Session AS1.29

AS1.29 | Dynamics and chemical composition of the stratosphere

Dynamics and chemical composition of the stratosphere

Convener: Mohamadou DialloECSECS | Co-conveners: Thomas Reichler, Gloria Manney, Farahnaz Khosrawi, Masatomo Fujiwara, Bo Christiansen, Gabriel ChiodoECSECS

Orals

| Tue, 16 Apr, 08:30–12:25 (CEST)

Room M1

Posters on site

| Attendance Mon, 15 Apr, 10:45–12:30 (CEST) | Display Mon, 15 Apr, 08:30–12:30

Hall X5

Dynamics, transport processes and chemical composition in the stratosphere and and the related feedbacks are inextricably linked. Changes in any of these aspects are in turn linked to changes in tropospheric circulation, climate, and weather events via two-way coupling. Such changes can be driven or triggered by a variety of natural (e.g., ENSO, QBO, SSWs, solar and volcanic activity, wildfires) and anthropogenic (emissions of radiatively or chemically active gases) processes. Better understanding of these processes and their consequences is important to improving understanding and prediction of changes in weather, climate, and air quality, including those related to extreme weather events. We welcome abstracts based on observational and modelling studies that explore dynamical, chemical, and transport processes in the stratosphere and their links to surface conditions on all time scales. Combined use of modelling and data analysis is particularly encouraged, including climate model and reanalysis comparisons with existing satellite and ground-based datasets, plans for new missions or model / data assimilation development, and studies highlighting new analytical approaches, e.g., based on machine learning, for evaluating and linking stratospheric processes with surface weather and climate.

Orals: Tue, 16 Apr | Room M1

Chairpersons: Mohamadou Diallo, Thomas Reichler, Gabriel Chiodo

08:30–08:35

5-minute convener introduction

Stratospheric dynamical and chemical feedback

08:35–08:55

EGU24-3155

solicited

Highlight

On-site presentation

Emerging importance of chemistry-climate coupling on weather to climate timescales

Michaela I. Hegglin

08:55–09:05

EGU24-8884

ECS

solicited

Highlight

On-site presentation

The Role of the Stratosphere in Driving Uncertainties in the Southern Hemisphere Future Climate

Julia Mindlin, Carolina S. Vera, Theodore G. Shepherd, and Marisol Osman

The strength and latitudinal position of the extratropical eddy-driven jet (EDJ) in the Southern Hemisphere (SH) winter and summer is naturally forced by the conditions of the tropical oceans and by the variability of the SH stratospheric polar vortex (SPV). Uncertainty in the responses of these remote drivers (RDs) of extratropical circulation to anthropogenic forcing leads to uncertainty in the future strength and latitude of the EDJ. In turn, these changes in tropospheric circulation can lead to changes at the regional scale. During this century, the combined effect of ozone recovery and the increase in greenhouse gases (GHGs) will influence the SPV. Therefore, understanding the ‘tug-of-war’ between these two anthropogenic forcings is crucial to understand future projections. Moreover, the influences of the stratosphere will be combined with the influences of forced changes in the tropics. This complex interplay between RDs and the magnitude of each RD’s response to anthropogenic forcings differs among Global Climate Models (GCMs), which leads to different responses of the EDJ and regional climate. In this work we analyze an ensemble of CMIP6 models to study the role of forced responses in the SPV in driving changes in climate projections, and how the influence of the stratospheric changes combines with the influence of the changes in a small set of tropical RDs. In particular, we find that a strengthening of the SPV leads to a strengthening and small poleward shift of the EDJ in winter, and that a delay in the SPV breakdown date leads to a strong poleward shift of the EDJ in summer. The evolution of the summer circulation response in CMIP6 models during the twenty-first century can be explained from the combined effect of ozone recovery and GHG increase. At the regional scale, in winter, a strengthening of the SPV leads to drying in Southeastern South America and wetting in Tierra del Fuego, in the south of South America, while in summer, a SPV breakdown delay leads to wetting in the west coast of all three large extratropical continental sectors and the coasts of Antarctica. Finally, we develop storylines of future circulation and precipitation changes in both summer and winter which help understand the relative role of the SPV among other dynamical drivers of change in the SH.

How to cite: Mindlin, J., Vera, C. S., Shepherd, T. G., and Osman, M.: The Role of the Stratosphere in Driving Uncertainties in the Southern Hemisphere Future Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8884, https://doi.org/10.5194/egusphere-egu24-8884, 2024.

09:05–09:15

EGU24-9249

ECS

Highlight

On-site presentation

Impact of the 2022 Hunga Tonga Volcano on Global Middle Atmosphere Water Vapour and Climate Implications

Alistair Bell, Gunter Stober, Klemens Hocke, and Axel Murk

The 2022 Hunga Tonga–Hunga Haʻapai volcano eruption was a major global event, injecting a significant volume of water vapour into the stratosphere and contributing to an estimated 10% increase in global stratospheric water vapour. Due to the fact that water vapour is the most powerful greenhouse gas not directly controlled by anthropogenic activities, this has implications on the radiative heating at the surface and thus surface temperatures.

Due to the elevated location of the water vapour anomaly, obtaining measurements of the mixing ratio of the anomaly is challenging. Employing two microwave radiometers, operated by the Institute of Applied Physics (IAP) in Bern, Switzerland, profiles of water vapour mixing ratio are presented at two locations: Switzerland and Svalbard. Analysis of data from these points, dating back to 2010, reveals the anomaly's characteristics and its influence on surface radiative heating.

Our findings are contextualized with additional data from satellite observations, in-situ instruments, and other ground-based microwave radiometers. This comprehensive approach allows us to explore the wider implications of the Hunga Tonga eruption on the climate, particularly in relation to 2023, a year noted as the hottest on record.

How to cite: Bell, A., Stober, G., Hocke, K., and Murk, A.: Impact of the 2022 Hunga Tonga Volcano on Global Middle Atmosphere Water Vapour and Climate Implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9249, https://doi.org/10.5194/egusphere-egu24-9249, 2024.

09:15–09:25

EGU24-13753

ECS

Highlight

On-site presentation

The NOAA Balloon Baseline Stratospheric Aerosol Profiles (B2SAP) – In situ insight on the stratospheric aerosol layer

Alexandre Baron, Elizabeth Asher, Katie Smith, and Troy Thornberry and the B2SAP extended Team

Stratospheric aerosols play a crucial role in the climate system, but uncertainties persist in understanding the chemical, dynamical, and microphysical processes governing their distribution and variability. The chemical and radiative impacts of stratospheric aerosols hinge on particle size distribution. However, models exhibit significant variations in how they parameterize aerosol microphysical processes and simulate size distributions, leading to divergent predictions of the time evolution of radiative impacts from stratospheric aerosol perturbation events. To refine models for assessing the effects of potential climate intervention strategies, systematic measurements are crucial. In pursuit of this understanding, the Baseline Balloon Stratospheric Aerosol Profiles (B²SAP) project utilizes compact, lightweight payloads carried by meteorological balloons. These payloads measure aerosol number density and size distributions, along with water vapor, ozone, and meteorological data from the surface to the middle stratosphere. The long-term goal of the B²SAP project is to generate climatologies of aerosol number and size distributions up to the middle stratosphere at latitudinally distributed measurement sites. Since March 2019, B²SAP payloads have been launched from Boulder, CO, USA (40°N) once to twice per month and four to six times per year from Lauder, NZ (45°S). Starting in 2022, two tropical sites were added to this evanescent network with quarterly launches: Hilo, HI, USA (20°N) and Reunion Island, FR (20°S). These measurements provide a new record of in situ observations allowing to characterize the natural stratospheric aerosol burden, its variability, and responses to perturbations, providing essential data for refining models and aiding in the validation of satellite-based estimates. In this context, we will present a subset of this growing database, emphasizing the discussion on the stratospheric aerosol layers in the North hemisphere and South hemisphere (SH) mid-latitudes. Perturbations recorded in the SH after the Australian New Year super pyroCb outbreak in 2020 will also be investigated.

How to cite: Baron, A., Asher, E., Smith, K., and Thornberry, T. and the B2SAP extended Team: The NOAA Balloon Baseline Stratospheric Aerosol Profiles (B2SAP) – In situ insight on the stratospheric aerosol layer , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13753, https://doi.org/10.5194/egusphere-egu24-13753, 2024.

09:25–09:35

EGU24-1341

ECS

On-site presentation

The Key Role of the Vertical Structure of the Stratospheric Quasi-Biennial Oscillation in the Variations of Asian Precipitation in Summer

(withdrawn)

Fuhai Luo, Jiali Luo, Fei Xie, Wenshou Tian, Yihang Hu, Leiye Yuan, Ruhua Zhang, and Tao Wang

09:35–09:45

EGU24-8035

On-site presentation

Multi-decadal variability controls short-termstratospheric water vapor trends

Mengchu Tao, Paul Konopka, Jonathon S. Wright, Yi Liu, Jianchun Bian, Sean M. Davis, Yue Jia, and Felix Ploeger

Stratospheric Dynamics

09:45–09:55

EGU24-3026

Virtual presentation

Downward coupling mechanism of Sudden Stratospheric Warming: A Mass Flux Perspective

Seok-Woo Son and Dong-Chan Hong

Sudden Stratospheric Warming (SSW) is an important source of subseasonal-toseasonal predictability due to its significant and long-lasting impacts on surface climate. However, the mechanism of its downward coupling has not yet been fully elucidated. In this study, we investigate the downward coupling mechanism of SSW in terms of mass redistribution. Out of the 65-year dataset of the Japanese 55-year Reanalysis (JRA-55), 40 SSW events are identified. Their composite shows a significant increase of tropospheric geopotential and pressure anomalies over the Arctic (60-90°N) after the onset with a prominent surface amplification. The decomposition of tropospheric anomalies into surface pressure and air temperature components reveals that the downward coupling mainly results from surface pressure change. It is further found that surface pressure change during the SSW onset is primarily caused by the poleward mass flux near the tropopause, which is mainly driven by momentum flux change in the upper troposphere. This momentum flux change is consistent with the poleward propagation of wave, and it is may associated with the warm temperature anomalies during the SSW. These findings provide a new insight on SSW downward coupling and surface amplification.

How to cite: Son, S.-W. and Hong, D.-C.: Downward coupling mechanism of Sudden Stratospheric Warming: A Mass Flux Perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3026, https://doi.org/10.5194/egusphere-egu24-3026, 2024.

09:55–10:05

EGU24-13281

On-site presentation

Quantifying the role of the stratosphere in upward wave propagation during stratospheric polar vortex disturbances: an SNAPSI Working Group 4 analysis

Blanca Ayarzagüena, Amy H. Butler, Chaim Garfinkel, Peter Hitchcock, Hilla Afargan-Gerstman, Thomas Birner, Natalia Calvo, Álvaro de la Cámara, Nahuel Gómez, Martin Jucker, Gebrand Koren, Zachary Lawrence, Gloria Manney, Wuhan Ning, Marisol Osman, Philip Rupp, Masakazu Taguchi, Wolfgang Wicker, and Zheng Wu and the SNAPSI WG4

Sudden stratospheric warmings (SSWs) are the most dramatic wintertime stratospheric phenomena. They are preceded by a sustained wave dissipation in the stratosphere that leads to the deceleration of the polar vortex. The signal from SSWs then typically propagates downward reaching the troposphere and inducing a negative phase of the Annular Mode that may persist several weeks up to two months. Incorporating then stratospheric information in subseasonal to seasonal (S2S) forecast systems has been shown to improve the skill of S2S predictions for surface climate. However, on average, present S2S forecast systems can only predict SSWs around two weeks before the onset of the event. A suggested strategy to increase their predictability is to improve the representation of triggering mechanisms of SSWs. However, while there is a consensus on the relevance of the wave activity for that, the origin of the rapid enhancement of stratospheric wave activity prior to SSWs is not sufficiently understood.

The aim of this study is two-fold: to assess the ability of forecast systems to reproduce the stratospheric wave amplification during SSWs and to quantify the role of the stratosphere in this enhanced upward wave propagation. To do so, we analyze the triggering mechanisms of three different SSWs, the boreal SSWs of 2018 and 2019 and the austral minor SSW of 2019, by means of SNAPSI (Stratospheric Nudging And Predictable Surface Impacts) sets of forecast ensembles. These ensembles include free-evolving atmospheric runs and nudged simulations where the zonally-symmetric stratospheric state is nudged to either observations of a certain SSW or a climatological state. Our results show that models struggle to predict the SSW of 2018, as they are not able to capture the strong enhancement of wavenumber-2 wave activity around one week before the event. In contrast, most ensemble members of all models are able to simulate both SSWs of 2019, but with some common issues such as an early timing for the NH event and a weaker deceleration of the vortex in the case of the SH SSW. In the three cases, capturing both the tropospheric precursors and the interactions of waves with the stratospheric flow are revealed to be crucial for the occurrence of the phenomena. However, the relative role of each contribution is different depending on the individual event. This is a contribution of the Working Group 4 of the SNAPSI initiative.

How to cite: Ayarzagüena, B., Butler, A. H., Garfinkel, C., Hitchcock, P., Afargan-Gerstman, H., Birner, T., Calvo, N., de la Cámara, Á., Gómez, N., Jucker, M., Koren, G., Lawrence, Z., Manney, G., Ning, W., Osman, M., Rupp, P., Taguchi, M., Wicker, W., and Wu, Z. and the SNAPSI WG4: Quantifying the role of the stratosphere in upward wave propagation during stratospheric polar vortex disturbances: an SNAPSI Working Group 4 analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13281, https://doi.org/10.5194/egusphere-egu24-13281, 2024.

Discussion Post a comment

10:05–10:15

EGU24-4343

ECS

Virtual presentation

Exploring the role of tropospheric stationary waves for the North Pacific response to SSWs

Rachel Wai-Ying Wu, Hilla Afargan-Gerstman, and Daniela I.V. Domeisen

Stratospheric variability can have a significant impact on surface weather extremes in winter, in particular during stratospheric extreme events, so-called sudden stratospheric warming (SSW) events. The stratospheric downward impact has been shown to be communicated by both planetary-scale and synoptic-scale waves, but their relative roles and interactions are not fully understood. Since there is a strong average response to stratospheric forcing over the North Atlantic but a weak response over the North Pacific, studies of SSW downward impact generally focus on the North Atlantic, where the synoptic eddy-feedback plays a strong role. We here examine the relative roles of planetary-scale waves for the North Pacific after SSW events. By examining the case-by-case response over the North Pacific following SSW onset using ERA5 reanalysis, we identify differences between events in terms of their interactions between the wave anomalies induced by the stratosphere and the tropospheric stationary waves. Specifically, the destructive and constructive interference of zonal wavenumber-1 anomalies plays a dominant role in contributing to different responses over the North Pacific, which are associated with an equatorward and a poleward jet shift, respectively. We suggest that SSW events can exhibit opposite responses over the North Pacific, potentially explaining the generally weak response observed in this region when averaging across all SSW events.

How to cite: Wu, R. W.-Y., Afargan-Gerstman, H., and Domeisen, D. I. V.: Exploring the role of tropospheric stationary waves for the North Pacific response to SSWs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4343, https://doi.org/10.5194/egusphere-egu24-4343, 2024.

Coffee break

Chairpersons: Gloria Manney, Farahnaz Khosrawi, Bo Christiansen

10:45–10:55

EGU24-4273

ECS

On-site presentation

Defining Arctic Stratospheric Polar Vortex Intensification Events

Jinlong Huang and Peter Hitchcock

Using the ERA5 reanalysis data, we identify seven easily calculable indices of the strength of theArctic stratospheric vortex: zonal winds at 10 hPa and temperature or height anomalies at 10 , 50, and 100 hPa.We then compare the climatological statistics and meteorological properties of strong and weak events basedon these indices. We particularly consider the sensitivity of the event statistics to the choice of thresholds, theuse of these indices in capturing stratosphere–troposphere coupling, and meteorological conditions relevant tochemical ozone depletion. The frequency, seasonal distribution, and interdecadal variability of strong eventsis more sensitive to threshold or index choice compared to weak events. Composites of polar-cap geopotentialheight anomalies are found to differ significantly based on the choice of index. In particular, height-basedevents reveal a strong and immediate barotropic response near the central date due to surface pressurefluctuations, making it more difficult to regard central dates of height-based events as purely stratosphericin origin. We further characterize the relationship of all indices to conditions relevant to chemical ozonedepletion, finding that temperature-based indices in the lower stratosphere perform best. Finally, we presentfour dynamical benchmarks used to assess and compare the representation of strong events in climate models.Our results highlight the challenges in determining the optimal definition for strong events and emphasizethe implications of different choices, providing valuable insights for guiding future studies in defining strong events.

How to cite: Huang, J. and Hitchcock, P.: Defining Arctic Stratospheric Polar Vortex Intensification Events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4273, https://doi.org/10.5194/egusphere-egu24-4273, 2024.

10:55–11:05

EGU24-5302

ECS

On-site presentation

Towards a direct simulation of a full cycle of the quasi-biennial oscillation in a global storm-resolving model

Henning Franke and Marco Giorgetta

This study presents the very first attempt to directly simulate a full cycle of the quasi-biennial oscillation (QBO) in a global storm-resolving model (GSRM) that explicitly resolves deep convection and gravity waves instead of parameterizing them. Using the ICOsahedral Nonhydrostatic (ICON) model with a horizontal and vertical resolution of about 5 km and 400 m, respectively, we show that a GSRM in the convective gray zone is in principle capable of simulating the basic dynamics that lead to a QBO-like oscillation of the zonal wind in the tropical stratosphere. ICON shows overall good fidelity in simulating the downward propagation of QBO jets in the upper tropical stratosphere, which happens also for the right reasons. In the lower stratosphere, however, ICON does not simulate the downward propagation of the QBO jets to the tropopause, predominantly due to a pronounced lack of planetary-scale wave forcing. As a consequence, the QBO jets degrade with increasing simulation time and lose strength substantially. We show that the lack of planetary-scale wave forcing in the lower stratosphere is caused by a lack of planetary-scale wave momentum fluxes entering the stratosphere, which are about 20%–40% too weak. We attribute this lack of planetary-scale wave momentum flux to a substantial underestimation of the spatio-temporal variability of tropical deep convection in general and convectively coupled equatorial waves in the tropical troposphere in particular. While conventional general circulation models can compensate for a lack in resolved wave forcing by tuning the parameterized gravity wave forcing, GSRMs no longer have this tuning screw, making their QBO more susceptible to being influenced by tropospheric mean state biases. We thus conclude that simulating a realistic spatio-temporal variability of tropical convection is currently the main roadblock towards simulating a reasonable QBO in GSRMs.

How to cite: Franke, H. and Giorgetta, M.: Towards a direct simulation of a full cycle of the quasi-biennial oscillation in a global storm-resolving model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5302, https://doi.org/10.5194/egusphere-egu24-5302, 2024.

11:05–11:15

EGU24-6801

On-site presentation

Arctic Sea Ice Loss, Long-Term Trends in Extratropical Wave Forcing, and the Observed Strengthening of the QBO-MJO Connection

Lon Hood and Charles A. Hoopes

A modulation has been identified of the tropical Madden-Julian oscillation (MJO) by the stratospheric quasi-biennial oscillation (QBO) such that the MJO in boreal winter is ~ 40% stronger and persists ~10 days longer during the easterly QBO phase (QBOE) than during the westerly phase. A proposed mechanism is reductions of tropical lower stratospheric static stability during QBOE caused by (1) the QBO induced meridional circulation; and (2) QBO influences on extratropical wave forcing of the stratospheric residual meridional circulation during early winter. Here, long-term variability of the QBO-MJO connection and associated variability of near-tropopause tropical static stability and extratropical wave forcing are investigated using European Center reanalysis data for the 1959-2021 period. During the most reliable (post-satellite) part of the record beginning in 1979, a strengthening of the QBO-MJO modulation has occurred during a time when tropical static stability in the lowermost stratosphere and uppermost troposphere has been decreasing and extratropical wave forcing in early winter has been increasing. A high inverse correlation (R = -0.87) is obtained during this period between early winter wave forcing anomalies and wintertime tropical lower stratospheric static stability. Regression relationships are used to show that positive trends in early winter wave forcing during this period have likely contributed to decreases in tropical static stability, favoring a stronger QBO-MJO connection. As shown in previous work, increased sea level pressure anomalies over northern Eurasia produced by Arctic sea ice loss may have been a significant source of the observed positive trends in early winter wave forcing.

How to cite: Hood, L. and Hoopes, C. A.: Arctic Sea Ice Loss, Long-Term Trends in Extratropical Wave Forcing, and the Observed Strengthening of the QBO-MJO Connection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6801, https://doi.org/10.5194/egusphere-egu24-6801, 2024.

Discussion Post a comment

11:15–11:25

EGU24-8621

On-site presentation

Extratropical teleconnections in an ensemble of models nudged towards the observed equatorial QBO

Martin Andrews, Neal Butchart, James Anstey, Ewa Bednarz, Dillon Elsbury, Vinay Kumar, Froila Palmeiro, Natasha Trencham, Zhaoyang Chai, Qi Tang, Jinbo Xie, Pu Lin, Francois Lott, Shingo Watanabe, Aleena Jaison, Jeff Knight, Hiroaki Naoe, and Kohei Yoshida

The Quasi-Biennial Oscillation (QBO) is the leading natural model of interannual variability of the zonal mean wind in the equatorial stratosphere, consisting of alternating regions of easterly and westerly zonal wind that descend through the equatorial stratosphere with a mean period of approximately 28 months. Its dominant influence on the dynamical structure of the equatorial stratosphere raises the prospect of teleconnections to the extratropical atmosphere. For example, the QBO has been linked to variability in the Northern Hemisphere winter stratospheric polar vortex, the timing and frequency of sudden stratospheric warmings, the phase of the North Atlantic Oscillation, and the modulation of tropospheric mid-latitude waves in the Pacific region. However, the reproduction of these extratropical teleconnections in free-running models relies upon on a quantitatively realistic internally-generated QBO, and the ability of the model dynamics to respond to this QBO. To isolate the dynamical response, a new experiment protocol, defined by the Atmospheric Processes and their Role in Climate (APARC) Quasi-Biennial Oscillation initiative (QBOi), describes how the observed equatorial stratospheric zonal winds can be imposed in model experiments. This allows the dynamical response across different models with similar and realistic QBOs to be analysed. Using a multi-model ensemble generated by QBOi modelling centres, we present an assessment of the extratropical teleconnections in comparison with observations.

How to cite: Andrews, M., Butchart, N., Anstey, J., Bednarz, E., Elsbury, D., Kumar, V., Palmeiro, F., Trencham, N., Chai, Z., Tang, Q., Xie, J., Lin, P., Lott, F., Watanabe, S., Jaison, A., Knight, J., Naoe, H., and Yoshida, K.: Extratropical teleconnections in an ensemble of models nudged towards the observed equatorial QBO, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8621, https://doi.org/10.5194/egusphere-egu24-8621, 2024.

11:25–11:35

EGU24-20008

ECS

On-site presentation

Modulation of El Niño by the Quasi-Biennial Oscillation

Mario Rodrigo, Javier García-Serrano, and Ileana Bladé

The Quasi-Biennial Oscillation (QBO) of equatorial zonal winds is the leading mode of lower-stratospheric variability. Numerous studies have explored its connection with the troposphere, including its sensitivity to tropical convection and the El Niño-Southern Oscillation (ENSO). In particular, the upward ENSO impact on the QBO is known: observational evidence suggests that during El Niño the QBO propagates faster (shorter period). However, the potential downward QBO influence on ENSO has not been thoroughly assessed and needs better understanding. Here, we focus on the strongest ENSO events, dubbed super El Niños, characterized by extreme sea surface temperature (SST) anomalies in the eastern Pacific. Super El Niños are exceptional due to self-limiting ENSO dynamics in the tropical Pacific and seasonal SST cooling during summer and autumn, which prevents strong eastern Pacific SST warming and convective anomalies from developing. Their existence requires one or more factors external to the tropical Pacific to aid the Bjerknes feedback in building an El Niño event. In both observations and models (EC-EARTH), super El Niño events seem to require the westerly QBO phase to coincide with a growing El Niño, i.e. in boreal summer and fall. We thus propose a novel element that contributes to the generation of extreme El Niño events that involve the QBO and its modulation of the Walker circulation. While an El Niño event typically leads to a weaker Walker circulation, the weakening becomes more pronounced if the QBO is in its westerly phase. Consequently, the low-level trade wind anomalies over the equatorial Pacific are intensified, which reinforces the Bjerknes feedback and enhances the warm anomalies over the cold tongue region. Our results suggest that the QBO state could be considered to improve El Niño predictions, especially for extreme events.

How to cite: Rodrigo, M., García-Serrano, J., and Bladé, I.: Modulation of El Niño by the Quasi-Biennial Oscillation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20008, https://doi.org/10.5194/egusphere-egu24-20008, 2024.

SPARC Reanalysis Intercomparison Project (S-RIP)

11:35–11:45

EGU24-19343

Highlight

Virtual presentation

Summary of S(A)-RIP Phase 1 and Plans for Phase 2: Chemical Reanalyses & Air Quality, Tropospheric Circulation, Extreme Events, and More

Jonathon Wright, Gloria L. Manney, Mastomo Fujiwara, Krzysztof Wargan, Sean Davis, Mohamadou Diallo, Felix Ploeger, K. Emma Knowland, and Brad Weir

Reanalysis datasets are widely used to understand atmospheric processes; however, different reanalyses may give very different results for the same diagnostics. The Atmospheric Processes And their Role in Climate (APARC; formerly SPARC) Reanalysis Intercomparison Project, or S(soon to be A)-RIP (https://s-rip.github.io/), is a coordinated activity to compare key diagnostics among atmospheric reanalyses, identify differences among reanalyses and their underlying causes, provide guidance on appropriate usage of reanalyses in scientific studies, and contribute to future improvements in the reanalysis products via collaborations with reanalysis centers and data users. S-RIP Phase 1 (completed in early 2022) focused primarily on the upper troposphere and above and processes linking these regions to the troposphere and surface. We are broadening our efforts in Phase 2 (S-RIP2), with new directions including studies of the tropospheric circulation, extreme weather events, and their links to the stratosphere, along with evaluation of chemical reanalyses, both those with a stratosphere / upper troposphere focus and those that focus on air quality applications. This presentation will provide a summary of Phase 1 results and discussion of future directions for S-RIP2, emphasizing applications to composition and chemistry studies and capacity building for Early Career Scientists.

How to cite: Wright, J., Manney, G. L., Fujiwara, M., Wargan, K., Davis, S., Diallo, M., Ploeger, F., Knowland, K. E., and Weir, B.: Summary of S(A)-RIP Phase 1 and Plans for Phase 2: Chemical Reanalyses & Air Quality, Tropospheric Circulation, Extreme Events, and More, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19343, https://doi.org/10.5194/egusphere-egu24-19343, 2024.

Discussion Post a comment

11:45–11:55

EGU24-7531

On-site presentation

Cloud climatologies from reanalysis datasets – an intercomparison

Axel Lauer, Lisa Bock, and Birgit Hassler

Through their significant impact on the short- and longwave radiation and their pivotal role in the hydrological cycle, clouds and their response to climate change are a key component in present-day and future climate. As part of the SPARC Reanalysis Intercomparison Project (S-RIP) phase 2, we analyze cloud climatologies from twelve reanalysis datasets including, for instance, ERA5, MERRA2 and JRA-55. The study focuses on parameters that are available from most reanalysis datasets such as cloud fraction, cloud liquid and ice water content as well as cloud radiative effects on monthly to multi-year time scales. Geographical distributions, variability and statistical properties of the cloud parameters from the reanalyses for specific cloud regimes and regions are compared and put into context with satellite observations. First results show that more recent reanalysis products are in closer agreement with the satellite data and that in contrast to multi-model means of models participating in the Coupled Model Intercomparison Project (CMIP), multi-reanalysis means do not outperform individual reanalyses. For a consistent processing of all reanalysis and satellite datasets, the Earth System Model Evaluation Tool (ESMValTool) is applied. ESMValTool is a community developed open-source software tool that provides common operations such regridding data onto the same grid, masking of missing values, area extraction, and basic statistics such as seasonal means, annual means, area means, etc. which facilitates analysis and a fair intercomparison of the datasets. For comparison with satellite data, multiple products for each parameter are used to estimate observational uncertainties.

How to cite: Lauer, A., Bock, L., and Hassler, B.: Cloud climatologies from reanalysis datasets – an intercomparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7531, https://doi.org/10.5194/egusphere-egu24-7531, 2024.

Polar Ozone and Polar Stratospheric Clouds

11:55–12:05

EGU24-7337

On-site presentation

Peculiarities and trends in the vertical ozone distribution 1973 - 2023 at Faraday/Vernadsky Antarctic station

Yulia Andrienko, Asen Grytsai, Gennadi Milinevsky, Jonathan Shanklin, Yu Shi, Ruixian Yu, and Oleksandr Poluden

We processed vertical ozone distribution measurements from the Faraday/Vernadsky station made by the Umkehr method for the 1973–2023 period. Ozone profiles in this unique series of ozone observations since 1973 cover pre-ozone hole times and the ozone hole period. Umkehr data from about 1200 Dobson spectrophotometer observations was processed using the UMK92 ozone profile retrieval algorithm. The Faraday/Vernadsky station is located at the edge of the ozone hole area; therefore, the total ozone column values over the station can change rapidly. This feature is seen clearly in Umkehr profiles measured during the same day in the morning and evening. In the pre-ozone hole period 1973–1983, the ozone partial column in ozone profiles maximum varies from 134 DU/layer to 56 DU/layer with the altitude of the profile maximum at 14–18 km. Profiles in ozone hole conditions usually have two maxima. The altitude area of significant depletion in ozone partial column values between these maxima located in the usual highest ozone concentration height. The values in altitudes at expected ozone maximum drop to 14–26 DU/layer. The 50-year trend in ozone profiles in the atmosphere above Faraday/Vernadsky station from pre-ozone hole times till 2023 is described and discussed.

How to cite: Andrienko, Y., Grytsai, A., Milinevsky, G., Shanklin, J., Shi, Y., Yu, R., and Poluden, O.: Peculiarities and trends in the vertical ozone distribution 1973 - 2023 at Faraday/Vernadsky Antarctic station, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7337, https://doi.org/10.5194/egusphere-egu24-7337, 2024.

12:05–12:15

EGU24-1509

ECS

Highlight

On-site presentation

Future volcanic eruptions delay stratospheric ozone recovery

Man Mei Chim, Thomas J. Aubry, Nathan Luke Abraham, and Anja Schmidt

At present, volcanic sulfate aerosols can lead to stratospheric ozone loss under the presence of anthropogenic chlorofluorocarbons (CFCs). Recent satellite measurements showed that the 2015 Calbuco eruption, a small-magnitude eruption in Chile with 0.4 Tg of stratospheric sulfur injection, caused large-scale stratospheric ozone depletion during October 2015 in the Antarctic. According to the World Meteorological Organization, atmospheric CFC levels have declined since the 1980s, and the Antarctic ozone hole is expected to be healed by around mid-century. In the absence of CFCs, future volcanic eruptions producing stratospheric volcanic sulfate aerosol are expected to increase stratospheric ozone column concentrations. However, it remains uncertain whether future volcanic eruptions will lead to an earlier or a delayed recovery in stratospheric ozone back to 1980s levels.

To investigate how future volcanic eruptions affect stratospheric ozone recovery, we generated stochastic future eruption scenarios based on an array of bipolar ice cores, satellite measurements and geological records. We then selected the low-end, median and high-end future stochastic scenarios to perform simulations from 2015 to 2100 using a plume-aerosol-chemistry-climate modelling framework, UKESM-VPLUME with interactive volcanic aerosols. Our model results show that future volcanic eruptions can delay the recovery of the global stratospheric ozone column, as opposed to a previous modelling study that suggested future eruptions will lead to an earlier recovery of the global stratospheric ozone column. In addition, our stochastic scenarios show that future eruptions can potentially delay the recovery of Antarctic total ozone column by 2 to 3 years, depending on the timing, magnitude and latitude of the eruptions. Our results offer insights into the role of future volcanic eruptions in affecting global and polar stratospheric ozone recovery. We also highlight the importance of incorporating interactive volcanic sulfate aerosols in future modelling studies to assess the impact of volcanic eruptions on stratospheric ozone.

How to cite: Chim, M. M., Aubry, T. J., Abraham, N. L., and Schmidt, A.: Future volcanic eruptions delay stratospheric ozone recovery, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1509, https://doi.org/10.5194/egusphere-egu24-1509, 2024.

12:15–12:25

EGU24-6876

Highlight

Virtual presentation

The Influence of Stratospheric Hydration from the Hunga Eruption on Chemical Processing in the Stratospheric Winter Polar Vortices

Michelle Santee, Gloria Manney, Alyn Lambert, Luis Millan, Nathaniel Livesey, Michael Pitts, Lucien Froidevaux, and William Read

The January 2022 eruption of the undersea Hunga volcano injected an unprecedented amount of water vapor directly into the stratosphere. In this talk, we will use measurements of gas-phase constituents from Aura MLS (Microwave Limb Sounder) and polar stratospheric clouds (PSCs) from CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) on CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) together with meteorological reanalyses to investigate how the extraordinary stratospheric hydration and accompanying anomalies in stratospheric temperature and circulation from Hunga affected chemical processing and ozone destruction in the polar lower stratosphere. We will focus on the Antarctic ozone hole season of 2023, when the excess moisture led to unusually early and vertically extensive PSC activity and heterogeneous chlorine activation (i.e., depleted HCl and enhanced ClO) in early winter. Although unmatched in the satellite record, the early-winter upper-level chlorine activation was insufficient to induce substantial ozone loss. Chlorine activation, denitrification, and dehydration processes saturated in midwinter, with trace gas evolution essentially following the climatological mean thereafter. Thus, despite the exceptional early-winter conditions, cumulative ozone losses in the 2023 austral spring were mostly unremarkable because stratospheric chemical processing saturated, as typically happens in the Antarctic. We will also discuss the 2022 Antarctic winter, when the Hunga plume was effectively excluded from the southern polar region by the strong transport barrier at the edge of the vortex. As a result, Hunga had little effect on either the vortex itself or the chemical processing and ozone loss that took place within it during the 2022 Antarctic winter/spring. Finally, we will touch briefly on the influence of Hunga on the 2023/2024 Arctic winter that will have just concluded.

How to cite: Santee, M., Manney, G., Lambert, A., Millan, L., Livesey, N., Pitts, M., Froidevaux, L., and Read, W.: The Influence of Stratospheric Hydration from the Hunga Eruption on Chemical Processing in the Stratospheric Winter Polar Vortices, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6876, https://doi.org/10.5194/egusphere-egu24-6876, 2024.

Posters on site: Mon, 15 Apr, 10:45–12:30 | Hall X5

Display time: Mon, 15 Apr 08:30–Mon, 15 Apr 12:30

Chairpersons: Thomas Reichler, Masatomo Fujiwara, Gabriel Chiodo

Joint Posters session of Stratospheric Dynamics & Chemistry

X5.1

EGU24-18226

Reconciling long-term stratospheric circulation changes from ERA5 and CCMI2

Mohamadou A. Diallo, Roland Eichinger, Fernando Iglesias-Suarez, Aleš Kuchař, and Michaela I. Hegglin

Climate models predict a global acceleration of the stratospheric Brewer-Dobson circulation (BDC) induced by rising greenhouse gas (GHG) levels. However, this predicted strengthening of the BDC has not yet been compared with long-term observations, due to the scarcity of long-term observation records.

The recent release of ERA5 long-term reanalysis data covering the period from 1950 to the present day offers new opportunities to assess the robustness of the projected BDC acceleration. These observation-based data make it possible to assess the ability of models to capture the impact of natural variability such as the Quasi- Biennial Oscillation (QBO), the El Nino Southern Oscillation (ENSO), the solar cycle, stratospheric volcanic aerosols and the Pacific Decadal Oscillation (PDO), on circulation changes and their interaction.

In this presentation, I will review our knowledge of the dynamical mechanisms explaining changes in the BDC over the period 1960-2018 using ERA5 and CCMI-2. I will then highlight the impact of climate variability modes (e.i. QBO, ENSO, Solar, volcanoes and PDO) and their interaction on the BDC. Finally, I will discuss the robustness and main reasons for differences between modern reanalyses and climate models in the BDC changes.

How to cite: Diallo, M. A., Eichinger, R., Iglesias-Suarez, F., Kuchař, A., and Hegglin, M. I.: Reconciling long-term stratospheric circulation changes from ERA5 and CCMI2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18226, https://doi.org/10.5194/egusphere-egu24-18226, 2024.

X5.2

EGU24-2752

Highlight

Warmer Antarctic summers in the last two decades linked to earlier stratospheric final warming occurrences

Hyesun Choi, Hataek Kwon, Seong-Joong Kim, and Baek-Min Kim

We proposed a link between the interannual and decadal variability in Antarctic surface climate during the austral summertime (December-January) and the timing of stratospheric final warming (SFW) occurrences. This connection is based on 44 years of reanalysis data and in-situ observation spanning from 1979 to 2023. Positive surface pressure anomalies over Antarctica, associated with an earlier occurrence of SFW, develop through stratosphere-troposphere downward coupling, which leads to a warmer surface in Antarctica, except for the Antarctic Peninsula where a cooler surface is observed. On the contrary, the surface pressure and temperature anomalies associated with the later occurrence of SFW exhibit almost opposite or weaker behaviors. Congruence analyses support that a trend towards earlier SFW occurrences can explain the pause of the cooling trend or a slight reversal into the warming trend of the interior Antarctic surface through strengthening anti-cyclonic surface circulation since the 2000s. The resulting surface temperature responses can leave imprints on sea-ice concentration trends in the high-latitude Southern Hemisphere, displaying the dipole anomalies with an increase and a decrease of sea ice over the Antarctic Peninsula and northern Ross Sea, respectively.

How to cite: Choi, H., Kwon, H., Kim, S.-J., and Kim, B.-M.: Warmer Antarctic summers in the last two decades linked to earlier stratospheric final warming occurrences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2752, https://doi.org/10.5194/egusphere-egu24-2752, 2024.

X5.3

EGU24-4617

Antarctic tropopause by ozonesonde profiles from the Polar Atmospheric Chemistry at the Tropopause PACT database

Gennadi Milinevsky, Oksana Ivaniha, Andrew Klekociuk, Ruixian Yu, Oleksandr Evtushevsky, Asen Grytsai, and Yu Shi

Stratosphere–troposphere exchange can be considered globally within the framework of the atmosphere's general circulation as the transfer of air masses through the tropopause with ascending (descending) flows in the tropics (extratropical latitudes). The report aims to study the features and behavior of thermal and chemical tropopause to determine the troposphere-stratosphere interaction in the ozone hole in the Antarctic region. To calculate the height of the polar tropopause based on vertical temperature profiles (thermal tropopause), ozone profiles (ozone tropopause), and water vapor ("water" tropopause), we used the Polar Atmospheric Chemistry at the Tropopause (PACT) database that provides high-resolution measurements from polar ozonesondes flown from selected Antarctic sites. The vertical resolution of the raw ozonesonde measurements is typically 10 meters, which allows us to determine the tropopause height with high accuracy. We calculated the monthly mean ozone and thermal tropopause height variations from the PACT data. Seasonal thermal tropopause and ozone tropopause height monthly changes at the selected Antarctic stations were examined. We developed an algorithm for determining the tropopause height based on vertical profiles of water vapor, studied the relative position of the three tropopauses by altitude, and revealed the anticorrelation of the water and thermal tropopauses. The analysis shows that during the ozone hole formation period in August–September, the vertical stability of the upper troposphere and lower stratosphere is disturbed, and the ozone tropopause can drop below the thermal one, which can create conditions for the spread of stratospheric air into the troposphere and cause conditions for the stratosphere–troposphere exchange.

This work was partly supported by the projects of the Australian Antarctic Division and by the International Center of Future Science, Jilin University, under Grant No G2023129024.

How to cite: Milinevsky, G., Ivaniha, O., Klekociuk, A., Yu, R., Evtushevsky, O., Grytsai, A., and Shi, Y.: Antarctic tropopause by ozonesonde profiles from the Polar Atmospheric Chemistry at the Tropopause PACT database, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4617, https://doi.org/10.5194/egusphere-egu24-4617, 2024.

X5.4

EGU24-8901

Station versus reanalysis-based proxies for the Quasi-Biennial Oscillation (QBO): How do they differ – and does it matter?

Peter Braesicke, Benjamin Ertl, and Tobias Kerzenmacher

The Quasi-Biennial Oscillation (QBO) has long been recognized as an important factor shaping hemispheric large-scale dynamics, in particular serving as a sort of switch for polar vortex dynamics in the Northern Hemisphere (NH). When calculating (extratropical) correlations or composites for different phases of the QBO some subjective choices have to be made, including “Which timeseries should be used?” or “How to define the phasing?”.

Here, we will examine - from a historical perspective - the differences between a traditional station based QBO timeseries (specifically, the “Singapore” zonal wind timeseries provided by the Free University of Berlin and currently continued at the Karlsruhe Institute of Technology) in contrast to reanalysis based timeseries (specifically, zonal mean zonal wind timeseries from ERA5, and near station profiles from ERA5 corresponding to the station’s location).

We explore the climatological properties of the QBO, including composites and phase transitions. Additionally, we examine how the choice of QBO proxy relates to and influences the perception and interpretation of the Holton-Tan relationship, which describes the potential link between the phases of the QBO and the strength of the stratospheric polar vortex – in particular during NH winter.

Data and tools are accessible via the ATMOHub at https://www.atmohub.kit.edu/.

How to cite: Braesicke, P., Ertl, B., and Kerzenmacher, T.: Station versus reanalysis-based proxies for the Quasi-Biennial Oscillation (QBO): How do they differ – and does it matter?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8901, https://doi.org/10.5194/egusphere-egu24-8901, 2024.

Discussion Post a comment

X5.5

EGU24-15844

ECS

Scale selection of mixed Rossby-gravity waves through wave-mean flow interactions

Sándor István Mahó, Nedjeljka Žagar, and Sergiy Vasylkevych

Mixed Rossby-gravity (MRG) waves contribute significantly to tropical variability in the upper troposphere and the stratosphere. Studies based on reanalysis data suggest that the scale of MRG waves in the two regions is different, with the troposphere dominated by synoptic-scale MRG waves, while the MRG waves in the stratosphere have planetary scales. Using the recently discovered excitation mechanism of the MRG waves by wave-mean flow interactions, we investigate whether this mechanism can explain the different scale selection in the troposphere and the stratosphere.

We carry out high-accuracy numerical simulations with a spherical shallow water model (TIGAR) that includes the MRG wave as a subset of prognostic variables. This framework allows to identify wave-mean flow interactions as the main driver of MRG scale selection in comparison with excitation driven by external forcing and wave-wave interactions. Simulations with idealized background zonal wind field and profiles derived from ERA5 reanalysis from 1 and 200 hPa show that the jet position is a decisive factor for the MRG scale selection. Particularly, when the jet is located closer to the equator, as in boreal winter in the troposphere, synoptic-scale MRG waves are excited. In the case of jets embedded well in extratropics (40-50°), such as in the upper stratosphere, wave-mean flow interactions generate MRG waves with planetary scales. These results explain the MRG scale selection in the upper troposphere and the stratosphere by a single mechanism and highlight the importance of representing accurately wave-mean flow interactions in climate models.

How to cite: Mahó, S. I., Žagar, N., and Vasylkevych, S.: Scale selection of mixed Rossby-gravity waves through wave-mean flow interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15844, https://doi.org/10.5194/egusphere-egu24-15844, 2024.

X5.6

EGU24-13273

Spatial Distribution of Mixing and Transport in the Northern Middle Atmosphere

Jezabel Curbelo and Carlos R. Mechoso

We apply a novel approach to studying eddy mixing and transport in the northern middle atmosphere during winter (December-January-February), based on the concept of Lagrangian diffusivity – a measure of how quickly air parcels mix together. Unlike traditional diagnostics that rely on longitudinal or contour-based averages, Lagrangian diffusivity provides a detailed three-dimensional view of the mixing process. Our formulation of Lagrangian diffusivity requires the calculation of parcel trajectories, performed on isentropic surfaces using ERA5 reanalysis data. Additionally, we have applied several diagnostic techniques to contextualize our results on Lagrangian diffusivity within the broader framework of the stratospheric polar vortex and quasi-geostrophic wave properties. Specifically, we investigate the influence of quasi-geostrophic motions on the stratospheric polar vortex using wave activity flux and local wave activity. Furthermore, we employ a Lagrangian descriptor, a tool based on parcel trajectory length, to locate the boundary of the stratospheric polar vortex (SPV).

The results reveal pronounced zonal asymmetries in Lagrangian diffusivity and wave activity flux. Mixing is highest at mid-latitudes around the prime meridian and at locations within the SPV. Local wave activity is elevated at high latitudes and upstream of the climatological vortex boundary opening, highlighting the role of quasi-geostrophic waves in the southward displacement of mid-latitude westerlies.

How to cite: Curbelo, J. and Mechoso, C. R.: Spatial Distribution of Mixing and Transport in the Northern Middle Atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13273, https://doi.org/10.5194/egusphere-egu24-13273, 2024.

X5.8

EGU24-16480

Improving the in situ observation-based long-term record of stratospheric age of air

Johannes Laube, Elliot Atlas, Kyriaki Blazaki, Huilin Chen, Andreas Engel, Pauli Heikkinen, Rigel Kivi, Elinor Tuffnell, Thomas Wagenhäuser, and Christian Rolf

Stratospheric mean age of air is an important metric and much-used proxy for the speed of the residual overturning circulation in the stratosphere. Much effort has been put into better constraining observation-based estimates of age of air over the past two decades. Yet substantial uncertainties remain for some aspects such as the long-term evolution, especially at higher altitudes that are hard to reach for most in situ-measurement platforms.

We here present a newly derived age of air data set, which is based on high precision measurements of inert trace gases that were derived from a) AirCore samples from multiple weather balloon-based deployments since 2017 (updated from Laube et al., 2020), and also b) recently collected as well as archived reanalysed air samples from high altitude aircraft and large balloon campaigns between 1976 and 2017. Utilised trace gases include SF₆, C₂F₆, C₃F₈, CHF₃ (HFC-23), and C₂HF₅ (HFC-125), all of which have been proven to be suitable as age tracers (Leedham Elvidge et al., 2018). We evaluate the uncertainties connected to the trace gas measurements as well as the derivation of the mean age of air, and compare our estimates to published data sets such as the one from Engel et al. (2017).

References

Engel, et al., Atmos. Chem. Phys., 2017, https://doi.org/10.5194/acp-17-6825-2017.

Laube et al., Atmos. Chem. Phys., 2020, https://doi.org/10.5194/acp-20-9771-2020.

Leedham Elvidge et al., Atmos. Chem. Phys., 2018, https://doi.org/10.5194/acp-18-3369-2018.

How to cite: Laube, J., Atlas, E., Blazaki, K., Chen, H., Engel, A., Heikkinen, P., Kivi, R., Tuffnell, E., Wagenhäuser, T., and Rolf, C.: Improving the in situ observation-based long-term record of stratospheric age of air , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16480, https://doi.org/10.5194/egusphere-egu24-16480, 2024.

X5.9

EGU24-12185

Effects of two typical gravity wave processes on stratospheric ozone over the Tibetan Plateau based on radiosonde data

Shujie Chang, Haotian He, Xiangdong Zheng, Lingfeng Wan, and Jundong Wang

This study analyzes the formation process and propagation characteristics of two typical gravity wave events that occurred over the Tibetan Plateau, based on the radiosonde data from Naqu Station on August 4, 2011 at 7:00-12:00UTC and August 13, 2011 at 8:00-12:00 UTC, as well as the global climate fifth-generation atmospheric reanalysis dataset (ERA5) provided by the European Centre for Medium-Range Weather Forecasts (ECMWF). The effects of the two gravity wave events on ozone are also analyzed. The results show that two gravity wave processes were broken in the tropopause and upper stratosphere respectively. The gravity wave event on August 4 captured the signal well at 400 hPa, showing a northwest-southeast structure and gradually tilting eastward. The signal decayed between 7:00-9:00 UTC, and the gravity wave completely broke and released energy near 150 hPa at 10:00 UTC. The ozone significantly decreased in the region of 200-50 hPa due to ozone exchange between the upper troposphere and lower stratosphere (UTLS). The results on August 13 showed that the gravity wave propagated from the middle stratosphere to the upper stratosphere, exhibiting a northeast-southwest structure and gradually tilting eastward. The signal weakened from the middle stratosphere at 8:00 UTC, and it broke and released energy near 7 hPa at 10:00 UTC. The ozone concentration increased in the region of 20-3 hPa. Both gravity wave events resulted in a decrease in ozone at the tropopause (200-150 hPa) and upper stratosphere (20-3 hPa), mainly due to the mixing of the upper and lower atmospheric layers caused by the gravity wave breaking, leading to ozone exchange.

How to cite: Chang, S., He, H., Zheng, X., Wan, L., and Wang, J.: Effects of two typical gravity wave processes on stratospheric ozone over the Tibetan Plateau based on radiosonde data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12185, https://doi.org/10.5194/egusphere-egu24-12185, 2024.

X5.11

EGU24-15870

Highlight

Coupling between severe weather events and the middle atmosphere, potentially affecting even the ionospheric heights

Kateřina Potužníková, Michal Kozubek, Petra Koucká Knížová, and Jaroslav Chum

X5.12

EGU24-13938

Highlight

New evidence for CH4 enhancement at upper troposphere associated with Asian summer monsoon

Zhaonan Cai, Mengchu Tao, Sihong Zhu, Yi Liu, Liang Feng, Shuangxi Fang, You Yi, and Jianchun Bian

The Asian Summer Monsoon (ASM) region is key region transporting air to the upper troposphere, significantly influencing the distribution and concentration of trace gases, including methane (CH₄), an important greenhouse gas. We investigate the seasonal enhancement of CH₄ in the upper troposphere over the ASM region, utilizing retrievals from the Atmospheric Infrared Sounder (AIRS), model simulations and in-situ measurements. Both AIRS data and model simulation reveal a substantial seasonal increase in CH₄ concentrations of up to 3%, aligning with the active monsoon period. Notably, the spatial distribution of the methane plume demonstrates a southwestward shift in the AIRS retrievals, in contrast to the model simulations which predict a broader enhancement, including a significant increase to the east. A cross-comparison with in-situ measurements, including AirCore measurements over Tibetan Plateau and airline sampling across the Asian summer monsoon anticyclone (ASMA), favors the enhancement represented by model simulation. Remarkable CH₄ enhancement over west Pacific is also evidenced by in-situ data and simulation as dynamical extension of ASMA. Our findings underscore the necessity for cautious interpretation of satellite-derived methane distributions and highlights the critical role of in-situ data in anchoring the assimilation of CH₄.

How to cite: Cai, Z., Tao, M., Zhu, S., Liu, Y., Feng, L., Fang, S., Yi, Y., and Bian, J.: New evidence for CH4 enhancement at upper troposphere associated with Asian summer monsoon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13938, https://doi.org/10.5194/egusphere-egu24-13938, 2024.

X5.13

EGU24-10246

Rapid chlorine deactivation at very low ozone concentrations in the Antarctic stratosphere

Jens-Uwe Grooß, Rolf Müller, and Ralph Lehmann

The intensive catalytic chemical ozone loss cycles involving inorganic chlorine compounds are known to cause the ozone hole, that regularly forms in the Antarctic polar vortex each winter and spring. One key point of the explanation of the ozone hole are heterogeneous reactions on the surface of Polar Stratospheric Cloud (PSC) particles, which are present in the polar stratosphere owing to the very low stratospheric temperatures.

Ozone mixing ratios can reach values of a few ppbv which is below detection limit of ozone sonde observations. Under these extreme conditions, fast chlorine deactivation into the reservoir HCl does occur even though polar stratospheric clouds are still present, that are normally causing chlorine activation.

In this study we revisit this issue and investigate the occurring chlorine chemistry in more detail. The explanation of the chemical mechanism of the fast net HCl formation is based on the automatic determination of reaction pathways by the Pathway Analysis Program (PAP) (Lehmann, 2004).

The simulations of chemical composition are performed by the model CLaMS in box model mode along an ensemble of about 600 trajectories in the Antarctic spring 2018. The simulated rapid complete chlorine deactivation into HCl in the presence of PSCs is in line with satellite observations by the Microwave Limb Sounder (MLS).

Reference
Lehmann, R.: An algorithm for the determination of all significant pathways in chemical reaction systems, J. Atmos. Chem. 47, 45-78 (2004).

How to cite: Grooß, J.-U., Müller, R., and Lehmann, R.: Rapid chlorine deactivation at very low ozone concentrations in the Antarctic stratosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10246, https://doi.org/10.5194/egusphere-egu24-10246, 2024.

X5.14

EGU24-15811

Relationship between appearance of polar stratospheric clouds and ozone destruction over Northern polar region in 2011 and 2020 based on CALIPSO observations

Hideaki Nakajima, Miu Ogawa, Kazuyuki Kita, and Michael C. Pitts

Although stratospheric ozone loss occurs every year in Antarctica, Arctic ozone loss occurs only when stratospheric temperature gets low. Recently, substantial ozone loss occurred in Arctic in 1997, 2011, and 2020. Especially, the magnitude of Arctic ozone losses in 2011 and 2020 was comparable to that of in Antarctica. Satellite CALIPSO was launched in 2006, and is still in operation and measuring global cloud properties using two-wavelength lidars. It measures distribution and characteristics of polar stratospheric clouds (PSC) over both polar regions. In this study, we analyzed characteristics of Arctic PSCs in 2011 and 2020, and their effects on polar ozone loss. Figure 1 (not shown in this abstract) shows distribution and types of Arctic PSCs along a CALIPSO satellite track on 4 January 2011 over downstream of Greenland. The appearance of wave-ice-type PSC due to mountain-induce lee wave can be seen.

In this analysis, distribution and types of Arctic PSC was analyzed for the altitudes of 20, 17.5, and 15 km for each CALIPSO orbit (15 orbits per day in maximum) from January to March in 2011 and 2020. Local temperature and HNO₃ amount by Aura/MLS were also analyzed to see the PSC formation condition and the magnitude of denitrification. As a result, there were no major differences between the appearance of PSCs in January and February. However, stratospheric temperature was low in 2020 compared with 2011 in March, and appearance of PSC was greater in 2020. Ozone depletion started to occur in March when sunlight was available over the Arctic, and record-high ozone depletion was observed in 2020. The reason of this low temperature in 2020 could be attributed to the unusually strong polar vortex over the Arctic in this year.

How to cite: Nakajima, H., Ogawa, M., Kita, K., and Pitts, M. C.: Relationship between appearance of polar stratospheric clouds and ozone destruction over Northern polar region in 2011 and 2020 based on CALIPSO observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15811, https://doi.org/10.5194/egusphere-egu24-15811, 2024.

X5.15

EGU24-3124

ECS

ENSO Modoki impacts on the Interannual Variations of Spring Antarctic Stratospheric Ozone

Yingli Niu

Using observation and reanalysis data, we investigated the effect of the sea surface temperature anomalies associated with ENSO Modoki from September to October on interannual variations in Antarctic stratospheric ozone from October to November. It was found that the planetary wave anomalies generated by ENSO Modoki in the tropical troposphere propagate to the southern mid- and then high-latitude stratosphere. The planetary wave anomalies have a profound impact on the polar vortex, subsequently affecting the interannual variations in Antarctic stratospheric ozone. Further analysis revealed that the responses of the polar vortex and ozone to ENSO Modoki are mainly modulated by the wave-1 and wave-3 components, and the effect of wave-2 is opposite and offset by those of wave-1 and wave-3. The contribution of the residual waves (after removing waves 1, 2 and 3, and the remaining waves) are relatively small. Furthermore, we evaluated the performance of CMIP6 models in simulating the impacts of ENSO Modoki on the southern stratospheric polar vortex and ozone. We selected seven models, that include stratospheric processes and stratospheric chemical ozone. We found that all of them can capable of distinguishing between eastern Pacific ENSO and ENSO Modoki events. However, only GISS-E2-1-G and MPI-ESM-1-2-HAM can simulate the patterns of ozone, circulation and temperature in the Southern Hemisphere in a manner that closely resembles the reanalysis results. Further analysis indicated that these two models can better simulate the propagation of planetary wave activities in the troposphere forced by ENSO Modoki, whereas the other models produce significantly different results to those obtained from observations.

How to cite: Niu, Y.: ENSO Modoki impacts on the Interannual Variations of Spring Antarctic Stratospheric Ozone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3124, https://doi.org/10.5194/egusphere-egu24-3124, 2024.

X5.16

EGU24-5022

Antarctic total ozone longitude–latitude dependence on sudden stratospheric warmings

Asen Grytsai, Ruixian Yu, Alina Burmay, Gennadi Milinevsky, Oleksandr Evtushevsky, Andrew Klekociuk, Oleksandr Poluden, Xiaolong Wang, Yu Shi, and Oksana Ivaniha

We use Multi-Sensor Reanalysis and ground-based total ozone content (TOC) data to study total ozone variations in Antarctica near the dates of sudden stratospheric warmings (SSW). Three events were analyzed, including the warmings in 1988, 2002 (major warming), and 2019. All of them occurred in September, during the period of ozone hole development. Total ozone over stations with different latitudes and longitudes was considered to understand the properties of its variations in different parts of the stratospheric polar vortex and over the surrounding area. The 1979–2022 TOC climatology was obtained from the Multi-Sensor Reanalysis data. The multi-year mean shows a main total ozone minimum in September–October with values lower than 200 Dobson Units (DU) in the Atlantic longitudinal sector (Rothera, Faraday/Vernadsky). The annual TOC maximum of 280–300 DU occurs at the Antarctic stations, mainly in December. The exception is Dumont-d’Urville, located in the zonal maximum region and characterized by higher ozone levels of about 340 DU, which are reached in October–November. Composite analysis is carried out to study the interrelation between SSW events and total ozone variations. We considered a time range covering 60 days before and 60 days after an SSW. Of course, three events do not allow proper statistical material, but some tendencies can be traced. Preliminarily, there is a TOC increase by ~100 DU at Amundsen-Scott (located at the South Pole) near the SSW date. The corresponding increase in the Atlantic longitudinal sector (Rothera, Faraday/Vernadsky, and even mid-latitude Ushuaia station) occurred several days later. It is noticed that after several weeks, TOC values in the Atlantic sector become lower than climatological ones, which a partial recovery of the polar vortex can cause. In the opposite Australian longitudinal sector, TOC values are maintained over the climatological level by tens of DU at least 30–40 days before the SSW. Consequently, the SSW events seem to be prepared by stratospheric processes connected with the intensification of the TOC zonal maximum.

This work was partly supported by the projects of the Australian Antarctic Division and by the International Center of Future Science, Jilin University, under Grant No G2023129024.

How to cite: Grytsai, A., Yu, R., Burmay, A., Milinevsky, G., Evtushevsky, O., Klekociuk, A., Poluden, O., Wang, X., Shi, Y., and Ivaniha, O.: Antarctic total ozone longitude–latitude dependence on sudden stratospheric warmings, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5022, https://doi.org/10.5194/egusphere-egu24-5022, 2024.

X5.17

EGU24-8591

ECS

Statistical Characteristics of the Long-Term Variations in Major Sudden Stratospheric Warming Events

Yuli Zhang, You Yi, Xiaoyu Ren, and Yi Liu

We investigate the statistical characteristics and the long-term variations of major sudden stratospheric warming (SSW) events in the Northern Hemisphere. We find that the strength and duration of major SSW events have increased from 1958 to 2019 and that this is due to the strengthening of the winter planetary wave activity. We find that the frequency of displacement and split SSW events differs between early, middle, and late winter. Early and middle winter are dominated by displacement and split SSW events, respectively, but the frequency of the two types of events is almost equal in late winter. This is due to the differences in the relative strength of wavenumber-1 and wavenumber-2 planetary wave activity in the three winter periods. As a result of the increase in upward planetary wave activity and the decrease in westerly winds around the polar vortex in middle winter, a shift in the timing of SSW events toward middle winter is detected. In addition, we revealed the influence of the downward propagation of different types of SSW events on the surface temperature anomaly. There were surface cold centers in Russia and northern China after the middle split SSW events; by contrast, there were more cold events in North America after the middle split SSW events.

How to cite: Zhang, Y., Yi, Y., Ren, X., and Liu, Y.: Statistical Characteristics of the Long-Term Variations in Major Sudden Stratospheric Warming Events , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8591, https://doi.org/10.5194/egusphere-egu24-8591, 2024.

X5.18

EGU24-2032

QBO-composite mean meridional circulation: ERA5 and MIPAS tracer-derived residual velocities

Tobias Kerzenmacher, Udo Grabowski, Thomas von Clarmann, and Gabriele Stiller

This study focuses on analyzing the Quasi-Biennial Oscillation (QBO)-composite mean meridional circulation during the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) measurement period 2002 to 2012, using both ERA5 reanalysis and MIPAS tracer-derived velocities. The investigation employs the approach described in the S-RIP report: We have deseasonalized QBO-W onsets at 20 hPa and have compared zonal-mean vertical and meridional velocities extracted from MIPAS tracer measurements with reanalysis data from ERA5.

To infer the effective transport velocities and mixing coefficients of the 2-D atmosphere, we employ a direct inversion technique utilizing tracer measurements from MIPAS (Clarmann and Grabowski 2016). This method involves the integration of the continuity equation over time and determines those vertical and meridional mean velocities that best reproduce the measured trace gas distributions. The advantage of the method is that it does not involve a dynamic model; instead it provides independent observation-based information on the mean meridional circulation.

This inversion method is applied to MIPAS monthly zonal mean tracer measurements of the years 2002 to 2012. This study reveals QBO patterns in tracer-retrieved velocities within the mean circulation. Observed structures compare favourably with S-RIP reanalysis results. Quantitative comparisons reveal differences that have the potential to pinpoint certain processes that might not be adequately represented in the models or deficiencies in the tracer-based inversion of the continuity equation.

These results underscore the utility of MIPAS tracer measurements for enhancing the understanding and modeling of mean-meridional circulation in Earth's atmosphere.

Reference

von Clarmann, T. and Grabowski, U.: Direct inversion of circulation and mixing from tracer measurements – Part 1: Method, Atmos. Chem. Phys., 16, 14563–14584, https://doi.org/10.5194/acp-16-14563-2016, 2016.

How to cite: Kerzenmacher, T., Grabowski, U., von Clarmann, T., and Stiller, G.: QBO-composite mean meridional circulation: ERA5 and MIPAS tracer-derived residual velocities , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2032, https://doi.org/10.5194/egusphere-egu24-2032, 2024.

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X5.19

EGU24-6682

Moist bias in the Pacific upper troposphere and lower stratosphere (UTLS) in climate models affects regional circulation patterns

Felix Ploeger, Thomas Birner, Edward Charlesworth, Paul Konopka, and Rolf Müller