We welcome contributions that explore:
- The links between large-scale atmospheric circulation features (e.g., circulation patterns, weather regimes, blocking patterns, extra-tropical cyclones, teleconnection indices, NAO) and various types of regional extreme weather events (such as heat waves, heavy precipitation, floods, droughts)
- Past, recent and future trends in frequency, intensity, and variability of regional extremes or surface environmental variables and their associated atmospheric features under climate change
- The influence of internal climate variability on the occurrence of regional extreme events associated with large-scale atmospheric circulation features
- The use of innovative methods, including large ensembles, and AI for circulation type classification
This session invites contributions that explore the connections between different types of regional extremes and the atmospheric circulation, as well as studies from general synoptic climatology that focus on the relationship between atmospheric circulation dynamics and near surface environmental variables, their variability, and changes. The aim is to enhance our understanding of the dynamic drivers behind regional extremes in the context of climate change.
Over the last few decades, Europe has emerged as a hotspot for heatwaves (HWs), with prominent examples such as 2003, 2010, 2018 and 2022. The development of European HWs is often linked to atmospheric blocking, in summer most notably in the form of a so-called Omega blocking. However, not all HWs necessitate atmospheric blocking, particularly over Southern and Central Europe, where they can also be caused by poleward extensions of the subtropical high pressure belt, so-called subtropical ridges. These can be positioned such that they induce southward flow anomalies of hot and dry air, which have been suggested before as an explanation of the overproportional increase in heat extremes over Europe.
Future projections show a clear increase in the number and intensity of HWs but are inconclusive with respect to changes in atmospheric blocking. Moreover, subtropical ridges are generally not considered, although they may play a greater role in a warmer climate. We present ongoing research into CMIP6-projected changes of both Omega (and other) atmospheric blocking and subtropical ridges for Europe. Besides overall trends, we are particularly interested in the most intense and most persistent HWs and whether their link to large-scale atmospheric flow anomalies such as Omega blocking or ridges might change.
Preliminary results based on two large ensembles (SMILEs; MPI-GE and SMHI-LENS) suggest that subtropical ridges are projected to increase in frequency during summer in Western and Central Europe, while for Omega and other atmospheric blocking a small reduction or no change is identified. Particularly during HWs, the frequency of ridge detection increases substantially for a warmer climate in both ensembles. This is of particular interest as such ridge-type HWs are generally found to more intense (albeit not more persistent) than Omega-type HWs, both in the present and the projected future climate.
How to cite: Lemburg, A., Fink, A. H., Lima, M. M., and Pinto, J. G.: Projected future changes in Omega blocking and subtropical ridges and their relationship to European heatwaves in two SMILEs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12518, https://doi.org/10.5194/egusphere-egu26-12518, 2026.
Impactful midlatitude heatwaves are often triggered by persistent anticyclonic atmospheric blocks. Objectively defining such impactful blocking circulations remains a challenge for climate impacts analysis and theoretical understanding, which this work seeks to address. Here, persistent midtropospheric anticyclones over the entire northern hemisphere midlatitude region that lead to anomalously warm surface conditions are identified, independently of specific blocking metrics, with a two-step identification method. This method’s input is daily boreal-summer midtropospheric geopotential height, from reanalysis or from earth-system models (ESMs), over a circumglobal set of midlatitude domains spanning about longitude and latitude. The method’s output is a set of days featuring persistent states that reflect the predominant flow pattern, Archetype 1, extracted using Archetype Analysis. Persistence is defined by high values of a persistence metric, symbolized θ-1, that reflects how long the atmosphere tends to stay near a specific atmospheric configuration. The high θ-1 Archetype 1 is a barotropic anticyclonic block with warm surface conditions, lasting about a week. Extending previous European-domain persistence analysis, the archetype analysis filters out less-impactful persistent cyclonic systems associated with anomalously cold conditions. Over land regions, heatwaves are 5-10 times more frequent under persistent Archetype 1 conditions than in the record as a whole. Persistent Archetype 1 patterns are realistically represented in historical ESM simulations. There is a regional increase of θ-1 by the end of the century, which can signify a continuation of recent trends of the weakening of the boreal summer circulation. Archetype 1 persistent events spatial structure does not change by the end of the century, but their persistence increases by about 7% as part of the overall θ-1 increase, which can signify that they are getting longer as a result of climate change.
How to cite: Vakrat, E. and Kushner, P.: Robust Identification of Impactful Boreal Summer Anticyclones and Implications for Future Climate , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4093, https://doi.org/10.5194/egusphere-egu26-4093, 2026.
Global warming is evident in the extreme events (XE) of daily maximum temperature (Tx) in the Iberian Peninsula, but this behaviour is not fully explained by the mean evolution of temperature, Castillo-Mateo et al (2025). In this context, it is clear that projections of XE risk are required for future climates, and they must be obtained using methods specifically designed for extremes.
This work proposes a new statistical tool to obtain daily and local-scale projections for the occurrence of XE, defined as days with Tx above a pre-established threshold. First, the tool relies on a geostatistical model that links the occurrence of XE at each point of the study region with atmospheric covariates at different geopotential levels, taken from grid points in a surrounding area. Second, a selection of AR6 GCM trajectories is performed using criteria that account for (1) the reproduction of the daily frequency and persistence of weather types over the region, and (2) the reproduction of the empirical distribution of ERA atmospheric variables at the daily scale. Third, the projected values of the atmospheric covariates are used as inputs for the statistical model, allowing estimations of daily characteristics at both local and regional scales.
Model estimation is carried out using daily Tx data for 1960--2024 from 36 Spanish stations (European Climate Assessment& Dataset), for June-August. XE is defined by the 95th percentile of Tx for 1991--2020. Covariates consist of geopotential variables at 12 p.m. for pressure levels of 500 and 700 hPa, on a 1º x1º grid over the area 45º--35º N and 10ºW--5ºE, obtained from the ERA5 reanalysis. The statistical models achieve high goodness-of-fit, with AUC values above 0.8 for validation conditions at most stations.
Trajectories from 36 AR6 GCMs are analysed to select those that meet the criteria, and only six trajectories remain. Finally, projections for 2031--2060 are obtained for the Iberian Peninsula under different scenarios.
References
Castillo-Mateo, J., Gelfand, A.E., Gracia-Tabuenca, Z., Asín, J., Cebrián, A. C. (2025). Spatio-temporal modeling for record-breaking temperature events in Spain. Journal of the American Statistical Association, 120, 645-657.
How to cite: Barrio, E., Gracia-Tabuenca, Z., Asín, J., and Cebrián, A. C.: Projecting Daily Extreme Heat Events in the Iberian Peninsula using Statistical Downscaling with 700, 500 and 300 Geopotential Fields, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1370, https://doi.org/10.5194/egusphere-egu26-1370, 2026.
Hot days gain great attention around the world for their wide impacts on water resources, agriculture, society productivity, biosystems, and public health. We explore daily data from weather stations, the global surface summary of day product produced by the National Centers for Environmental Information of the United States, to determine changes in the monthly frequency of hot days (maximum daily temperature above 35 degrees Celsius) in Western, Central, and Eastern Europe. The monthly percentages show increasing trends in June, July, and August between 1973 and 2024. They are positively correlated with the monthly average geopotential height at 500hPa: Correlation coefficients computed with monthly ERA5 reanalysis data over the three regions lie between 0.54 and 0.78 (p<0.01). We further investigate the impact of anthropogenic global warming and internal climate modes such as the Pacific Decadal Oscillation (PDO) and El Niño-Southern Oscillation (ENSO) using geopotential height at 500 hPa and the surface air temperature (SAT) from ERA5. We draw on results for the three regions based on a decomposition method, Cyclo-Stationary Empirical Orthogonal Functions. We illustrate the method for two exemplary time points: July 1976, for which the hot days percentage was the least (1.3%), and July 2024, for which the percentage was the most (16.3%) in the considered areas. As expected, the anthropogenic global warming contributed to an increase in SAT between the two example months. By contrast, PDO statistically contributed to slightly lower SAT in July 2024 but slightly higher SAT in July 1976. Similarly, the ENSO mode played a small positive (negative) role in SAT in the West, Central Europe, but a slightly negative (positive) role in Eastern Europe in July 1976 (2024). In all three modes, the geopotential height positive and negative anomalies are consistent with those in SAT. Positive anomalies in geopotential height are usually accompanied by subsidence and strong solar irradiance at the surface, and therefore favor SAT increase, and vice versa. Regressing the anthropogenic global warming mode on SAT in Europe for the five July months with the most (in 2024, 2007, 2015, 2012, 2023) and the least hot days percentages (in 1976, 1992, 1979, 1986, 1989), clearly shows a positive impact for the former and a negative contribution for the latter, except 1989. We test the robustness of our results by comparison to a second method, Low-Frequency Component Analysis. Our results will enhance the understanding of the influence of forced and internal climate variability, specifically, modes of variability, on the frequency of hot days in the mid-latitudes.
How to cite: Li, Y., Baudouin, J.-P., and Rehfeld, K.: Variability of Hot Days in the Middle Latitudes of Europe between 1973 and 2024, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9731, https://doi.org/10.5194/egusphere-egu26-9731, 2026.
Wildfires in Eastern Siberia have intensified rapidly in recent decades, with increasing impacts on air quality and Earth’s climate. This intensification is closely linked to rising fire weather risk, as indicated by vapor pressure deficit (VPD), which is jointly modulated by large-scale circulation and land–atmosphere coupling, yet their respective contributions remain poorly quantified. Here we attribute the 2004–2024 summer VPD trend over Eastern Siberia using the circulation and soil moisture analogue methods. Observations show a pronounced VPD increase of 0.67 hPa decade⁻¹, which is primarily associated with variations in atmospheric circulation that contribute 0.41 hPa decade⁻¹, while the soil-moisture-related land contribution reaches 0.38 hPa decade⁻¹. These two contributions are not independent, reflecting a coupled pathway of circulation-induced land feedbacks, estimated at ~0.20 hPa decade⁻¹. CMIP6 simulations further confirm the robustness of this mechanism, showing that land–atmosphere coupling amplifies the circulation-driven VPD trend. The dominant circulation anomalies are associated with warm sea surface temperature (SST) anomalies over the Barents Sea, which excite a Rossby wave train across high-latitude Eurasia and favor subsidence, suppressed precipitation, and reduced near-surface relative humidity, thereby elevating VPD. Circulation-induced soil drying, likely related to precipitation suppression, further enhances atmospheric dryness by altering surface energy partitioning and increasing net radiation. Together, these results show that recent fire-weather risk intensification in Eastern Siberia is primarily controlled by atmospheric circulation, with substantial amplification by circulation-triggered land–atmosphere feedbacks.
How to cite: Bai, D. and Yu, H.: Quantifying the contributions of atmospheric circulation and land–atmosphere coupling to the rapid increase in fire weather risk over Eastern Siberia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4646, https://doi.org/10.5194/egusphere-egu26-4646, 2026.
This work investigates the connection between large-scale atmospheric dynamics in the North Atlantic and winter temperature variability by analyzing the contribution of weather regimes to the occurrence of daytime and nighttime cold and warm events in Northwest Africa, focusing on Morocco.
Weather regimes are first identified using a conventional circulation-based framework relying on k-means clustering of geopotential height anomalies. The sensitivity of the inferred circulation–temperature relationships to the choice of regime identification method is then investigated by comparing classical geopotential-based regimes with classifications incorporating jet-stream information and with non-linear regimes derived from variational autoencoders. This analysis is intended to evaluate the robustness and impact relevance of weather regimes for winter temperature extremes in Morocco.
For daytime temperatures, warm winter days are generally associated with a Greenland Anticyclone (NAO−) configuration across most of Morocco, while the zonal regime (NAO+) exhibits a marked inland–coastal contrast, with warmer conditions inland. In contrast, Blocking (BL) and Atlantic Ridge (AR) regimes are more likely to lead to cold daytime events. The AR regime, in particular, shows a dominant influence, accounting for more than 80% of cold daytime events, especially in northern and coastal regions. For nighttime temperatures, the AR regime clearly favors cold outbreaks over the entire country, whereas NAO− conditions strongly enhance the occurrence of warm winter nights. These relationships can be physically interpreted in terms of large-scale warm and cold air mass advection from the Atlantic, with an additional contribution from local radiative warming or cooling under anticyclonic and cyclonic conditions. The intersections and differences between the above-mentioned methods are also analyzed in terms of correlations with the four extremes in addition to weather regime structure.
How to cite: Balhane, S., Driouech, F., El Ouaraini, R., El Aabaribaoune, M., and Zerouaoui, H.: From Linear Clustering to Deep Learning: Assessing Weather Regimes’ Impacts on Winter Extreme Temperatures over Northwestern Africa with a Focus on Morocco., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18823, https://doi.org/10.5194/egusphere-egu26-18823, 2026.
In recent decades, Eurasia has experienced a substantial increase in cold extremes. While the North Atlantic Oscillation (NAO) is well established as a modulater of Eurasian cold extremes, we uncovered a previously overlooked, yet increasingly critical, driver in a warming climate—the Barents Oscillation (BO). With accelerated Arctic warming, the BO has emerged as a dominant atmospheric circulation pattern. This intensified BO accounts for 59% of the observed severe cold extremes across Eurasia. In the future during 2015−2100, the BO is projected to intensify across SSP scenarios, with its increasing rate in SSP5-8.5 doubling that of SSP1-2.6. The enhanced BO is expected to exacerbate cold extremes by approximately −0.5°C for each standard deviation increase in the BO intensity. These findings emphasize the BO’s growing importance in amplifying Eurasian cold extremes under global warming, challenging the prevailing NAO-centric framework.
How to cite: Wang, H.: Regime Shift in a Warming Climate—Emerging Barents Oscillation and its Dominance in Eurasian Cold Extremes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3332, https://doi.org/10.5194/egusphere-egu26-3332, 2026.
Midlatitude cold spells (CSs) are often associated with disruptions to transportation and energy infrastructures and increased risk to life and livelihoods. While the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR6 2021) assessed that CSs have become less frequent across most land areas due to human caused climate change, some studies suggest that their frequency may not be declining everywhere.
In this work, we investigate Northern Hemisphere trends of CS characteristics in reanalysis data since the winter 1980-81, using a novel spatio-temporal CS tracking algorithm based on daily 2m temperature anomalies (Osmolska et al., 2025). We analyse the changes in frequency, severity, duration and area of CSs identified using raw and detrended temperature data to disentangle the effects of mean background warming (thermodynamics) versus circulation changes (dynamics).
We show that in the Northern Hemisphere, the average winter frequency of CSs decreases due to background warming at a rate of 19 days decade-1, with similar trends in North America, Europe and East Asia. These regions are also experiencing less severe CSs, with the average 5th percentile temperature threshold in the Northern Hemisphere increasing by 0.3 K decade-1. We find that the decline in the cumulative annual area occupied by CSs is mainly due to the decrease in frequency, with the area decrease being equal to 1x108 km2 per decade. Finally, we also show that the average duration of CSs has significantly decreased in northern North America (-1.3 days decade-1) and southern Europe (-1.0 days decade-1).
When dynamical effects are considered alongside the thermodynamical effects, we show that dynamical variability contributes to CS becoming less frequent in the Northern Hemisphere (-2.9 days decade-1), and contributes to a decreasing persistence and cumulative CS area over northern North America. In all other regions, we found minimal change in CS characteristics from circulation changes.
In this work, we demonstrate that the rise in mean temperature is the primary driver of recent Northern Hemisphere CS trends; however, changes in dynamical variability have contributed to regional reductions in CSs in northern North America in contrast to some studies which have suggested circulation changes have enhanced CSs there.
How to cite: Osmolska, W., Maycock, A., and Chemel, C.: Trends in Northern Hemisphere cold spells across the winter periods 1980/81-2024/25, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8303, https://doi.org/10.5194/egusphere-egu26-8303, 2026.
Storm Éowyn made landfall in the British Isles on 24 January 2025, becoming one of the most devastating extratropical cyclones in recent years with average wind speeds exceeding 39 m/s. This storm, following record-breaking low temperatures and snowfall in the Southern United States, constitutes a Pan-Atlantic cold and windy compound extreme. Given the widespread impacts of these compound extremes, identifying their atmospheric precursors is critical for improving predictability and preparedness.
The stratosphere played an important role in the January 2025 Pan-Atlantic event. We demonstrate how a strong stratospheric polar vortex, in conjunction with tropospheric drivers like the Alaskan Ridge weather regime, facilitated enhanced southward cold air advection in North America and the intensification of cyclone Éowyn over the North Atlantic. This case study provides an archetype for future compound Pan-Atlantic cold-windy events and outlines possible pathways for improved sub-seasonal forecasting.
How to cite: Strigunova, I., Schutte, M., and Messori, G.: Role of the stratosphere in the January 2025 Pan-Atlantic Event: A Case Study of Storm Éowyn, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5678, https://doi.org/10.5194/egusphere-egu26-5678, 2026.
Based on the observational hourly precipitation data and the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis 5 (ERA5) products from 2006 to 2020, 22 rainstorm processes in the eastern foot of Helan Mountain are objectively classified through the hierarchical clustering method, and the circulation characteristics of different patterns are comparatively analyzed in this study. The results show that the occurrences of rainstorm processes in the eastern foot of Helan Mountain are most closely related to three circulation patterns. Patterns I and III mainly occur in July and August, with similar zonal circulations in synoptic backgrounds. Specifically, the South Asia high and the western Pacific subtropical high are stronger and more northward than in normal years. The frontal systems in westerlies are inactive, while the water vapor from the ocean surface in the south is mainly transported to the rainstorm area by the southerly jet stream at 700 hPa. The dynamic lifting anomalies are relatively weak, the instability of atmospheric stratification is anomalously strong, and thus the localized severe convective rainstorm is more significant. Comparatively, rainstorm processes of pattern I are accompanied by stronger and deeper ascending motions, and the warm-sector rainstorm is more extreme. Pattern III shows a stronger and deeper convective instability, accompanied by larger low-level moisture. Rainstorm processes of pattern II mainly occur in the early summer and early autumn, presenting a meridional circulation pattern of high in the east and low in the west in terms of geopotential height. Besides, the two low-level jets transporting the water vapor northward from the eastern ocean encounter with the frontal systems in westerlies, which makes the ascending motion in pattern II anomalously strong and deep. The relatively weak instability of atmospheric stratification causes weak convection and long-lasting precipitation formed by the confluence of cold air and warm air. This study is helpful to improve the forecasting ability of rainstorm in arid regions.
How to cite: Chen, Y. and Li, A.: Circulations and Thermodynamic Characteristics of Different Patterns of Rainstorm Processes in the Eastern Foot of Helan Mountain, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2163, https://doi.org/10.5194/egusphere-egu26-2163, 2026.
Extratropical cyclones are important modulators of extreme weather in the midlatitudes, with impacts ranging from sub-hourly to seasonal time scales. On seasonal time scales, the aggregation of cyclones in specific regions can lead to anomalous storm track configurations, inducing a seasonal clustering of surface weather extremes with significant societal impacts. Notable examples include the southward shifted storm track associated with the exceptionally negative North Atlantic Oscillation during winter 2009/2010 and the exceptionally stormy winter of 2013/2014 over the British Isles and Ireland. While the role of anomalous storm tracks is often discussed in case studies of extreme seasons, a systematic identification and characterization of extreme seasonal configurations of the extratropical storm tracks is lacking.
We use eddy kinetic energy at 850 hPa to identify anomalous extratropical storm track seasons – referred to as storm track extremes – in the ERA5 reanalysis and explore their characteristics. Using a cyclone-tracking algorithm, we show that storm track extremes are generally induced by both changes in regional cyclone frequency and shifts in the mean intensity of these cyclones. We then assess the role of the El Niño–Southern Oscillation (ENSO) by examining the occurrence of storm track extremes across different ENSO phases and regions. Finally, we investigate how seasonal storm track extremes are linked to surface weather by assessing the frequency of daily precipitation and wind extremes during extreme storm track seasons and how they are related to individual extratropical cyclones. Our work presents the first systematic identification of anomalous storm track seasons and a multi-scale analysis of cyclone-related extremes, highlighting the role of cyclones in shaping seasonal variability and anomalous configurations of storm tracks.
How to cite: Carrard, T., Binder, H., Hauser, S., Voigt, S., and Wernli, H.: Extreme storm track seasons and their influence on wind and precipitation extremes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3311, https://doi.org/10.5194/egusphere-egu26-3311, 2026.
On 29 October 2024, Valencia experienced one of the most catastrophic flood events in Spain’s recorded history, resulting in 232 deaths and widespread damage to infrastructure and property. This event raised urgent questions in science and society on the atmospheric processes that led to this extreme event and the influence of climate change in shaping its severity. The purpose of this study is twofold. First, using observation-based datasets, we investigate the large-to-local scale atmospheric processes leading to this extreme event. Second, using pseudo-global warming simulations with the Weather Research and Forecasting (WRF) model, we quantify the influence of climate change on this extreme event and determine how similar events may unfold in the future.
By identifying and tracking potential vorticity (PV) streamers and cut-off lows as 3-dimensional objects in ERA5, we show that this extreme event resulted from Rossby wave breaking over the North Atlantic nearly a week prior to the event. The cut-off low moved southwards and persisted over northwest Africa and the Iberian Peninsula for four consecutive days. The cyclonic circulation associated with this cut-off low initiated and sustained the transport of warm and moist air masses towards the eastern coast of Spain, generating favorable conditions for deep moist convection.
Present-day WRF simulations generally reproduce the extreme precipitation event well, despite a shift in its location and an underestimation of the highest rainfall amounts as observed at some stations. The consistency of simulated heavy precipitation across different initialization times further supports the robustness of the model results. While spatially aggregated daily precipitation amounts show little sensitivity across pre-industrial, present-day, and future scenarios, the most extreme sub-hourly precipitation intensities systematically increase with warming levels. Therefore, our findings suggest that flood events similar to the October 2024 Valencia flood are likely to recur under future climate conditions with comparable or greater short-duration precipitation intensity, underscoring the need for improved early warning systems and flood risk management.
How to cite: Koukoula, M., de Vries, A.-J., and Torelló Sentelles, H.: Atmospheric drivers and climate change attribution of the October 2024 Valencia flooding , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21515, https://doi.org/10.5194/egusphere-egu26-21515, 2026.
The NAO’s correlation with precipitation in Norway and the Iberian Peninsula is well established, yet its explanatory power diminishes across much of Europe. Other patterns may drive precipitation variability in these regions, but traditional methods for identifying circulation-precipitation relationships have limitations. Prescribed indices assume a causal link between specific sites and physically coherent structures, whereas EOF methods impose linearity and orthogonality constraints that atmospheric circulation does not obey. This study identifies weather regimes associated with precipitation extremes across representative European regions using a non-linear, non-orthogonal, data-driven approach.
Specifically, we employ a machine learning approach that discovers weather regimes directly from mean sea level pressure fields, without prescribing their structure a priori. The method builds upon Spuler et al. 2024 & 2025, with changes that allow for larger, higher-resolution input domains. It identifies distinct atmospheric states associated with different precipitation intensities at target locations, linking discovered patterns directly to their impacts. Importantly, once regimes are identified, indices analogous to traditional teleconnection indices can be derived, enabling comparison with established frameworks while capturing dynamics they may miss.
We apply this method to daily ERA5 fields, targeting precipitation in selected European regions with contrasting dynamical drivers, including Bergen, the Iberian Peninsula, and Copenhagen. This allows us to present teleconnection patterns identified through this approach over the entire Northern Hemisphere as well as relevant sub-regions, including the North Atlantic and Arctic, focusing on extreme precipitation drivers. We find multiple regimes that resemble different flavors of the well-known NAO pattern, alongside circulation states consistent with blocking-like structures. Comparisons with traditional EOF analysis highlight the effects of relaxing linearity and orthogonality constraints. Correlation maps are produced for both methods, enabling direct evaluation of how the data-driven regimes compare to established EOF-based patterns.
The non-linear, data-driven framework remains physically interpretable and avoids the limitations of linear orthogonal decomposition. Though currently applied to ERA5, the approach transfers directly to CMIP6 historical and scenario runs, enabling assessment of how regime frequencies and precipitation associations may shift under climate change. Overall, this study illustrates how ML-based approaches can complement traditional synoptic climatology by allowing circulation–impact relationships to emerge directly from the data.
- Spuler, Fiona R. et al. (2024): Identifying probabilistic weather regimes targeted to a local-scale impact variable. Environmental Data Science, 3, e25.
- Spuler, Fiona R. et al. (2025): Learning predictable and informative dynamical drivers of extreme precipitation using variational autoencoders. Weather and Climate Dynamics, 6, 995-1014.
How to cite: Melcher, J. O., Christensen, J. H., Zhang, C., Langen, P. L., and Yang, S.: Data-Driven Discovery of Non-Linear Weather Regimes driving Regional Precipitation Extremes in Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7026, https://doi.org/10.5194/egusphere-egu26-7026, 2026.
The Mediterranean region is particularly sensitive to extreme precipitation, with Heavy Precipitation Events (HPEs) predominantly occurring in autumn. These events are typically associated with organised, often quasi-stationary mesoscale convective systems that can produce over 100 mm of rainfall in 24 hours, or even in a few hours. This can lead to major damage to infrastructure and loss of life.
Global climate models (GCMs) show uncertainty regarding the future evolution of Mediterranean HPEs. This uncertainty is primarily driven by inter-model differences in projected large-scale atmospheric circulation, which control the occurrence of weather regimes associated with extreme precipitation. Beyond changes in weather regime occurrence, for a given weather regime, uncertainties exist regarding the role of remote climate drivers, such as sea surface temperature or specific humidity anomalies, in influencing the intensity of Mediterranean HPEs and their future evolution.
In this study, we assess how projected changes in Mediterranean HPEs during autumn can be explained by future changes in the occurrence of weather regimes identified as favourable to HPEs. Using ERA5 reanalysis, we identify four weather regimes that favour the occurrence of Mediterranean HPEs. Analyses based on a CMIP6 multi-model ensemble indicate that three of these four HPE-favourable weather regimes are projected to become less frequent towards the end of the century.
Beyond changes in weather regime frequency, we investigate the role of local and remote climate drivers in explaining the spread in GCM projections of future changes in Mediterranean HPEs within a given weather regime. To provide a physical basis for interpreting this dispersion, we first identify the factors that control the intensity of HPEs in the two weather regimes most favourable to HPEs. Based on ERA5, in the most HPE-favourable weather regime, HPEs intensity is controlled by local Mediterranean moisture availability and upper-level circulation over western Europe. Additional remote influences are associated with Atlantic moisture anomalies and Caribbean sea surface temperature anomalies preceding the events. In the second weather regime, HPEs intensity is primarily driven by local Mediterranean moisture conditions, with remote influences are mainly associated with enhanced moisture over North Africa prior to HPEs occurrence.
These results reveal weather-regime-dependent differences in the role of local and remote drivers controlling the intensity of Mediterranean HPEs. This framework can be used to interpret future changes and uncertainties in GCMs projections, and provides a basis for future storyline-based analyses of Mediterranean HPEs.
How to cite: Noirot, L., Bador, M., Boé, J., and Caillaud, C.: Future changes in Mediterranean Heavy Precipitation Events : weather regime frequency and intensity drivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7871, https://doi.org/10.5194/egusphere-egu26-7871, 2026.
Unexpected rainfall events during the January-February dry season over Eastern Africa have significant impact upon society, particularly when they lead to, or exacerbate, ongoing flooding (as in Kenya in 2020 and 2022). Populations across Eastern Africa do not expect rainfall to occur during the January-February dry season, and a lack of preparedness can exacerbate impacts when heavy rainfall does occur. Whilst recent dry season rainfall across Eastern Africa has severely impacted livelihoods and communities, the mechanisms controlling such rainfall are poorly understood, since the majority of previous research has focussed upon the climatological wet seasons. Here, we aim to further explore the drivers of these boreal winter dry season rainfall events.
Recent research suggests that boreal winter precipitation and temperature anomalies over tropical central Africa are influenced by large-scale atmospheric variability originating in the Mediterranean region. Building on these findings, this study investigates the role of Mediterranean troughs in driving January–February dry season rainfall over Eastern Africa.
Our results show that dry season rainfall over Eastern Africa is linked to an upper-level ridge-trough pattern over the Mediterranean. The presence of a ridge in the central Mediterranean and trough in the Eastern Mediterranean leads to westerly wind anomalies across Central Africa, and anomalous westerly moisture transport that enhances moisture over Eastern Africa and a region extending north-east from Eastern Africa into the Arabian Peninsula and Asia. This enhanced moisture leads to enhanced rainfall over Eastern Africa, during the climatologically dry January-February season.
These findings will improve future forecasts of dry season rainfall over Eastern Africa, which will enhance preparedness for future rainfall events. Furthermore, climate projections from CMIP5 and CMIP6 models indicate enhanced dry season rainfall over Eastern Africa under future climate change. Improving our understanding of drivers of present-day dry season rainfall will support our understanding of future rainfall changes.
How to cite: Wainwright, C., Ward, N., Talib, J., Finney, D., Clarke, S., Marsham, J., Taylor, C., and Keane, R.: The role of Mediterranean Troughs on Boreal Winter Dry Season Rainfall over Eastern Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11183, https://doi.org/10.5194/egusphere-egu26-11183, 2026.
Due to their strong temperature gradients, fronts are a focal point of intense precipitation and gustiness related to extratropical cyclones. In addition, sustained condensational heating along trailing cold fronts has been shown to raise background baroclinicity, which can trigger secondary cyclogenesis and, consequentially, cyclone clustering.
To study the driving mechanism, synoptic-scale characteristics, and impacts of fronts throughout their lifecycles, we have developed a front tracking algorithm. A frontal lifecycle is therein defined as a 4-dimensional space-time volume of strong gradients in equivalent potential temperature that is coherent in both time and space.
Based on the climatology of frontal lifecycles, we identify distinct frontogenesis regions in the mid-latitudes. Frontogenesis typically occurs in the lee of meridionally oriented mountain ranges, such as the Rocky Mountains or the Andes, or along western boundary currents, such as the Gulf Stream or the Kuroshio. Fronts forming in these regions travel eastward along the storm tracks over a lifetime of one to two weeks. Such lifecycle characteristics distinguish mid-latitude fronts from stationary or short-lived airmass boundaries in lower latitudes, which are typically classified as fronts by conventional algorithms.
We furthermore associate characteristic dynamic drivers of frontogenesis in the identified frontogenesis regions to lifecycle properties such as duration, strength, and the occurrence of one or multiple secondary cyclogenesis. Thus, investigating how fronts link large-scale atmospheric conditions with downstream storm activity in the Storm Track regions.
How to cite: Lutzmann, J., Spensberger, C., Konstali, K., and Spengler, T.: Identifying Climatological Regions and Driving Mechanisms of Frontogenesis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19853, https://doi.org/10.5194/egusphere-egu26-19853, 2026.
Large-scale precipitation extremes in the mid-latitudes arise from the interaction of multiple synoptic and planetary-scale circulation features. While a considerable body of literature exists on individual drivers, comparability and joint attribution across different spatial scales—from planetary to synoptic—remain challenging.
Here, we use an object-based, spatio-temporal framework to identify and characterise key large-scale drivers of precipitation extremes like atmospheric rivers (ARs), frontal systems, blocking, cut-off lows, and anticyclonic and cyclonic Rossby wave breaking (RWB) using multi-decadal ERA5 reanalysis data. Each circulation driver is identified using established object-tracking algorithms applied to the respective diagnostic fields. The detected circulation objects are linked to spatiotemporal extreme precipitation objects. This allows assessing the relative and joint contributions of different synoptic- and planetary-scale drivers to extreme precipitation intensity, duration, and spatial extent across seasons and hemispheres.
By analysing synoptic- and planetary-scale features within a consistent framework, the work aims to provide insights into the multi-scale dynamical controls on precipitation extremes, supporting dynamical attribution and improving understanding of how trends in dynamics may reflect on trends in precipitation extremes.
How to cite: Thomas, A. and Messori, G.: Contributions of synoptic and planetary-scale drivers to precipitation extremes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5040, https://doi.org/10.5194/egusphere-egu26-5040, 2026.
An increase in precipitation extremes is one of the most robust signals of anthropogenic climate change. However, the latest IPCC assessment still reports low confidence in projected changes over the Mediterranean region. Despite this uncertainty, several Mediterranean cyclones—intense mid-latitude storms—have caused severe precipitation extremes and substantial economic damage in recent decades. The role of climate change in these events remains poorly quantified.
Here, we develop a probabilistic event-storyline approach and apply it to assess projected changes in a high-impact Mediterranean storm track. The storyline describes an autumn large-scale trough over the Iberian Peninsula, followed by cyclone development and northeastward propagation over the western Mediterranean Sea, leading to widespread daily extreme precipitation over the Italian Peninsula. This evolution was characteristic of two notable historical high-impact events: storm Adrian (Vaia) in October 2018 and the November 1966 storm that caused major flooding in Florence. The probability of such events is decomposed into three conditional components: (i) the occurrence of the large-scale trough, (ii) the probability of northeastward-propagating Mediterranean cyclones given the precursor, and (iii) the probability of extreme precipitation given cyclone development. These probabilities are estimated using ERA5 reanalysis and a 17-member ensemble of the CMIP6 EC-Earth3 climate model under present-day and future (SSP2-4.5) climate conditions.
We show that EC-Earth3 provides a satisfactory representation of the Mediterranean autumn storm track, with ERA5-based conditional probabilities lying within the model ensemble spread. However, none of the ensemble members simulates a storm with a trajectory and intensity comparable to storm Adrian, highlighting the rarity of such events. Under SSP2-4.5, the ensemble projects no overall change in the frequency of events following this storyline. This result arises from a compensation between a strong reduction in the frequency of the large-scale precursor (risk ratio r ≈ 0.6), a moderate decrease in cyclone development given the precursor (r ≈ 0.8), and a strong increase in the probability of extreme precipitation conditional on storm development (r ≈ 2). The shallowing of large-scale troughs and the reduced frequency of deep cyclones counteract the expected thermodynamic intensification of precipitation over the Alpine region.
Overall, these findings highlight the need to explicitly account for dynamical changes when assessing future projections of cyclone-driven Mediterranean precipitation extremes. While based on a single large ensemble, the proposed framework can be extended by estimating individual conditional probabilities from different global and regional climate models, offering a pathway to integrate complementary sources of information.
How to cite: Zappa, G., Ghinassi, P., Pascale, S., Grazzini, F., Iacomino, C., Portal, A., and Simolo, C.: A probabilistic event-storyline approach to assessing projected changes in a high-impact Mediterranean storm track, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20954, https://doi.org/10.5194/egusphere-egu26-20954, 2026.
Atmospheric responses to extratropical sea-surface temperature (SST) anomalies are known to be sensitive to model resolution, yet the exact mechanisms controlling this sensitivity remain an open question. In the North Atlantic (NA), where strong air-sea coupling and stormtrack dynamics interact, resolving mesoscale frontal processes may be essential for correctly representing SST-driven atmospheric variability and its feedback onto large-scale circulation patterns such as the North Atlantic Oscillation (NAO).
We analyze a new ensemble of variable-resolution CAM6 simulations with prescribed SST anomalies. The atmospheric grid is globally 110 km and refined over the North Atlantic to 28 km and 14 km, allowing explicit representation of weather fronts and associated mesoscale circulations at the highest resolution. Imposed SST anomalies are derived by regressing the observed NAO index onto SSTs over 1958–2018, producing a cold–warm–cold tripole for a controlled comparison of NA SST feedbacks onto the NAO across resolutions.
We find that the NA SST tripole anomaly induces a positive feedback onto the NAO in the 14-km simulations, whereas this feedback is absent in the 28-km and 110-km configurations, which exhibit weaker and structurally different circulation responses. The atmospheric adjustment pathways also differ markedly across resolutions, with strongly contrasting responses in both the vertical and meridional eddy heat fluxes. In comparison to the lowest resolution, the intermediate resolution exhibits enhanced horizontal eddy heat flux responses, whereas the highest-resolution simulations respond to the positive Gulf Stream SST anomaly primarily through vertical eddy heat fluxes. While the mean states of the two higher-resolution simulations are in closer agreement, the SST-forced responses are more similar between the two lower-resolution simulations, suggesting that resolving the mesoscale might be particularly crucial for correctly representing ocean–atmosphere coupling.
As climate models move toward increasingly high resolution and computationally demanding coupled configurations, these results offer important guidance on the atmospheric resolution required to realistically represent ocean-atmosphere coupling and the climate response to SST perturbations, including those arising from changes in ocean circulation.
How to cite: Müller, J. and Jnglin Wills, R. C.: How Eddy Heat Fluxes Shape the Resolution-Dependent Atmospheric Response to North Atlantic SST Anomalies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14620, https://doi.org/10.5194/egusphere-egu26-14620, 2026.
The North Atlantic (NATL) jet stream plays a central role in shaping weather and climate over the North Atlantic and Europe. It continuously fluctuates in latitude and strength, guiding storm tracks across the basin. When these fluctuations become unusually persistent, they can anchor weather regimes for extended periods, increasing the likelihood of extreme events such as droughts and floods. Here, we investigate the persistence of summer NATL jet latitudinal variability and of the closely related Summer North Atlantic Oscillation using CMIP6 models and the ERA5 reanalysis. Using the relative vorticity tendency equation, we quantify the strength of the eddy–mean flow feedback and show that it explains a large fraction of the intermodel spread in jet persistence. In contrast, differences in feedback strength do not account for the persistence discrepancy between models and ERA5, which we suggest arises from differences in sea–air coupling strength. We further find that intermodel differences in jet persistence are closely linked to differences in the persistence of European precipitation. These results underscore the importance of accurately characterizing dynamical uncertainty, as it directly translates into uncertainty in regional climate impacts.
How to cite: Ossó, A.: The persistence of the Summer North Atlantic Jet Variability: Dynamical Feedbacks and Model‐Observation Discrepancies, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7947, https://doi.org/10.5194/egusphere-egu26-7947, 2026.
Spatially heterogeneous surface warming across continents is strongly governed by atmospheric circulation changes, as demonstrated by observations and climate models. The accelerated warming observed in eastern Europe, northwestern China, eastern Siberia, and western North America aligns with the long-term changes in upper-level zonal winds. However, the hemispheric-scale structure of the upper-tropospheric zonal wind field linked to regional heat extremes remains poorly understood. Using a complex network approach, we identify a north–south-oriented tripole wind anomaly pattern characterised by westerly–easterly–westerly zonal wind anomalies surrounding heat extremes. Variability in this tripole pattern explains up to 70% of the dynamics-induced interannual temperature variability and at least 50% of its long-term warming trend in hotspot regions. Multiple climate models project that the dynamics-induced temperature trend over western North America will double by the end of the 21st century in response to an amplified tripole wind anomaly pattern. Our findings highlight the need to integrate upper-level wind-field dynamics for predicting regional surface temperature.
How to cite: Liu, C., Cai, F., Galfi, V. M., Happé, T., and Coumou, D.: Northern Hemisphere warming hotspots linked to intensified tripole wind anomaly patterns, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12363, https://doi.org/10.5194/egusphere-egu26-12363, 2026.
Daily temperature variations over Europe are strongly linked to fluctuations in the large‐scale atmospheric circulation over the North Atlantic basin. Recently, Europe has been warming rapidly, and it is important to accurately estimate the contribution of atmospheric circulation to this trend.
Here, we present an innovative dynamical adjustment framework based on a convolutional neural network (UNET) trained on CMIP6 simulations and fine-tuned on reanalysis, to estimate the observed circulation-induced temperature at the daily timescale and the subsequent trends over 1979-2024. This approach offers robust estimators at the daily scale, and performs generally better than the commonly used methods for dynamical adjustment (e.g. analogues).
When applying this method on temperature averaged over western Europe, and using the winds at 850 hPa as the circulation predictor, we find that the temperature trends induced by the dynamics between 1979 and 2024 are of 0.05 [-0.03,0.14]°C/decade annually and greater in summer (0.08 [-0.00,0.17]°C/decade) and in winter, but with higher uncertainty (0.09 [-0.11,0.29]°C/decade).
Further, we conduct sensitivity tests to the circulation predictor. Considering the wind at 700 hPa rather than 850 hPa makes no substantial difference, but considering the SLP can increase the estimated dynamical trends up to a factor of 2. This discrepancy might be due to surface processes affecting the temperature-SLP relationship, and our findings suggest that dynamical adjustment methods can be sensitive to the predictor used.
How to cite: Cariou, E., Cattiaux, J., Qasmi, S., and Ribes, A.: Role of the atmospheric circulation in the observed warming over Europe using a neural network., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5268, https://doi.org/10.5194/egusphere-egu26-5268, 2026.
Global warming is expected to have a stronger impact on the Arctic than on the rest of the globe, not only due to interactions between sea ice, snow, and radiation, but also because of the presence of permafrost. These soils store large amounts of carbon (around 1100–1700 Gt), which, if thawed, can affect the carbon cycle, soil hydrology, and surface energy exchanges. Accurately representing soil hydro-thermodynamic processes is therefore essential for realistically simulating Arctic climate change. However, limitations in the representation of soil processes and resolution in land surface models (LSMs) within Earth System Models (ESMs) lead to large uncertainties, for instance leaving it unclear whether the Arctic will become wetter or drier under future warming.
In this study, we use a modified version of the Max Planck Institute for Meteorology ESM (MPI-ESM) in which key thermodynamic and hydrological processes are enhanced particularly in permafrost regions. By tuning model parameters, we generate two idealized set-ups that create wetter and drier soil conditions in permafrost regions and that allow for testing the sensitivity to soil thermo- and hydrodynamics. Based on these configurations, we produce an ensemble of simulations, referred to as the Permafrost Physics Ensemble (PePE), covering the historical (1850-2014) period and extended up to 2300 CE under multiple climate change scenarios.
Our results show that differences in Arctic soil hydrology affect surface energy partitioning and consequently, permafrost extension, near-surface temperature, snow cover and sea ice fraction. Changes in soil moisture modify the background climate state and the strength of feedbacks related to snow and sea ice, contributing to Arctic amplification (AA). In our simulations, AA converges to a warming factor of about 2–3 when external forcing dominates over internal variability. Furthermore, these changes influence the large scale latitudinal gradient and Northern Hemisphere circulation variability by modulating patterns like the Arctic Oscillation (AO).
How to cite: Meabe-Yanguas, N., González-Rouco, J. F., García-Pereira, F., Martínez-Vila, Á., de Vrese, P., Jungclaus, J., and Lorenz, S.: IArctic land surface hydrology influences on regional and hemispheric temperature and circulation responses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13081, https://doi.org/10.5194/egusphere-egu26-13081, 2026.
Large-scale atmospheric circulation and synoptic systems strongly modulate regional environmental variability. Over the western Mediterranean, Saharan dust outbreaks provide a clear circulation-controlled signal, with consequences for aerosol loading, visibility, and air quality. Here we quantify how dust-favourable circulation regimes evolve from recent decades to the end of the 21st century under multiple Shared Socioeconomic Pathways (SSP1-2.6 to SSP5-8.5), using a fixed-centroid synoptic classification applied consistently to reanalyses and daily CMIP6 circulation fields.
Daily atmospheric circulation states were characterized by 850 hPa geopotential height ERA5 reanalysis data fields over North Africa and the western Mediterranean for the period 1980-2014. Each day was assigned to one of 11 pre-defined circulation types (weather regimes) using a non-hierarchical K-means cluster analysis procedure (Salvador et al., 2022). Along with daily regime labels, we retained distances to the nearest centroid and performed internal diagnostics (e.g., centroid stability and assignment consistency) to ensure that the fixed-reference classification remained comparable across datasets.
We linked regimes to an observable regional indicator by evaluating dust relevance using two independent datasets: (I) satellite-constrained dust aerosol extinction optical depth from the MERRA-2 reanalysis (DUEXTTAU) and (II) an observational catalogue of Saharan dust days identified over the Iberian Peninsula. For each regime we quantified conditional dust occurrence and typical dust loading, identifying 6 of the 11 regimes as consistently dust-favourable, i.e., systematically enhancing Saharan dust export and advection into Iberia and the western Mediterranean.
The same classification was applied to 15 CMIP6 models for historical (1980–2014) and future (2020–2100) simulations. We validated each model against ERA5 using metrics that capture agreement in overall regime frequencies, seasonal cycle, interannual variability, and trends, providing an objective basis to interpret uncertainty and to optionally filter or weight models prior to projection.
Finally, we built multi-model ensembles for each SSP and diagnose changes in regime frequency, seasonality, and trend significance through the 21st century. Across SSPs we find a robust increase in dust-favourable regimes, with the strongest changes under SSP5-8.5. In an equal-weight SSP5-8.5 ensemble, the fraction of days assigned to dust-favourable regimes increases from 61.5% (2020s) to 74.5% (2090s), while individual models show larger increases (up to ~20 percentage points), implying sensitivity to model weighting. Regimes typically associated with summer dust transport also become more frequent in spring, indicating a seasonal expansion of dust-conducive synoptic conditions.
By translating projected circulation changes into interpretable regime statistics tied to dust occurrence and loading, this framework provides a transparent bridge between large-scale dynamics and future regional dust-related aerosol variability over the western Mediterranean.
How to cite: Scofield-Teruel, D., Salvador, P., Valero-Garcés, B. L., and Pey, J.: Projected evolution of dust-favourable weather regimes over the western Mediterranean across different climate scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10673, https://doi.org/10.5194/egusphere-egu26-10673, 2026.
Euro-Atlantic weather regimes (WRs) provide a description of quasi-stationary large-scale circulation patterns that strongly modulate European weather variability and extremes. Yet, most existing work focuses on the correlation and impacts of the WR on European weather, while the estimation of ground-level meteorological variables, such as temperature and precipitation, from Euro-Atlantic WR remains largely unexplored.
This contribution presents an AI-based framework that maps Euro-Atlantic WR indices to monthly European 2-m temperature and precipitation anomalies, thereby making explicit the circulation–surface link at seasonal time scales. Using ERA5 (1940–2024), seven year-round WRs and four seasonal WRs (DJF/JJA) are derived from Z500 over the Euro-Atlantic sector via EOF analysis and k-means clustering. A residual neural network takes as input monthly WR indices and calendar information, and reconstructs anomaly fields over Europe.
The model achieves high anomaly correlation and low error across large parts of Europe, especially in winter, and substantially outperforms classical linear WR-composite reconstructions. When the model is driven by the WR indices predicted by the bias-corrected SEAS5, it achieves comparable or better performance across most of the evaluated metrics. To address the question “How accurately do we have to predict the monthly mean WR indices to obtain a seasonal forecast of two-meter temperature and total precipitation that is better than SEAS5?”, we systematically degrade the WR indices, quantify how reconstruction skill depends on WR forecast accuracy, and identify the threshold beyond which the AI reconstruction surpasses the ECMWF SEAS5 seasonal forecast in reproducing European temperature and precipitation anomalies for the winter and summer seasons.
Results demonstrate that a large fraction of the spatial structure of European monthly anomalies can be inferred from the low-frequency Euro-Atlantic regime state. This provides a quantitative basis for AI approaches that exploit regime predictability to enhance sub-seasonal to seasonal forecast of European weather anomalies and related risks.
How to cite: Camilletti, A., Franch, G., Tomasi, E., and Cristoforetti, M.: AI reconstruction of European temperature and precipitation anomalies from Euro-Atlantic weather regimes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18725, https://doi.org/10.5194/egusphere-egu26-18725, 2026.
Historical extreme precipitation events over Central European river catchments often resulted in flooding events. Climate simulations show an increasing intensity of very extreme precipitation in a warmer climate for most parts of Europe. In order to analyse the atmospheric mechanisms leading to the intensification of very extreme precipitation events, we investigate 100-year daily precipitation events over Central European river catchments from large ensembles of multiple CMIP6 global climate models. Extreme events are identified in a historical (1970-2000) and a future (2070-2100, ssp370) period and uncertainties of projected changes are quantified through inter-model differences. Also, future changes are separated into dynamic and thermodynamic contributions with the precipitation scaling diagnostic by O’Gorman & Schneider (2009) and compared to synoptic composites in order to identify the main sources of uncertainty of projected changes and to understand the underlying mechanisms. Extreme precipitation events in the historical period mainly occur during the core summer season (June-August), while there is a slight broadening of the seasonality in the future period towards May and October. Averaged over all models, precipitation intensity in each catchment significantly increases by about 6-9%/K, similar to the Clausius-Clapeyron rate, but the increases vary regionally across models and catchments. This multi-model uncertainty is partly due to a varying representation of dynamical processes between most models, as indicated by the scaling diagnostic, while they mostly agree on a rather homogeneous precipitation increase due to thermodynamic mechanisms. Composites show that projected future changes in the synoptic situation during the extreme events are generally small. Nevertheless, significant changes both in dynamical parameters, such as an intensifying ridge over the North Atlantic, and thermodynamic variables, e.g. larger total column water vapour, enhance the precipitation rate in future events.
How to cite: Ruff, F. and Pfahl, S.: Uncertainty of future changes of very extreme precipitation events over central European river catchments from ensemble simulations of multiple global climate models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9154, https://doi.org/10.5194/egusphere-egu26-9154, 2026.
An ensemble of 12 CMIP6 models was used to project future changes in summer extreme precipitation over eastern China during 2036-2055 under the SSP2-4.5 scenario. Extreme precipitation was quantified using the total precipitation from days exceeding the 95th percentile of wet-day precipitation (R95pTOT). Large inter-model uncertainty is evident over the Huabei region, substantially reducing the reliability of the multi-model ensemble (MME) projection there. To address this inter-model uncertainty, a pattern-based clustering analysis was applied to the MME projections, yielding three distinct and equally likely patterns (Clusters 1-3) of summer extreme precipitation change. Clusters 1 and 3 project increases in extreme precipitation over Huabei for 24.8 mm and 12.7 mm, whereas Cluster 2 indicates a decrease for -1.2 mm. An atmospheric moisture budget analysis reveals that the inter-cluster differences in extreme precipitation changes are primarily driven by dynamic effect associated with contrasting circulations. In Cluster 1, a strengthened and westward-shifted western North Pacific subtropical high (WNPSH) enhances southerly moisture transport, which is associated with cold SSTA over the central tropical Pacific. Cluster 3 exhibits a circulation pattern similar to that of Cluster 1, but with weaker intensity. In contrast, Cluster 2 is characterized by a weakened and eastward-shifted WNPSH at lower level, together with a southward-displaced East Asian subtropical westerly jet at upper level, resulting in less southerly moisture transport. In addition to differences in summer-mean circulation, atmospheric stability conditions over Huabei were compared across these clusters. Clusters 1 and 3 exhibit higher frequency of cases with large convective potential energy (CAPE), whereas Cluster 2 indicates more frequent occurrence of cases with large convective inhibition (CIN).
How to cite: Guo, Y.: Causes of inter-model uncertainty in projecting future summer extreme precipitation changes over eastern China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15469, https://doi.org/10.5194/egusphere-egu26-15469, 2026.
All Mediterranean-type climate regions have experienced recent wintertime precipitation declines, contributing to severe droughts in many cases. Understanding whether these declines are driven primarily by changes in large-scale circulation, atmospheric moisture, or submonthly weather systems is critical for interpreting past trends and anticipating future hydroclimate risk. We use constructed circulation analogues together with a Reynolds-decomposition moisture budget to diagnose the respective roles of dynamic circulation change, thermodynamic humidity change, and submonthly eddy activity in driving these wintertime precipitation trends.
We apply both approaches to observations and reanalyses, multiple large climate model ensembles, and a preindustrial control simulation to understand how these processes regulate moisture convergence and precipitation variability across Mediterranean-type climate regions. Circulation analogue results indicate that observed wintertime precipitation declines are predominantly dynamically driven. However, the thermodynamic drying inferred from the analogue method is stronger than that simulated by large ensembles in all Mediterranean-type regions. Moisture budget diagnostics additionally highlight a substantial contribution from submonthly eddy trends in some locations.
By directly comparing the two frameworks, we highlight that estimates of dynamic and thermodynamic trends can depend strongly on the diagnostic method used. In particular, dynamically driven moisture anomalies and changes in submonthly variability can contaminate thermodynamic estimates derived from both approaches. Using the large ensembles, we show that thermodynamic trends inferred from the two methods can even differ in sign. These results underscore the importance of combining multiple diagnostic methods to more robustly quantify the influence of large-scale circulation and humidity changes on regional precipitation decline.
How to cite: Doane-Solomon, R., Woollings, T., and Simpson, I.: Dynamic and Thermodynamic Drivers of Precipitation Change in Mediterranean-type Climates, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3912, https://doi.org/10.5194/egusphere-egu26-3912, 2026.
Germany has experienced an increasing number of hydroclimatic extreme (HCE) events in recent decades. Heavy rainfall, dry spells, heatwaves, and (flash) droughts have intensified in both frequency and severity under ongoing climate change. However, the definition and monitoring of HCEs remain largely based on near-surface variables (e.g. precipitation, potential evapotranspiration, 2 m air temperature, and soil moisture), while their links to large-scale atmospheric dynamics and synoptic systems are still not well understood.
In this study, we map the occurrence and trends of multiple HCE types prevalent in Germany, investigate their co-occurrence, and assess their teleconnections with atmospheric blocking patterns. We use downscaled, gridded (1 × 1 km), daily data from the German Weather Service for the period 1970–2025 for precipitation, temperature, air humidity, and solar radiation to characterise the occurrence and trends of heavy rainfall, dry spells, heatwaves, and flash droughts. In addition, we use ERA5 reanalysis data to compute the Standardised Precipitation–Evapotranspiration Index (SPEI) and to assess drought occurrence and trends across Germany. ERA5 fields are also employed to identify blocking events following Detring et al. (2021).
Preliminary results indicate positive trends in the occurrence of dry spells, heatwaves, and flash droughts, particularly in southern Germany, and reveal strong links between droughts and Omega blocking, exemplified by the 2022 drought event.
How to cite: Alencar, P. and Rudolph, A.: Bridging Regional Hydroclimatic Extremes and Atmospheric Blocking: A German Case Study, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4856, https://doi.org/10.5194/egusphere-egu26-4856, 2026.
Changes in regional extreme weather and climate events intensify under human-induced global warming. We unravel the drivers and mechanisms driving historical European hot and wet extremes through high-resolution regional climate model simulations, using the ICOsahedral Nonhydrostatic model in climate limited area mode (ICON-CLM). Specifically, we disentangle the contributions of the large-scale weather situation (dynamic conditions) and the local temperature and humidity (thermodynamic conditions) in heatwaves and heavy precipitation events over Europe since 1980.
To this end, we drive ICON-CLM simulations over Europe using boundary conditions from a global model constrained to follow the observed large-scale circulation. We run two sets of experiments: one where both the regional and global model use historical forcing, and one where both use pre-industrial greenhouse gas and aerosol concentrations, while the large-scale circulation remains identical. The difference between these simulations isolates the thermodynamic contribution of anthropogenic climate change to extreme events. Moreover, we perform a simulation with climatological soil moisture, to further quantify the role of land-atmosphere interactions for climate extremes. This model chain and experimental design allows us to disentangle the dynamic and thermodynamic drivers of hot and wet extremes at high resolution, resolving mesoscale processes that are especially critical to heavy precipitation events. It also enables a process-based attribution of all major European extreme events since 1980, moving beyond the case-study paradigm that dominates current research.
How to cite: Bauer, V. M., Schumacher, D. L., and Seneviratne, S. I.: Circulation versus background warming: drivers of European hot and wet extremes since 1980, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20140, https://doi.org/10.5194/egusphere-egu26-20140, 2026.
Floods are among the most disastrous and costly extreme weather events in Europe. Atmospheric blocking patterns (persistent and self-preserved weather systems that propagate very slowly and slow down the large-scale circulation) are part of the main weather regimes in the Euro-Atlantic region and play a central role in shaping the extreme weather of Europe and its impacts on the surface. Nevertheless its socioeconomic importance, the covariability between atmospheric blocking and river flood has rarely been examined on the climate and continental scales. Our study explores the hydrological way that atmospheric blocking propagates into floods and how this relationship varies over space and time, in >6000 basins of Europe during the last 60 years. We analyse flood discharge observations from a pancontinental database and atmospheric and terrestrial variables derived from reanalysis. Our results show clear relationships between flood characteristics and atmospheric blocking occurring in upstream to downstream relative positions. Our analyses highlight that atmospheric blocking significantly influences spatial and temporal variability of flood discharge in Europe, being this relationship modulated by regional hydrological characteristics and the interaction between soil and rainfall. These findings provide a framework to understand the regional impacts of atmospheric blocking over floods and point towards near-climate sources of predictability for floods in Europe.
How to cite: Hernandez, D., Bertola, M., Lun, D., Ahrens, B., McPhee, J., and Blöschl, G.: Flood discharge in Europe influenced by atmospheric blocking, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15011, https://doi.org/10.5194/egusphere-egu26-15011, 2026.
Autumn precipitation in Southeast China (SC) exhibits substantial interannual variability, yet it has received considerably less attention compared to boreal summer precipitation. This study identifies a significant interdecadal shift in the teleconnection between the El Niño-Southern Oscillation (ENSO) and the SC autumn climate. We find that the influence of preceding winter ENSO on the subsequent early autumn precipitation in SC was weak and statistically insignificant during the late 20th century, but has become robustly positive since the early 2000s. Our analysis reveals that in the post-2000s period, El Niño events tend to decay more rapidly and transition into a developing La Niña phase by the following summer. This accelerated decay, coupled with persistent cold sea surface temperature anomalies (SSTA) in the eastern Pacific, sustains the Western North Pacific Anticyclone (WNPAC) from summer into autumn. Moreover, due to the “seesaw pattern” in the developing La Niña phase, the warming central Indo-Pacific triggers a meridional contraction of the local Hadley circulation and contributes to the cyclonic circulation over SC. This circulation change induces anomalous subsidence over the South China Sea and significant ascending motion over inland SC. Consequently, a distinct anticyclone-cyclone dipole emerges after the early 2000s, which provides both the anomalous moisture transport and the dynamical lifting necessary for enhanced precipitation. These findings offer critical insights for improving seasonal forecasting and climate model evaluation for East Asian autumn hydroclimate.
How to cite: Xu, L., Su, H., and Lau, W. K. M.: Strengthened Influence of Preceding Winter ENSO on the Following Early Autumn Precipitation in Southeast China since the Early 2000s, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21038, https://doi.org/10.5194/egusphere-egu26-21038, 2026.
Rainfall events in South America have increased in frequency and intensity over recent decades, causing significant socio-economic impacts. Understanding the large-scale atmospheric circulation patterns (CPs) associated with these events is crucial for improving weather forecasting and risk assessment. Therefore, this study aims to evaluate the skill of the Global Forecast System (GFS) forecasts in reproducing the main CPs and their associated rainfall over western tropical South America.
Daily winds at 200 and 850 hPa from the ERA5 reanalysis and GFS (D0 to D5, where D0 is the initial state and D1–D5 are the 1–5 day forecast) are used. In addition, gridded precipitation data from CHIRPS and GFS are analyzed. All datasets have a spatial resolution of 0.25° and cover the period 2015–2024. A combined principal component analysis (PCA) and k-means clustering approach is applied to identify nine circulation patterns for ERA5 and GFS. Composite analysis is used to relate each CP to its characteristic spatial precipitation patterns. The analysis is structured in two stages: (i) a comparison between ERA5 and the first step of GFS (GFS-D0) and (ii) an evaluation of forecast consistency from GFS-D0 to the subsequent five forecast days (GFS-D1 to GFS-D5). For both stages, the Heidke Skill Score (HSS) is calculated based on the daily occurrence frequency of the CPs.
ERA5 and GFS (D0 to D5) consistently identify the nine CPs, which are classified into three wet, two transitional, and four dry patterns, exhibiting a well-defined seasonal behavior over tropical South America (10°N–30°S, 90°W–30°W). ERA5 and GFS-D0 identify CPs with similar frequency and spatial behavior with a statistically significant association and high seasonal HSS values close to 0.9. When analyzed at the individual CP scale, all patterns exhibit high agreement, although transitional patterns show slightly lower skill. As forecast lead time increases, forecast consistency gradually degrades. HSS values decrease from approximately 0.9 on day 1 to about 0.5 on day 5 during austral winter, autumn, and spring, indicating a predictability limit beyond the third forecast day. Predictability is seasonal, with the highest persistence during austral summer and the lowest during winter. In this context, wet CPs exhibit the greatest stability, while dry patterns show the fastest degradation. Increasing lead time is also associated with growing spatial differences in wind and precipitation fields. Regarding precipitation, CHIRPS and GFS show a consistent spatial behavior, especially for the first forecast day, while these differences become more pronounced by the fifth forecast day. It is important to remark that CHIRPS and GFS present some discrepancies that could be associated with model biases.
These results demonstrate that GFS accurately reproduces dominant circulation patterns at short lead times. However, there is a clear degradation of predictability beyond three days, with important implications for rainfall forecasting and its spatial representation.
How to cite: Quispe, K., Moron, V., Goubanova, K., Martínez, J. A., Zin, I., Junquas, C., Sicart, J. E., Condom, T., Ita, T., Suarez, W., and Espinoza, J.-C.: Assessment of GFS weather forecast model performance in reproducing the main atmospheric circulation patterns linked to precipitation in western tropical South America, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15484, https://doi.org/10.5194/egusphere-egu26-15484, 2026.
Despite ongoing global warming, extreme cold winter events continue to occur, with some winters experiencing more frequent extremes on an interannual scale, impacting densely populated mid-latitude regions. Previous studies have established a close link between Arctic sea ice anomalies and mid-latitude extreme cold events. Our findings reveal that since 2000, two key mechanisms have amplified the interannual variability of Arctic sea ice and its subsequent influence on extreme cold events in Asia. Firstly, accelerated phase transitions of ENSO have intensified the Western North Pacific anticyclone, which excites stronger Rossby waves propagating toward the Arctic. These waves enhance the interannual variability of Arctic sea ice by inducing anomalous anticyclonic circulation over the Arctic, which in turn increases moisture and heat fluxes into the region. Secondly, heightened interannual variability of the North Atlantic Oscillation (NAO) has increased poleward heat and moisture transport into the Arctic, further amplifying sea ice variability on interannual scales. This enhanced Arctic sea ice interannual variability then induces greater atmospheric instability in the Arctic, generating stronger Rossby waves that propagate into mid-latitude Eurasia. Consequently, anomalous anticyclonic circulation and more frequent blocking highs develop over Eurasia, ultimately intensifying the influence of Arctic sea ice on winter cold extremes in Asia.
How to cite: Wang, C. and Su, H.: Enhanced Impact of Arctic Sea Ice on Asian Cold Extremes: Interannual Variability Driven by ENSO and NAO, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17908, https://doi.org/10.5194/egusphere-egu26-17908, 2026.
Keeping oscillation of low frequency of 30~60 days, Butterworth band-pass filter method was used to process the NCEP/NCAR reanalysis data. Based on the application of the low-frequency synoptic map, low frequency features of the two extreme low temperature events were analyzed in order to reveal the characteristics of the low frequency systems during these two events. The results show that in early 2008, large-scale atmospheric systems including blocking-high and upper-level jet stream all featured a distinct 30-60-day oscillation. The positive (negative) anomaly of geopotential height was closely coincided with the low frequency high (low) pressure of the low frequency systems, and the center of positive zonal wind anomaly was consistent with the high value center of low frequency zonal wind. Meanwhile, the positive phase of the AO favored the strengthening of the Middle East jet and the maintenance of the blocking high, resulting in durative low temperature in south China. The 30-60-day oscillation features of the weather systems including upper-level jet and blocking high were not so obvious during “overlord”-level cold wave in 2016. However, the low pressure of low frequency can describe the generating and developing of the polar vortex. Under north air stream at the front of blocking high ridge guidance, the rapid invasion of strong cold air in the middle of polar vortex caused temperature in China drop fast. The low-frequency synoptic map reflected the phase transition of AO before and after the cold wave. The phase of AO was positive in later December 2015 while negative in early January 2016. Then the polar cold air invaded southern China, which can be conclude as the main cause of the sharp drop in temperature. The low-frequency flow field showed the phase transition of AO lagging behind the synoptic flow field about two days during the two events.
How to cite: Li, X.: Low-frequency features during the two typical extreme cold events in China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1782, https://doi.org/10.5194/egusphere-egu26-1782, 2026.
Winter cold extreme events have been observed to frequently take place over North America mainly over its east side, which show significant interannual and decadal variability and cause huge economic losses in the United States. However, it is unclear what leads to the interannual-decadal variability of winter cold extremes over the eastern North America. In this study, we indicate that the decadal variability of winter cold extremes over the eastern North America, whose period is shortened in the recent decades, is mainly tied to Pacific decadal oscillation (PDO), whereas their interannual variability is mainly regulated by Victoria mode (VM). A positive PDO promotes cold extremes in the lower latitudes of the eastern North America mainly owing to the presence of positive Pacific North American (PNA+) patterns, whereas a positive VM is favorable for intense cold extremes in the higher latitudes of the eastern North America mainly due to the occurrence of negative North Pacific oscillation (NPO-) patterns. Thus, the positive VM and PDO combine to significantly contribute to the interannual-to-decadal variability of winter cold extremes over the eastern North America through changes in the winter NPO- and PNA+ patterns due to the variations of meridional background potential vorticity gradient and basic zonal winds. These new findings can help us understand what are the origins of the interannual-decadal variability of winter cold extremes over the eastern North America.
How to cite: Ge, Y.: Winter cold extremes over the eastern North America: Pacific origins of interannual-to-decadal variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2505, https://doi.org/10.5194/egusphere-egu26-2505, 2026.
This study reveals a significant increase in the intensity of interannual variability (IIV) of snowfall frequency during autumn in the mid–high latitudes of Eurasia after 2000. During 2000–2021, the combination of warm and humid air from the Mediterranean with dry and cold air from the Arctic is conducive to increased snowfall frequency over Central Siberian Plateau. Anomalous positive temperatures due to increased specific humidity inhibit the occurrence of snowfall over central Asia. Further research demonstrates that the increased IIV of sea ice growth in the Barents–Kara Seas during autumn plays a crucial role in strengthening the snowfall frequency IIV. The rapid increase in autumn sea ice growth leads to more pronounced negative anomaly of Arctic temperature through the local thermal positive feedback, which enlarges the temperature gradient between the Arctic and the mid–high latitudes of Eurasia, thereby causing anomalous westerlies over Central Siberian Plateau and central Asia. Additionally, the rapid increase in sea ice growth may stimulate southward-propagating Rossby waves, contributing to anomalous cyclone/anticyclone over Central Siberian Plateau/ central Asia. The anomalous westerlies and cyclone/anticyclone circulation will jointly impact the pathways of water vapor transport and thus modulate the IIV of snowfall frequency over Eurasia. Through numerical experiments with increased sea ice growth of different intensities and AMIP-like experiments, it can be demonstrated that the increased IIV of sea ice growth can affect the location of westerlies and stimulate the southward-propagating Rossby waves, thereby promoting an increase in the IIV of snowfall frequency in the mid–high latitudes of Eurasia.
How to cite: Zhou, S., Sun, B., Wang, H., Li, F., Li, H., Li, H., Zhou, B., and He, S.: Increased Interannual Variability of Snowfall Frequency in Eurasia during Autumn after 2000, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2717, https://doi.org/10.5194/egusphere-egu26-2717, 2026.
Changes in Arctic sea ice concentration (SIC) significantly affect mid- to low-latitude climates, yet research regarding its effect on Eurasian climate change in early spring remains insufficient. Based on reanalysis datasets and model simulations, this study reveals a significant weakening in the relationship between the dipole pattern with opposite SIC anomalies in the northern (76◦–82◦N, 20◦–50◦E) and southern (70◦–76◦N, 47◦–67◦E) regions over the Barents Sea during late autumn and the dipole mode of surface air temperature (SAT) with opposite anomalies in the southern (15◦–45◦N, 35◦–100◦E) and northern (50◦–75◦N, 15◦–180◦E) regions over Eurasia during early spring around the 2000s. This change is attributed to different spatial patterns of SIC interannual anomalies in two subperiods. During Period 1 (1978/1979–1999/2000), the dipole SIC anomalous pattern may persist from November toward the following March, which modulates the SAT in situ by affecting turbulent heat flux and longwave radiation, which further strengthening eastward-propagating wave trains originating from the North Atlantic and inducing the dipole SAT pattern in Eurasia in the following March. In contrast, during Period 2 (2000/2001–2021/2022), consistent interannual SIC anomalies over the Barents Sea in late autumn weakened this relationship due to less pronounced wave trains propagating from the Barents Sea to Eurasia. The findings of this paper reveal that different patterns of Arctic SIC can lead to varying characteristics in the Eurasian climate, suggesting the complex relationship between Arctic and Eurasian climates.
How to cite: Yuan, Y., Li, H., Sun, B., Li, F., and He, S.: Interdecadal variation in the relationship between November Barents Sea Ice and the subsequent March Eurasian surface air temperature, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4905, https://doi.org/10.5194/egusphere-egu26-4905, 2026.
The daily temperature variation (DTV) in March over East Asia (EA) during the period 1979–2020 is examined in this study. Using the JRA-55 dataset, we analyze the respective roles of atmospheric circulation and global warming in modulating regional DTV. Among the high-frequency components of surface air temperature (SAT) variability in spring, March DTV exhibits a statistically significant increasing trend over EA during the four decades. Composite analysis reveals that above-normal March DTV is closely associated with anomalous anticyclonic circulation over the North Pacific and anomalous cyclonic circulation over Russia. These circulation anomalies enhance the meridional SAT gradient and increase the frequency of mid-latitude synoptic-scale pressure systems traversing EA. Consequently, enhanced thermal advection leads to increased variability in March SAT across the region. Furthermore, the circulation anomaly pattern linked to large March DTV displays characteristics consistent with a weakened EA winter monsoon (EAWM). Regression analyses employing indices of the EAWM and the long-term global warming trend indicate that both large-scale atmospheric circulation variability and global warming have contributed significantly to the observed changes in March DTV over EA. In particular, spatially heterogeneous warming rates and localized soil drying during the period are likely key factors explaining the influence of global warming on the increasing March DTV in EA.
How to cite: Ahn, J.-B.: Increasing March Daily Temperature Variation over East Asia: Roles of Atmospheric Circulation and Global Warming, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7876, https://doi.org/10.5194/egusphere-egu26-7876, 2026.
Summer anticyclones are known for their strong connection to extreme near-surface temperatures, potentially leading to severe natural hazards in the mid-latitudes. Although our understanding of the processes causing these heat extremes is growing, the causal relationship between soil conditions, near-surface air temperature and the synoptic systems above them is still far from being fully understood.
The aim of this work is to provide insight into the interaction between near-surface air masses and heat-generating mid-tropospheric summer anticyclones. Using Lagrangian analyses and a temperature change decomposition method, we illustrate the contributions from advection, diabatic and adiabatic heating in air streams during different phases of the anticyclone life cycle from a composite perspective. Moreover we look for coherent trajectory patterns that could contribute to the coupling of near-surface temperature extremes and the mid-tropospheric flow.
We demonstrate that the role of diabatic warming increases in the southeast of the mid-level anticyclone during more intense heat waves over land. In contrast, the areas in the west of the anticyclone, where the heat waves occur, are primarily affected by advection and adiabatic warming. We also provide evidence for the occurrence of coherent air streams injected from the outflow of dry intrusions or post frontal subsidence in troughs adjacent to the anticyclone and explore their implications for the life cycle of the anticyclone.
How to cite: Thomas, M. and Pfahl, S.: Pathways and processes leading to the warming of air masses in northern hemispheric summer anticyclones, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14213, https://doi.org/10.5194/egusphere-egu26-14213, 2026.
Droughts are a recurring feature of climate variability in Croatia and are of great importance as they cause high economic losses and severe damage in particular to the agriculture and water management sectors. Understanding the origin and course of drought events, as well as developing forecasting approaches, requires knowledge of the synoptic framework of droughts. In this context, weather and circulation type classifications provide one feasible approach for characterizing main synoptic patterns and for analyzing related impacts on drought dynamics.
Against this background, a new circulation type classification for Croatia has been developed and applied to time series of the Standardized Precipitation Index (SPI) to analyze the spatial and temporal variability of drought events in Croatia.
In our contribution the development of the new classification is documented and the resulting 20 circulation types are characterized with regard to their main synoptic-climatological properties.
Using SPI time series for 31 stations from the official Croatian network for the period from 1981 to 2020, we investigate the relationship between weather patterns and drought events. Based on the estimation of percentage anomalies significant drought relevant circulation types are identified for varying SPI period lengths and drought thresholds also taking into account seasonal and spatial variations. Temporal variations in occurrence frequencies of drought-relevant circulation types are then related to SPI time series and the relevance of the circulation types for the temporal drought variability is statistically quantified.
Preliminary results of our analyses show that:
- identified relevant weather patterns reflect clear synoptic configurations associated with drought.
- Partly distinct differences in drought-related patterns can be observed between seasons and depending on the SPI-period length, while
- respective differences between climatic regions of Croatia are barely pronounced.
- Large parts of the interannual SPI variability at the stations can be attributed to corresponding frequency variations in drought-relevant circulation types.
How to cite: Beck, C. and Marinović-Šekerija, I.: The influence of circulation types on drought variability in Croatia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14690, https://doi.org/10.5194/egusphere-egu26-14690, 2026.
The thickness of the planetary boundary layer is one of the most important factors determining vertical transport and concentration of pollutants near the surface. However, the boundary layer height (BLH) as well as its structure, especially the occurrence of stable layering, depends to a large extent on the synoptic situation, i.e. mainly on strength and direction of the synoptic wind, advection of air masses of different properties and cloudiness. Several former studies show an increasing trend of the BLH, especially during daytime, throughout the last decades. The study presented here evaluates the dependence of the BLH for a selected region around the city of Augsburg in southern Germany on synopticcirculation types in order to better understand short term as well as long term BLH changes and their effects on the urban air quality of Augsburg.
Boundary layer heights are retrieved from ceilometer measurement series starting in 2017 using a routine for estimating BLH from Vaisala CL51 ceilometer laser backscatter data. They are compared to hourly ERA5 BLH data (1940 to 2025) in order to evaluate the uncertainty when using the ERA5 reanalysis data as replacement for observation data at the considered location for long term studies.
The algorithm for determination of synoptic circulation and weather type patterns related to the BLH is based on the SANDRA algorithm (Simulated Annealing and Diversified Randomization) where the target variable multiplied by an empirically determined weight is included into the clustering process. Different synoptic field variables including geopotential height, wind components and temperature at different atmospheric heights as well as the influence of cloud cover are examined and their contribution to the explained variance of the boundary layer height is presented and discussed. Finally, the suitability of the prescribed correlations for establishing statistical short term prediction models is discussed.
How to cite: Philipp, A., Münkel, C., Straub, A., Beck, C., and Schäfer, K.: Synoptic circulation types related to the boundary layer height in Augsburg, Germany, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22703, https://doi.org/10.5194/egusphere-egu26-22703, 2026.
The North Atlantic Oscillation (NAO) has been confirmed to be closely related to the weather and climate in many regions of the Northern Hemisphere; however, its effect and mechanism upon the formation of dust events (DEs) in China have rarely been discussed. By using the station observation dataset and multi reanalysis datasets, it is found that the spring dust aerosols (DAs) in North China (30-40° N, 105- 120° E), a non-dust source region, show high values with a strong interannual variability, and the spring DAs in North China are significantly correlated with the previous winter's NAO. According to the nine spring DEs affected significantly by the negative phase of the preceding winter's NAO in North China during 1980-2020, it is shown that before the outbreak of DEs, due to the transient eddy momentum (heat) convergence (divergence) over the DA source regions, the zonal wind speed increases in the upper-level troposphere, strengthening the zonal wind in the middle-lower levels through momentum downward transmission. Simultaneously, there is transient eddy momentum (heat) divergence (convergence) around the Ural Mountains, which is favorable for the establishment and maintenance of the Ural ridge, as well as the development of the air temperature and vorticity advections. The combined effects of temperature and vorticity advections result in the Siberian Highs and Mongolian cyclone to be established, strengthen, and move southward near the surface, guiding the cold air from high latitudes southward, and is favorable for the uplift and transmission of DAs to North China downstream. Simultaneously, the changes in upstream transient eddy flux transport can cause both energy and mass divergence in North China, resulting in diminishing winds during DEs, which would facilitate the maintenance of dust aerosols here and promote the outbreak of DEs. This study reveals the impact of transient eddy flux transport on the dusty weather anomalies modulated by the NAO negative signal in North China, which deepens the understanding of the formation mechanism of DEs in China.
How to cite: Li, Y.: Influence of the previous North Atlantic Oscillation (NAO) on the spring dust aerosols over North China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1779, https://doi.org/10.5194/egusphere-egu26-1779, 2026.
The Northern Hemisphere (NH) midlatitudes have exhibited intensified summer heat extremes over the past decades and growing evidence suggests that this reflects not only the thermodynamic background warming but also dynamical variability that promotes persistent ridging and land-atmosphere feedback. Here we assess the extent to which tropical-extratropical interactions, and in particular ENSO-like tropical Pacific variability, modulate NH summer circulation and eddy-mean flow feedbacks in ways that amplify midlatitude warming and extremes in addition to studying how the dynamical contribution may evolve under anthropogenic forcing. The analysis is motivated by an observed shift in the distribution of the summer daily surface temperatures across the midlatitudes towards more extreme warm conditions during years when tropical Pacific sea surface temperatures (SST) are anomalously cold over the period 1979-2024. The La Niña-like conditions in the tropics are accompanied by a coherent upper-tropospheric response characterized by enhanced ridging and meridional convergence of eddy momentum flux around 40°N. However, trends in eddy momentum flux convergence over the same period show opposite sign changes relative to the La Niña composite, despite tropical Pacific SST trends that appear La Niña-like, emphasizing that ENSO-like SST patterns in trends do not necessarily imply ENSO-like eddy-mean flow feedbacks and highlighting the role of the evolving mean state conditions. To isolate the role of radiative forcing versus SST changes, we analyze two sets of tropical Pacific pacemaker simulations conducted with the fully-coupled Community Earth System Model v.2, in which reanalysis SST anomalies are prescribed while radiative forcing is either held fixed or allowed to evolve. This design allows us to study how the evolving forced mean state alters the tropical precipitation/divergence response to SST and the midlatitude waveguide and eddy momentum convergence. We find that the observed shift towards more extreme warm summers during La Niña years emerges only when radiative forcing is fixed despite identical tropical Pacific SST nudging. We interpret this contrast through CO2-driven “fast” atmospheric adjustments (reduced radiative cooling) that weaken tropical vertical motions independent of SST warming, thereby altering the effective ENSO heating anomalies that drive teleconnections. Implications for the dynamical modulation of NH summer hot extremes by ENSO under continued anthropogenic forcing are discussed. Lastly, we show that a composite conditioned on capturing the observed trends in summer heat extremes in the CESM2 Large Ensemble also shows a La Niña-like tropical Pacific cooling and a chain of high-pressure trends across the NH midlatitudes, which suggests that tropical-extratropical interactions can amplify midlatitude summer warming albeit with a likely mean state-dependent response.
How to cite: Topál, D., Ding, Q., Fichefet, T., and Torma, C.: Summer warming in the Northern Hemisphere midlatitudes amplified by tropical-extratropical interactions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16564, https://doi.org/10.5194/egusphere-egu26-16564, 2026.
Posters virtual: Fri, 8 May, 14:00–18:00 | vPoster spot 4
EGU26-10629 | Posters virtual | VPS7
On the links between large-scale atmospheric circulation and extreme events in the Danube basin, identified by Palmer drought indicesFri, 08 May, 15:06–15:09 (CEST) vPoster spot 4
The aim of this study is to explore links between large-scale atmospheric circulation and meteorological and hydrological drought events in the Danube basin.
Based on previous studies on the relationship between large-scale atmospheric circulation and the occurrence of extreme events in the Danube basin, especially in the middle and lower Danube basin, two climate indices were considered. The first index characterizes the Greenland-Balkan Oscillation (GBOI) and the second is the well-known index associated with the North Atlantic Oscillation (NAOI). For meteorological and hydrological drought, the Palmer Drought Severity Index (PDSI), with applications especially in the agricultural field, and, respectively, the Palmer Hydrological Drought Index (PHDI), especially useful for estimating drought affecting water resources on longer timescales, were taken into account.
To find the type of connection (linear/non-linear) between large-scale climate indices (GBOI, NAOI) and those at the regional scale (PDSI, PHDI), elements from information theory, such as mutual information, were applied. To get time-frequency details, bivariate and multivariate wavelet transforms were used.
The analyses were performed separately for each season. The most statistically significant results were obtained both for the link between GBOI and PDSI, in the winter season, and for that between GBOI and the two analysed Palmer indices, in the spring season.
Regarding the influence of NAOI, it is much less than that of GBOI, but it can be considered relatively significant in winter on PDSI and in spring on PHDI.
From the wavelet coherence analyses it was observed that the significant coherences between the large-scale atmospheric indices and the analysed Palmer drought indices are located in frequency bands, corresponding to ~11–year, 22-year and 33-year period bands, that can be associated with the Schwabe, Hale and even Bruckner solar activity cycles.
In exploring regional-scale droughts, for the future studies, it appeared evident the importance of taking into account of the simultaneous or delayed influence of solar activity on terrestrial climate variables.
How to cite: Mares, C., Mares, I., Dobrica, V., and Demetrescu, C.: On the links between large-scale atmospheric circulation and extreme events in the Danube basin, identified by Palmer drought indices, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10629, https://doi.org/10.5194/egusphere-egu26-10629, 2026.
