winds in the Upper Troposphere and Lower Stratosphere Using Taylor's Hypothesis Over MAARSY (69.30°N, 16.04°E)

AbstractTaylor's hypothesis is traditionally invoked to infer the spatial behavior of flow statistics when its measurements are limited to time series on fixed positions. Here, we evaluate the hypothesis for the estimation of second‐order structure functions in the upper troposphere and lower stratosphere, using 4 years of horizontal wind measurements from the Middle Atmosphere Alomar Radar System, in Northern Norway. Global and local advection velocities are used for the time‐to‐space conversion. We compare with those estimated using wind climatologies from aircraft observations, finding a good agreement for separations between approximately 10 and 1,000 km at 10.5 km altitude. This result enables us to test the 2D turbulence model of a combined energy and enstrophy subrange. It is shown that the spectral energy flux has minima at fixed heights. In contrast, the spectral enstrophy flux steadily decreases with altitude. Both features are consistent with previous modeling and observational studies.

Improving the QBO Forcing by Resolved Waves With Vertical Grid Refinement in E3SMv2

AbstractThe quasi‐biennial oscillation (QBO) is the dominate mode of variability in the tropical stratosphere and plays an important role in stratospheric dynamics and chemistry. The QBO is notably deficient in many climate models, including the Energy Exascale Earth System Model (E3SM) developed by the US Department of Energy. In this work, we refine the lower stratospheric vertical grid spacing from roughly 1 km to 500 m to facilitate more realistic equatorial wave activity in the lower stratosphere in E3SM version 2. The refinement results in a simulated QBO with a reasonable amplitude and easterly‐westerly transition in both directions, but still has a longer period than observed, slower easterly downward propagation speed, and shallower vertical depth. Similar refinement in the multi‐scale modeling framework configuration of E3SM yields similar improvements. By analyzing the forcing contributions from different wave types, we find that most of the QBO forcing still comes from parameterized gravity wave drag from convection. The improved QBO forcing contributions from resolved waves, especially equatorial Kelvin waves and resolved small scale waves, can be attributed to the grid refinement.

Viscosity and Phase State of Wildfire Smoke Particles in the Stratosphere from Pyrocumulonimbus Events: An Initial Assessment.

Understanding the viscosity and phase state of biomass-burning organic aerosol (BBOA) from wildfires and pyrocumulonimbus (pyroCb) events in the stratosphere is critical for predicting their role in stratospheric multiphase chemistry and ozone depletion. However, the viscosity and phase state of BBOA under stratospheric conditions, including interactions with sulfuric acid (H2SO4), remain largely unquantified. In this study, we combine laboratory data with a thermodynamic model to predict the viscosity and phase state of BBOA under stratospheric conditions. Our results suggest that BBOA with a H2SO4-to-BBOA mass ratio of 0.37─an estimated upper limit for pyroCb smoke in the lower stratosphere after two months of aging─is highly viscous and frequently exists in a glassy state. Even at a higher H2SO4-to-BBOA mass ratio of 0.79─an estimated upper limit after nine months of aging─BBOA can still transition to a glassy state under certain stratospheric conditions. In the glassy state, bulk reactions are suppressed, and multiphase chemistry may be limited to the particle surfaces. We also highlight key areas for future research needed to better constrain the viscosity and phase state of BBOA in the stratosphere and its subsequent impact on ozone.

Age of air from ACE-FTS measurements of sulfur hexafluoride

Abstract. Climate models predict that the Brewer–Dobson circulation (BDC) will accelerate due to tropospheric warming, leading to a redistribution of trace gases and, consequently, to a change of the radiative properties of the atmosphere. Changes in the BDC are diagnosed by the so-called “age of air”, that is, the time since air in the stratosphere exited the troposphere. These changes can be derived from a long-term observation-based record of long-lived trace gases with increasing concentration in the troposphere, such as sulfur hexafluoride (SF6). The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) provides the longest available continuous time series of vertically resolved SF6 measurements, spanning 2004 to the present. In this study, a new age-of-air product is derived from the ACE-FTS SF6 dataset. The ACE-FTS product is in good agreement with other observation-based age-of-air datasets and shows the expected global distribution of age-of-air values. Age of air from a chemistry–climate model is evaluated, and the linear trend of the observation-based age of air is calculated in 12 regions within the lower stratospheric midlatitudes (14–20 km, 40–70°) in each hemisphere. In 8 of 12 regions, there was not a statistically significant trend. The trends in the other regions, specifically 50–60 and 60–70° S at 17–20 km and 40–50° N at 14–17 and 17–20 km, are negative and significant to 2 standard deviations. This is therefore the first observation-based age-of-air trend study to suggest an acceleration of the shallow branch of the BDC, which transports air poleward in the lower stratosphere, in regions within both hemispheres.

Transport by Asian Summer Monsoon Convection to the Upper Troposphere and Lower Stratosphere During ACCLIP (2022)

AbstractThe Asian Summer Monsoon (ASM) has garnered attention in recent years for its impacts on the composition of the upper troposphere and lower stratosphere (UTLS) via deep convection. A recent observational effort into this mechanism, the Asian Summer Monsoon Chemical and CLimate Impact Project (ACCLIP), sampled the composition of the ASM UTLS over the northwestern Pacific region during boreal summer 2022 using two airborne platforms. In this work, we integrate Lagrangian trajectory modeling with convective cloud top observations to diagnose ASM convective transport which contributed to ACCLIP airborne observations. This diagnostic is applied to explore the properties of convective transport associated with prominent ASM sub‐systems, revealing that for species ranging in lifetime from days to months, transport from convection along the East Asia Subtropical Front was generally associated with more UTLS pollutants than transport from convection over South Asia. The convective transport diagnostic is used to isolate three convective transport events over eastern Asia which had distinct chemical tracer relationship behaviors, indicating the different economical behaviors of the contributing source regions. One of these transport events is explored in greater detail, where a polluted air mass was sampled from convection over the Northeast China Plain which may have been high enough in altitude to impact the composition of the stratosphere. Overall, the presented diagnosis of convective transport contribution to ACCLIP airborne sampling indicates a key scientific success of the campaign and enables process studies of the climate interactions from the two ASM sub‐systems.

How South Asian Thunderstorm‐Driven Transport Affects the Atmospheric Composition Over the Tibetan Plateau and Stratosphere

AbstractThe Tibetan Plateau (TP) is an important gateway for tropospheric substances enter the stratosphere. South Asia, especially its northwesternmost part, is emerging as a global hotspot for thunderstorms and lightning, driven by dynamic interactions between the orography of the TP and the South Asian Summer Monsoon (SASM). This study used TRMM satellite observations from 1998 to 2013, combined with ERA‐5 reanalysis data and the HYSPLIT trajectory model, to comprehensively investigate how thunderstorms in the region impact the atmospheric composition over the TP. The findings reveal that thunderstorms in the region predominantly occur during the SASM. Spatially, these thunderstorms are concentrated along the southern Himalayan front, especially in the westernmost indentation between the TP and the Iranian Plateau, an area also characterized by heavy anthropogenic pollution. By employing the HYSPLIT model to trace transport pathways associated with the thunderstorm, the study demonstrates a clear convergence of pollutants from the South Asia boundary layer into thunderclouds. Furthermore, three principal transport pathways were identified for substances originating from the tops of thunderstorms entering the TP. These pathways are closely linked to the tropospheric westerlies, the anticyclonic circulation of the South Asian High, and processes penetrating the tropopause, accounting for approximately 58%, 33%, and 9% of thunderstorms, respectively. Notably, the impact of these thunderstorm‐driven transport processes on the TP and even the lower stratosphere is expected to intensify as thunderstorms become more frequent and pollution levels rise in South Asia due to global warming and local social development.

Impact of Solar Proton Events on the Stratospheric Polar Vortex in the Northern Hemisphere: A Quantitative Analysis

AbstractThe stratospheric polar vortex (SPV) profoundly affects northern hemisphere weather and climate, with its dynamics influenced by terrestrial and solar factors. Despite established terrestrial influences, the quantitative effects of solar energetic particles have not yet been fully understood. This study presents a quantitative analysis of 27 intense solar proton events (SPEs) from 1986 to 2020, revealing a significant correlation between the integrated flux of SPEs and enhanced SPV wind speeds across altitudes. Notably, the wind speed enhancements, ranging from 1.8 m/s (15.1%) at 100 hPa to 3.0 m/s (7.3%) at 1 hPa, demonstrate an altitude‐dependent pattern, with the greatest impacts of 5.8 m/s (19.1%) at 5 hPa. A partial correlation analysis identifies SPEs as the dominant driver of SPV enhancement in the middle and lower stratosphere, while ultraviolet radiation dominates at the stratopause. We propose a mechanism involving the amplification of the meridional temperature gradient due to differential ozone responses, thereby linking solar activity to the modulation of the SPV. These findings enhance our understanding of solar‐terrestrial interactions and their implications for climate modeling.

Impacts of Atmospheric Stratification on the Behaviors of Stratospheric Weak Polar Vortex Events

Abstract Based on a highly idealized wave–mean flow interaction model, where the planetary waves are excited by the specified bottom-boundary geopotential perturbation, this study investigates the modulation of prescribed atmospheric stratification N2 conditions on the stratospheric weak polar vortex (WPV) events’ characteristics and the underlying mechanism. In the vertically uniform N2 experiments, strong N2 and the consequent large refractive index squared of planetary waves preceding WPVs facilitate enhanced vertical wave propagation. The resultant WPVs are more intense because a significant convergence of wave activity flux in the upper stratosphere amplifies polar stratospheric warming and drastically collapses the polar night jet. The WPVs are also more persistent because the diabatic cooling process requires a longer period to cool the polar stratosphere and reestablish the polar vortex. In contrast, weak N2 facilitates WPVs that are less intense and persistent. The difference in the vertical planetary wave propagation explains how N2 shapes contrasting WPV characteristics. Considering the vertical wave propagation depends not only on N2 but also on the mean flow, the mean flow is further fixed to isolate the effects of N2. The results remain the same, highlighting the crucial role of N2 in modulating the WPV characteristics. Further experiments with vertically changing N2 suggest that N2 in the lower stratosphere is more efficient in modulating the WPV characteristics.

On the estimation of stratospheric age of air from correlations of multiple trace gases

Abstract. The stratospheric circulation is an important element in the climate system, but observational constraints are prone to significant uncertainties due to the low circulation velocities and uncertainties in available trace gas measurements. Here, we propose a method to calculate mean age of air as a measure of the circulation from observations of multiple trace gas species which are reliably measurable by satellite instruments, like trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), chlorodifluoromethane (HCFC-22), methane (CH4), nitrous oxide (N2O), and sulfur hexafluoride (SF6), and we show that this method works well in most of the lower stratosphere up to a height of about 25 km. The method is based on the compact correlations of these gases with mean age. Methodological uncertainties include effects of atmospheric variability, non-compactness of the correlation, and measurement related effects inherent for satellite instruments. The multi-species age calculation method is evaluated in a model environment and compared against the actual model age from an idealized clock tracer. We show that combination of the six chosen species reduces the resulting uncertainty of derived mean age to below 0.3 years throughout most regions in the lower stratosphere. Even small-scale, seasonal features in the global age distribution can be reliably diagnosed. The new correlation method is further applied to trace gas measurements with the balloon-borne Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA-B) instrument. The corresponding deduced mean age profiles agree reliably with SF6-based mean age below about 22 km and show significantly lower uncertainty ranges. Comparison between observation-based and model-simulated mean ages indicates a slow-biased circulation in the ERA5 reanalysis. Overall, the proposed mean age calculation method shows promise to substantially reduce the uncertainty in mean age estimates from satellite trace gas observations.

First measurement of small-scale turbulence over long horizontal paths in the lower stratosphere and study of non-Kolmogorov turbulence characteristic parameters

First measurement of small-scale turbulence over long horizontal paths in the lower stratosphere and study of non-Kolmogorov turbulence characteristic parameters

The Impact of Tropical Sea Surface Temperature on the Arctic Stratospheric Polar Vortex Trend

ABSTRACTThe changes in the Arctic stratospheric polar vortex are influenced by various factors and exert impacts on both the weather and climate of the troposphere and the surface. In this study, we analysed the trends of the stratospheric polar vortex using the self‐organising map (SOM) method. There is a decreasing trend in the occurrence of strong polar vortices, while there is an increasing trend in the occurrence of weak polar vortices. The analysis revealed that nine nodes (3 × 3) of SOMs can explain approximately one‐third (the trend contribution ratio is 33.4%) of the significant increase in the geopotential height field, in which two nodes (Nodes 3 and 7) amount to approximately three‐quarters (25.23%) of the total contribution (33.4%). Significantly positive sea surface temperature (SST) anomalies in the tropical western Pacific and the southwestern Pacific Ocean associated with Node 3 enhanced convective activity in these areas, resulting in negative Rossby wave sources (RWS) and divergent winds, triggering a Rossby wave train. This wave train generates positive geopotential height anomalies over the Arctic Ocean in the stratosphere, which helps weaken the Arctic polar vortex. A wave train excited by suppressed convective activity in the tropical West Pacific and South China Sea related to Node 7 propagates northeastward along a similar path to middle and high latitudes. However, this wave train induces geopotential height anomalies opposite in sign over the Arctic Ocean, which favours the strengthening of the polar vortex. The EP flux in the high‐latitude lower stratosphere associated with the two above wave trains can explain the Arctic polar vortex anomalies. Our results show that the influence of SST in the warm pool region on the stratospheric polar vortex is greater than in other ocean regions.

The Impact of 2022 Hunga Tonga‐Hunga Ha'apai (Hunga) Eruption on Stratospheric Circulation and Climate

AbstractThe Hunga Tonga‐Hunga Ha'apai (Hunga) volcanic eruption in January 2022 injected a substantial amount of water vapor and a moderate amount of SO2 into the stratosphere. Both satellite observations in 2022 and subsequent chemistry‐climate model simulations forced by realistic Hunga perturbations reveal large‐scale cooling in the Southern Hemisphere (SH) tropical to subtropical stratosphere following the Hunga eruption. This study analyzes the drivers of this cooling, including the distinctive role of anomalies in water vapor, ozone, and sulfate aerosol concentration on the simulated climate response to the Hunga volcanic forcing, based on climate simulations with prescribed chemistry/aerosol. Simulated circulation and temperature anomalies based on specified‐chemistry simulations show good agreement with previous coupled‐chemistry simulations and indicate that each forcing of ozone, water vapor, and sulfate aerosol from the Hunga volcanic eruption contributed to the circulation and temperature anomalies in the SH stratosphere. Our results also suggest that (a) the large‐scale stratospheric cooling during the austral winter was mainly induced by changes in dynamical processes, not by radiative processes, and that (b) the radiative feedback from negative ozone anomalies contributed to the prolonged cold temperature anomalies in the lower stratosphere (∼70 hPa level) and hence to long lasting cold conditions of the polar vortex.

Ozone trends in homogenized Umkehr, ozonesonde, and COH overpass records

Abstract. This study presents an updated evaluation of stratospheric ozone profile trends at Arosa/Davos/Hohenpeißenberg, Switzerland/Germany; Observatory de Haute-Provence (OHP), France; Boulder, Colorado, Mauna Loa Observatory (MLO) and Hilo, Hawaii; and Lauder, Aotearoa / New Zealand, with a focus on the ozone recovery period post-2000. Trends are derived using vertical ozone profiles from NOAA's Dobson network via the Umkehr method (with a recent new homogenization), ozonesondes, and the NOAA COHesive Solar Backscatter Ultraviolet Instrument (SBUV)/Ozone Mapping and Profiler Suite (OMPS) satellite-based record (COH) sampled to match the geographical coordinates of the ground-based stations used in this study. Analyses of long-term changes in stratospheric ozone time series were performed using the updated version (0.8.0) of the Long-term Ozone Trends and Uncertainties in the Stratosphere (LOTUS) independent linear trend (ILT) regression model. This study finds consistency between the trends derived from the different observational records, which is a key factor to the understanding of the recovery of the ozone layer after the implementation of the Montreal Protocol and its amendments that control ozone-depleting substance production and release into the atmosphere. The northern hemispheric Umkehr records of Arosa/Davos, OHP, and MLO all show positive trends in the mid- to upper stratosphere, with trends peaking at ∼ +2 % per decade. Although the upper-stratospheric ozone trends derived from COH satellite records are more positive than those detected by the Umkehr system, the agreement is within the 2 times the standard error uncertainty. Umkehr trends in the upper stratosphere at Boulder and Lauder are positive but not statistically significant, while COH trends are larger and statistically significant (within 2 times the standard error uncertainty). In the lower stratosphere, trends derived from Umkehr and ozonesonde records are mostly negative (except for positive ozonesonde trends at OHP); however, the uncertainties are quite large. Additional dynamical proxies were investigated in the LOTUS model at five ground-based sites. The use of additional proxies did not significantly change trends, but the equivalent latitude reduced the uncertainty in the Umkehr and COH trends in the upper stratosphere and at higher latitudes. In lower layers, additional predictors (tropopause pressure for all stations; two extra components of Quasi-Biennial Oscillation at MLO; Arctic Oscillation at Arosa/Davos, OHP, and MLO) improve the model fit and reduce trend uncertainties as seen by Umkehr and sonde.

Machine learning for improvement of upper-tropospheric relative humidity in ERA5 weather model data

Abstract. Knowledge of humidity in the upper troposphere and lower stratosphere (UTLS) is of special interest due to its importance for cirrus cloud formation and its climate impact. However, the UTLS water vapor distribution in current weather models is subject to large uncertainties. Here, we develop a dynamic-based humidity correction method using an artificial neural network (ANN) to improve the relative humidity over ice (RHi) in ECMWF numerical weather predictions. The model is trained with time-dependent thermodynamic and dynamical variables from ECMWF ERA5 and humidity measurements from the In-service Aircraft for a Global Observing System (IAGOS). Previous and current atmospheric variables within ±2 ERA5 pressure layers around the IAGOS flight altitude are used for ANN training. RHi, temperature, and geopotential exhibit the highest impact on ANN results, while other dynamical variables are of low to moderate or high importance. The ANN shows excellent performance, and the predicted RHi in the UT has a mean absolute error (MAE) of 5.7 % and a coefficient of determination (R2) of 0.95, which is significantly improved compared to ERA5 RHi (MAE of 15.8 %; R2 of 0.66). The ANN model also improves the prediction skill for all-sky UT/LS and cloudy UTLS and removes the peak at RHi = 100 %. The contrail predictions are in better agreement with Meteosat Second Generation (MSG) observations of ice optical thickness than the results without humidity correction for a contrail cirrus scene over the Atlantic. The ANN method can be applied to other weather models to improve humidity predictions and to support aviation and climate research applications.

Student Hands-on Atmospheric Discovery during an Eclipse (SHADE) over Texas

Abstract On 8 April 2024, a total solar eclipse overpassed Texas in the southern portion of the United States. To monitor the impact of the total solar eclipse, a group of students from Texas A&M University–Corpus Christi developed two weather balloon payloads and six ground-based instrument packages using microcontrollers and low-cost sensors. These instrument packages were deployed to six different sites spanning nearly 600 km along the total eclipse path from the Mexican border to North Texas. During the total eclipse, air temperature decreased, and relative humidity increased consistently at all six stations due to the reduction in sensible heating. The dewpoint temperatures decreased at the near surface at all sites likely due to the reduction in evaporation. Five of the six ground stations observed a slight dampening of the wind speed, and two of the six stations recorded significant counterclockwise wind shifts. No consistent pattern was observed in the surface vertical electric field at the six ground stations. The two balloon payloads captured the damping of the visible and ultraviolet (UV) radiation in the upper troposphere and lower stratosphere throughout the event. Though a slight decrease in both temperature and ozone in the lower stratosphere was observed after the totality, it is difficult to determine the impact from the eclipse on the ozone mixing ratio and dynamics in the lower stratosphere from only a few vertical profiles. For the students who participated, this field campaign has provided invaluable experiences in instrumentation, fieldwork, and data collection.

Dynamic Impact of the Southern Annular Mode on the Antarctic Ozone Hole Area

This study investigates the impact of dynamic variability of the Southern Hemisphere (SH) polar middle atmosphere on the ozone hole area. We analyze the influence of the southern annular mode (SAM) and planetary waves (PWs) on ozone depletion from 19 years (2005–2023) of aura microwave limb sounder (MLS) geopotential height (GPH) measurements. We employ empirical orthogonal function (EOF) analysis to decompose the GPH variability into distinct spatial patterns. EOF analysis reveals a strong relationship between the first EOF (representing the SAM) and the Antarctic ozone hole area (γ = 0.91). A significant negative lag correlation between the August principal component of the second EOF (PC2) and the September SAM index (γ = −0.76) suggests that lower stratospheric wave activity in August can precondition the polar vortex strength in September. The minor sudden stratospheric warming (SSW) event in 2019 is an example of how strong wave activity can disrupt the polar vortex, leading to significant temperature anomalies and reduced ozone depletion. The coupling of PWs is evident in the lag correlation analysis between different altitudes. A “bottom-up” propagation of PWs from the lower stratosphere to the mesosphere and a potential “top-down” influence from the mesosphere to the lower stratosphere are observed with time lags of 21–30 days. These findings highlight the complex dynamics of PW propagation and their potential impact on the SAM and ozone layer. Further analysis of these correlations could improve one-month lead predictions of the SAM and the ozone hole area.