The downward coupling between the stratosphere and the troposphere, as occurs during sudden stratospheric warmings (SSWs) or strong polar vortex events, can have a detectable impact on surface weather in winter, especially over Europe and the North Atlantic. These changes include shifts in the pathways of extratropical cyclones and the associated change in the location of the risk of extreme winds, flooding, or heavy snowfall.
As changes in the stratospheric circulation contribute to predictability at the surface, understanding the stratospheric drivers to surface weather - from precursors to hazards and impacts - is essential for enhancing societal preparedness and building effective early warning systems for these events. However, there has been no systematic effort to quantify the impacts with respect to stratospheric forcing.
This work establishes the connection between stratospheric extremes and midlatitude storm damage and flooding events in the Euro-Atlantic region using a combination of ERA5 reanalysis and multiple impact datasets for the period 1998-2023. We show that stratospheric extremes contribute up to 34% of the total counts of storm-related disasters and up to 12% of flood-related disasters in Europe during winter. The geographic distribution of storm-related disasters is influenced by stratospheric forcing, with more frequent storm impacts found over Scandinavia, northern and central Europe and the UK following strong vortex events as compared to the period after SSW events.
Furthermore, using multi-model ensemble of climate models (CMIP6) under future socio-economic scenarios, we examine the variability of extreme storms over the Euro-Atlantic region and investigate their connection to stratospheric drivers and biases in present-day climate and under climate change. Quantifying the connections between stratospheric drivers and surface extremes across various timescales can enable earlier warnings and risk mitigation in both present-day climate and under climate change conditions.
How to cite: Afargan Gerstman, H., Wu, R., and Domeisen, D.: Stratospheric Drivers of Extreme Weather: Implications for European Storm Damage and Flood Risk, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18971, https://doi.org/10.5194/egusphere-egu25-18971, 2025.
Using observations, reanalysis data sets, a linear barotropic model, and a state-of-art chemistry-climate model, we investigated the influence of Arctic stratospheric polar vortex (SPV) and ozone variabilities on surface air temperature (SAT) and precipitation in Asia. An out‐of‐phase interannual linkage between the SPV in December‐January and SAT in February during 1979–2022 has been observed, that is, a strong (weak) SPV corresponds to a cooling (warming) over Asia. This relationship is independent of the Arctic Oscillation. The influence of the SPV on SAT over Asia cannot be solely explained by radiative processes, but is instead related to circulation anomalies in the troposphere. Specifically, the influence of the SPV on Asian SAT is mediated through the "downward control" mechanism. A strong SPV signal propagates downward to the Atlantic sector, weakening the Northeast Atlantic-East Europe-Asia tripolar teleconnection wave train. This weakens planetary wave propagation from the North Atlantic to Asia, leading to negative geopotential height anomalies and cyclonic circulation anomalies over the region. These circulation anomalies, accompanied by anomalous northerly winds, are beneficial to the colder air transportation from the higher latitudes to Asia, facilitating a surface cooling over Asia. We also found the robust influences of March Arctic stratospheric ozone (ASO) on the differences in the precipitation and evaporation in April over Eastern China. When ASO decreases in March, it tends to result in a higher and colder tropopause in the polar, a stronger subtropical jet stream, an intensified local Hadley circulation accompanied by anomalous downward motion over Eastern China, and consequently, drying in this region, and vice versa. These findings suggest that Arctic stratospheric variability could serve as potential predictors for temperature and precipitation changes in East Asia.
How to cite: Hu, D.: Impacts of stratospheric polar vortex and ozone on surface air temperature and precipitation over Asia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1606, https://doi.org/10.5194/egusphere-egu25-1606, 2025.
Anomalies in the stratospheric polar vortex (SPV), such as sudden stratospheric warming (SSW) events, significantly impact surface weather patterns. While the general influence of SSWs on the troposphere is robust, individual events exhibit large variability, partly due to the substantial difference in dynamics and SPV evolution across events. Understanding the physical processes driving SSWs is therefore essential. In this study, we investigate SPV dynamics, focusing on non-linear coupling between planetary wave modes.
We use potential enstrophy and eddy total energy budget analyses to quantify the contributions of different physical processes to SPV evolution. Applying this framework to both an idealized simulation and reanalysis data of the 2003 SSW event, we find that non-linear wave–wave interactions play a crucial role. In the idealized simulation, wave-2 structures emerge in the stratosphere without a prescribed wave-2 source, attributed to non-linear transfer of enstrophy and energy from wave-1 to wave-2. In the 2003 case study, interactions between wave-1 and wave-2 contribute to the transition from a displacement to a split structure. We also find indications of quasi-linear coupling and upscale enstrophy fluxes from wave-2 to wave-1 during this period.
Our findings highlight the significant impact of non-linear wave–wave interactions in transitioning the SPV between configurations. These complex interactions contribute to the uniqueness of each SSW event and may help explain the variability observed across different SSWs.
How to cite: Rupp, P., Hitchcock, P., and Birner, T.: Coupled planetary wave dynamics in the polar stratosphere analyzed with potential enstrophy and eddy energy budgets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2534, https://doi.org/10.5194/egusphere-egu25-2534, 2025.
In July and August 2024, two rare consecutive stratospheric sudden warming (SSW) events, SW07 and SW08 occurred in the Southern Hemisphere. These events were marked by a rapid Antarctic temperature increase of nearly 17°C at 10 hPa within a few days and a significant deceleration of the stratospheric polar vortex (SPV). In particular, SW07 represents the earliest warming event recorded in the satellite era. Both events meet the criteria for minor SSWs and set new historical temperature records. The analysis reveals that planetary wave anomalies, dominated by nonlinear processes driven by strong tropospheric blocking highs and stratospheric preconditions, played a crucial role in SW07. Additionally, the rapid downward propagation of negative SAM into the troposphere, induced by SW07, created a favorable circulation background for planetary wave perturbations before SW08. These perturbations enhanced ozone transport from low-latitudes ozone to the pole, warming the atmosphere through the absorption of solar shortwave radiation and providing a warm background conducive to triggering SW08.
How to cite: Zi, Y., Long, Z., Sheng, J., Lu, G., Perrie, W., and Xiao, Z.: Rare Sudden Stratosphere Warming Events in the Southern Hemisphere in 2024, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4427, https://doi.org/10.5194/egusphere-egu25-4427, 2025.
Accurate representation of the large-scale stratospheric transport in chemistry-climate models is crucial for interpreting observed variability in chemical species, such as ozone, and making reliable projections regarding future changes. Subtropical transport barriers separate the tropical stratosphere, influenced by slow upwelling, from the surf zones, where rapid mixing occurs due to wave breaking. Long-lived tracer contours reflect the combined effects of advection and mixing and can be used to identify the location of the subtropical transport barriers. This study comprehensively compares tracer- and dynamics-based diagnostics of the subtropical transport barriers in the CESM-WACCM4 chemistry-climate model and various observational datasets. The model tracer-based estimates show excellent agreement with observations regarding seasonal climatology and variability linked to the Quasi-Biennial Oscillation (QBO). The chemical boundaries shift due to the secondary meridional circulation induced by the QBO in the winter hemisphere and due to the enhanced isentropic mixing associated with waves crossing the equator in the summer hemisphere. Consistent with previous studies, the observational tracer metrics feature a southward shift of the tropical pipe over 2005–2012. The model, which nudges the QBO to observations, captures qualitatively the shift over this period. Dynamical metrics represent individual transport processes and thus fail to capture the variability and trends in the tracer-based boundaries.
How to cite: Ivaniha, O., Abalos, M., Calvo, N., Stiller, G., Shah, K., and Davis, S.: Stratospheric subtropical transport barriers in CESM-WACCM and observations: climatology, variability, and trends, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12487, https://doi.org/10.5194/egusphere-egu25-12487, 2025.
The stratospheric dynamics and associated extremes, such as sudden stratospheric warmings (SSWs) and the formation of polar stratospheric clouds (PSCs), exhibit a pronounced interhemispheric asymmetry. SSWs are exceedingly rare in the Antarctic, while the extreme cooling conditions required for the formation of water-based PSCs (Type II) are infrequent and short-lived in the Arctic. To investigate the drivers of this asymmetry, we conducted a series of semi-idealized model experiments, progressing from aqua-planet configurations mimicking Southern Hemisphere (SH) conditions to more realistic Northern Hemisphere (NH) setups.
Our results reveal that orography and land-sea thermal contrast (LSCO) alone cannot fully explain the observed interhemispheric asymmetry. Crucially, midlatitude oceanic sea surface temperature (SST) fronts, associated with western boundary currents, play a pivotal role in aligning stratospheric dynamics and extremes with NH-like conditions. Similar to LSCO, SST fronts significantly enhance the stratospheric convergence of planetary wave activity, which strengthens the Brewer-Dobson Circulation. This leads to substantial increases in high-latitude adiabatic warming, elevating the frequency of Arctic SSWs while simultaneously suppressing conditions conducive to PSC formation. These findings highlight the critical yet underexplored role of oceanic SST fronts in shaping the interhemispheric differences in stratospheric dynamics and extremes.
How to cite: Omrani, N.-E., Keenlyside, N., Nakanura, H., Ogawa, F., and Lubis, S.: Role of Oceanic SST Fronts in the Interhemispheric Asymmetry of Stratospheric Dynamics and Associated Extremes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20115, https://doi.org/10.5194/egusphere-egu25-20115, 2025.
How to cite: Kerzenmacher, T., Braesicke, P., Grabowski, U., and Stiller, G.: Using MIPAS Tracer Measurements to Investigate the Quasi-Biennial Oscillation and Mean Meridional Circulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13230, https://doi.org/10.5194/egusphere-egu25-13230, 2025.
How to cite: Bremaud, V., Podglajen, A., Hertzog, A., and Plougonven, R.: An idealized two-dimensional modelling framework to simulate QBO-like oscillations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11644, https://doi.org/10.5194/egusphere-egu25-11644, 2025.
Sudden stratospheric warmings (SSWs) can significantly impact tropospheric weather systems. Previous studies suggest that SSWs may also influence stratosphere-to-troposphere transport (STT), but their spatial and temporal distribution and mechanisms are not fully understood. The complex relationships between SSWs and the El Niño-Southern Oscillation (ENSO) have also made it difficult to isolate the effects of SSWs on STT. From an idealized ENSO simulation with the WACCM4 model using a stratospheric origin ozone tracer, we investigate the effect of SSWs on the STT of ozone under different ENSO phases. We find a significant increase in lower tropospheric ozone from the SSW onset up to 3 months later over the Arctic, North America, and Europe, regardless of the ENSO phase. This study highlights the significant influence of SSWs on STT on a subseasonal scale. Our results also emphasize the need to consider SSWs when addressing the ENSO impact on STT.
How to cite: Lee, J., Butler, A., Albers, J., Wu, Y., and Lee, S.: Impact of Sudden Stratospheric Warmings on the Stratosphere-to-Troposphere Transport of Ozone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3360, https://doi.org/10.5194/egusphere-egu25-3360, 2025.
Global chemical transport models often overestimate stratospheric methane concentrations due to inaccuracies in simulating stratospheric circulation. If uncorrected, these biases can distort inverse analyses of satellite methane column observations (e.g., GOSAT), which encompass contributions from both the troposphere and stratosphere, and lead to erroneous estimates of surface emissions and tropospheric sinks. In this study, we assess the impact of stratospheric biases on the global inversion of satellite column observations. We implemented several correction methods, including empirically derived polynomial corrections, age-of-air proxies, and both offline and online replacements of stratospheric methane fields with independent observations. Correcting for stratospheric biases on average resulted in a 22 Tg a-1 increase in inferred global methane emissions from GOSAT data, with notable latitudinal shifts. The correction increased extratropical emissions by 46 Tg a-1 but decreased tropical emissions by 24 Tg a-1. Different correction methods varied in their impact on the inversion estimates of emissions and OH concentrations, underscoring uncertainties in bias correction. Our results also indicate that stratospheric biases can induce tropospheric biases in the simulation through stratosphere-troposphere exchange, potentially affecting the analysis of surface methane observations.
How to cite: Zhang, P., Zhang, Y., and liang, R.: Correction of simulation biases in stratospheric methane concentrations for the inverse analysis of satellite column observations , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1327, https://doi.org/10.5194/egusphere-egu25-1327, 2025.
Posters on site: Thu, 1 May, 08:30–10:15 | Hall X5
Sudden stratosphere warming (SSW) is a distinctive phenomenon characteristic of the winter stratospheric circulation. SSW is linked to the activity of planetary waves. Planetary waves are one of the most prominent waves in the stratosphere, and their evolution, propagation, and anomalies are critical scientific issues in atmospheric dynamics. This study primarily investigates the persistent trend changes in planetary waves and SSW-related climate indices within the stratosphere. Analyzing these trends to enhance the prediction of stratospheric atmospheric evolution. We conducted a zonal harmonic analysis using the potential height fields from ERA5, MERRA-2, and MLS satellite data to determine the amplitudes of planetary waves with wave numbers 1 to 3, analyzing a time period covers 40 winter-spring seasons in the Northern Hemisphere. Climatology for the last four decades allows us to reliably determine the average indicators that characterize zonal waves 1 – 3 during 4 months (December – March) in the stratosphere and lower mesosphere. We are looking for signs and possibilities of the SSW prediction by analyzing the trends of anomalous changes in planetary wave activity. We also discuss the trend changes in climate indices associated with stratospheric atmospheric dynamics, mainly focusing on El Nino Southern Oscillation, Arctic Oscillation, Equivalent Effective Stratospheric Chlorine, Quasi-Biennial Oscillation and NH Coupled Mode Index, over the 40 winter and spring season in the Northern Hemisphere from 1980 to 2023. We investigate the possible connections between these indices and SSW events to identify potential precursors associated with SSW. We try to find appropriate parameters that can trigger SSW. Therefore, the analysis of planetary wave parameters and climate indices can provide insights into SSW events' frequency and dynamic characteristics.
How to cite: Yu, R., Ivaniha, O., Shi, Y., Evtushevsky, O., Milinevsky, G., Grytsai, A., Klekociuk, A., and Wang, X.: Long-term changes in planetary wave and SSW parameters in the Northern Hemisphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7938, https://doi.org/10.5194/egusphere-egu25-7938, 2025.
Gravity waves contribute to the energy and momentum transport and budget in the atmosphere, in the stratosphere in particular. Observations and simulations of their effects poses significant challenges due to diverse spatial and temporal scales involved. Despite these challenges, incorporating the effects of gravity waves is essential for global climate and weather prediction models. This study presents a first climatological analysis of resolved gravity waves based on the ECMWF's ERA5 reanalysis and their impacts on the mean flow over more than 43 years. The spatiotemporal distribution of the gravity wave drag is investigated, short and long-term variability analysed locally above the hotspots and in a zonal mean. The results match very well the theoretically assumed properties of gravity waves in the atmosphere, which is very encouraging with respect to the question, how realistic are resolved gravity waves in reanalyses. Our research enhances our understanding of gravity wave drag in the stratosphere and can be used for informing and validating the gravity wave parameterization schemes in climate models.
How to cite: Šácha, P., Procházková, Z., and Zajíček, R.: Quasi-observational climatology of the gravity wave forcing in the stratosphere., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9214, https://doi.org/10.5194/egusphere-egu25-9214, 2025.
Stratospheric sudden warmings and other polar vortex events have well-documented impacts on winter surface weather and climate over middle to high latitudes. However, the scientific understanding of the influence of the polar stratosphere on the tropics remains in its early stages. There are two primary pathways through which these influences can occur. In the first pathway, polar vortex events modulate the strength of the Brewer-Dobson circulation, affecting both the tropical stratosphere and troposphere. In the second pathway, the dynamical downward coupling from the stratosphere into the extratropical troposphere may also influence the tropical troposphere. To investigate the type and magnitude of tropical impacts from polar vortex events, we employ a composite analysis of ERA5 reanalysis data spanning from 1957 to 2024. Our findings reveal that stratosphere-related changes in the Brewer-Dobson circulation not only affect the tropics but also extend into the subtropics and extratropics of the opposite hemisphere. These impacts manifest in various variables, including tropical upwelling, the descent rate of the Quasi-Biennial-Oscillation, tropical stratospheric water vapor, the height and temperature of the tropical tropopause, and tropical column ozone. Furthermore, we find that stratospheric circulation events are associated with shifts in the poleward extent of the tropical Hadley cell. While these tropical changes are generally weaker compared to those observed at higher latitudes, they are nonetheless of comparable duration and statistically significant.
How to cite: Reichler, T. and Wu, Z.: Tropical Impacts From Polar Vortex Events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13831, https://doi.org/10.5194/egusphere-egu25-13831, 2025.
Stratospheric variability can significantly impact the tropospheric circulation and influence surface weather conditions. While many studies have established links between changes in the stratospheric polar vortex strength or the downward reflection of Rossby waves and modulations of the mid-latitude tropospheric circulation, challenges remain in developing quantitative approaches to explore these interactions systematically. Addressing this gap, we propose applying quantile generalized additive models (QGAMs) to statistically explore the connections between stratospheric variability, tropospheric circulation patterns and 2-m temperatures.
This study focuses on the North Pacific and North America, regions where stratospheric processes are known to modulate tropospheric circulation patterns and surface extremes. While the lower quantiles of 2-m temperatures are predominantly governed by tropospheric weather regimes, incorporating stratospheric information can further improve the representation of cold temperatures in some regions of North America at time lags of about two weeks. Given the potential of the stratosphere as an additional predictor for North American cold spells, we further investigate the statistical link between stratospheric dynamics and North American weather regimes.
By providing new insights into stratosphere-troposphere coupling mechanisms we can improve our understanding of the large-scale circulation features driving cold spells and other surface weather extremes. This approach has important implications for advancing their predictability on sub-seasonal to seasonal timescales, potentially informing more effective early-warning systems.
How to cite: Schutte, M., Messori, G., and Olivetti, L.: Stratosphere-Troposphere Dynamics and North American Cold Spells: A Quantile Generalized Additive Approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7908, https://doi.org/10.5194/egusphere-egu25-7908, 2025.
Recent research is highlighting the importance of the stratosphere and stratosphere-troposphere coupling for subseasonal-to-seasonal prediction of the winter North Atlantic Oscillation (NAO), the dominant mode of variability in the Northern Hemisphere.
Collingwood et al 2024 demonstrated the relevance of the October upper stratosphere to polar vortex development and predictability of winter NAO. They found that anomalous meridional wind in the upper stratospheric “surf zone”, resulting primarily from anomalous eddy momentum flux convergence, generates a signal that propagates down and impacts the vortex and surface NAO, with correlation coefficients of r=0.36 and 0.40 respectively.
Further investigation finds that the relevance of this upper stratospheric meridional wind to winter NAO is not limited to October, but extends to the preceding summer too. This study seeks to better understand the curious mechanisms dictating this teleconnection as well as its decadal variability.
How to cite: Collingwood, L., Scaife, A., Sinha, B., Marsh, R., Marshall, G., and King, J.: On the predictive value of upper stratosphere dynamics for winter NAO, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10722, https://doi.org/10.5194/egusphere-egu25-10722, 2025.
How to cite: Nangombe, S. and Domeisen, D.: Stratospheric drivers of precipitation and temperature in southern Africa, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12791, https://doi.org/10.5194/egusphere-egu25-12791, 2025.
Posters virtual: Tue, 29 Apr, 14:00–15:45 | vPoster spot 5
EGU25-7147 | ECS | Posters virtual | VPS2
An Enigmatic Variability in the Tropical Middle AtmosphereTue, 29 Apr, 14:00–15:45 (CEST) | vP5.13
The tropical middle atmosphere is characterized by long-period oscillations such as the Quasi Biennial Oscillation and the Semiannual Oscillation which are primarily driven by the interaction of a broad spectrum of atmospheric waves with the background flow. Using reanalysis datasets and independent rocket soundings from a low latitude location, we identified a hitherto unreported variability in the tropical middle atmosphere that appears at a variable interval of 2-5 years in the late 20th century and 7-9 years in the early 21st century. The newly identified variability, Quasi-Periodic Easterly Bursts (QPEBs) as we call them, manifests as enhanced easterlies during the easterly phase of the Stratopause Semiannual Oscillation around May-July. QPEBs are found to have remote influences on the Southern Hemispheric polar vortex as well as residual circulation in the lower mesosphere. A momentum budget analysis reveals that QPEBs are found to be primarily caused by enhanced cross-equatorial advection as well as gravity wave drag. Even though a close association with the Quasi Biennial Oscillation winds is observed, the cause of the observed periodicity remains elusive.
How to cite: Koushik, N. and Kumar, K. K.: An Enigmatic Variability in the Tropical Middle Atmosphere, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7147, https://doi.org/10.5194/egusphere-egu25-7147, 2025.
EGU25-5045 | Posters virtual | VPS2
Ozone anomalies over Eastern and Western Hemisphere Antarctic stations during sudden stratospheric warming life cycleTue, 29 Apr, 14:00–15:45 (CEST) | vP5.30
Sudden stratospheric warming (SSW), a well-known phenomenon in the polar atmosphere, changes the distribution of various atmospheric parameters due to the enhanced activity of planetary waves. These processes produce zonal asymmetry in total ozone content (TOC) with a wave-1 pattern. However, regional characteristic properties of the Antarctic TOC anomalies that occur during the SSW life cycle have not been studied in detail. We aim to analyze the connection of zonally asymmetric variations of TOC with SSW events. The analysis is based on a time series of ten research stations in the Antarctic region and gridded fields from MSR-2 TOC data. Here, we compare the evolution of TOC and wave amplitudes in three Southern Hemisphere SSW events. The TOC time series over ten stations in the Antarctic region and superposed epoch analysis for ±60-day time lags relative to the SSW central date were used. A regional division according to the geographic location of the stations and TOC climatology was introduced. According to the TOC asymmetry pattern, a division between Eastern and Western Hemisphere stations is used. We observe zonally asymmetric ozone responses in the two hemispheres during the SSW life cycle, including distinct precursor properties before the SSW onset. This research clarifies the different SSW properties in local ozone observations under the zonally asymmetric TOC field. The previously unknown regional manifestations of Antarctic TOC anomalies in the early stage of the SSW are discussed. The role of wave-1 and the zonally asymmetric Brewer-Dobson circulation in the Eastern–Western Hemisphere difference in the Antarctic TOC variability is also discussed. We also characterize total ozone levels in the years immediately preceding and following the three most significant SSW events. We examine the influence of planetary wave activity and large-scale climate modes on the level of interannual ozone variability and its regional patterns. There is evidence that Antarctic total ozone in the years adjacent to these SSW events is reduced, which may serve as a precursor signal of these events and an indicator of their longer-lasting influence. We discuss the implications and importance of these ozone perturbations for the regional Antarctic climate.
How to cite: Milinevsky, G., Yu, R., Grytsai, A., Evtushevsky, O., Klekociuk, A., and Ivaniha, O.: Ozone anomalies over Eastern and Western Hemisphere Antarctic stations during sudden stratospheric warming life cycle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5045, https://doi.org/10.5194/egusphere-egu25-5045, 2025.
