Despite substantial progress in numerical modelling in recent decades, predictability for weather and extreme events is often limited and the assessments of future changes remain uncertain. This underscores the need to improve our understanding of the complex, nonlinear interactions of dynamical and physical processes that influence predictability at different lead times and determine the location, timing, and magnitude of extreme events.
This session will discuss our current understanding of how physical and dynamical processes connect atmospheric motions across temporal and spatial scales and how this relates to intrinsic and practical predictability of various weather phenomena. We particularly welcome contributions advancing our understanding, prediction, and future projections of weather and climate extremes, from both an applied and theoretical viewpoint, and with socio-economic impacts, e.g. on power systems.
Topics of interest include but are not limited to:
(1) Synoptic-scale atmospheric dynamics affecting the timing, positioning, and amplitude of weather events (e.g., the stationarity and amplitude of Rossby waves).
(2) Large-scale atmospheric and oceanic influences (e.g., the stratosphere, the Artic, or tropical oceans) on atmospheric variability and predictability in the midlatitudes.
(3) Intrinsic limits of predictability for various atmospheric phenomena and their link to the multi-scale, non-linear nature of atmospheric dynamics.
(4) Practical limits of predictability and the representation of atmospheric phenomena in numerical weather prediction and climate models including sensitivities to the model physics.
(5) Weather and climate extremes, including compound extreme events, their dynamics, predictability, and representation in weather and climate models.
(6) Statistical and mathematical approaches for the study of extreme events.
(7) Impact and risk assessment analyses of extreme events, with a focus on renewable power systems and Europe.
The North Atlantic jet stream is generally projected to shift poleward and extend eastward in winter in response to global warming. However, the spread of climate model projections of the jet stream changes is large, causing substantial uncertainty in projections of future European climate. The uncertainty in changes of surface variables such as precipitation may be better understood by forming storylines of jet stream changes. Storylines are defined here as physically self-consistent unfoldings of future events. They are often formed by regression with possible remote drivers of circulation changes, such as sea surface warming patterns. However, the regression framework leads to a long chain of causality from drivers to effects of circulation changes. Here, we utilize a novel method for forming storylines of European future climate based directly on relevant jet stream changes using k-means clustering. We cluster the 850 hPa zonal wind field changes in 303 simulations from 50 models in the sixth phase of the Coupled Model Intercomparison Project (CMIP6). The aim of this work is to form storylines of different possible types of North Atlantic jet stream changes to understand the spread of European winter climate projections by the end of the century in CMIP6 simulations. We investigate changes in precipitation, surface air temperature, solar radiation, and surface wind speed due to their connections to renewable energy resources.
We find that the most important North Atlantic jet stream changes for European winter climate are related to the eastward extension of the jet over Europe. We form four clustering-based storylines characterized by different levels of intensification and poleward shift of the eastward extension. These storylines capture a major part of the climate projection uncertainty in Europe. The storyline with the strongest extension intensification projects the strongest wettening in northern Europe and strongest surface wind speed increase in western Europe, while the storyline with the strongest poleward shift of the extension projects the weakest wettening and strongest increase in solar radiation in western Europe. Our results highlight the interconnections between future changes in different variables and in different parts of Europe.
How to cite: Koskentausta, J., Karpechko, A., and Sinclair, V.: European winter climate storylines based on changes in the North Atlantic jet stream’s eastward extension, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-267, https://doi.org/10.5194/ems2026-267, 2026.
Atmospheric blocking events are long-lasting quasi-stationary high-pressure systems that persist for several days to weeks. They have been strongly linked to temperature extremes, such as winter cold spells and summer heatwaves, which can have substantial socio-economic impacts across various regions. State-of-the-art global climate models simulations of atmospheric blocking still underrepresent blocking frequency and persistence. Biases in the mean state, together with biases in sea surface temperatures, coarse horizontal resolution, and the choice of blocking detection method, have been highlighted as key contributors to such discrepancies. Recent studies highlight that increasing horizontal resolution can improve atmospheric blocking representation, with improvements being region-, season- and detection method-dependent. In this study, we aim to evaluate atmospheric blocking representation in the most advanced existing Earth System Models across the northern hemisphere. Blocking events are detected using an Eulerian blocking index based on the reversal of the meridional gradient of daily geopotential height at 500 hPa. We analyze a range of post-CMIP6 simulations from the Optimal high resolution Earth System Models (OptimESM) project, and compare blocking activity against the ERA5 dataset for the 1979-2014 period. Preliminary results indicate that, compared to ERA5, the historical simulations generally underestimate Scandinavian blocking frequency throughout the year, with underestimation also occurring in Greenland for all seasons except boreal spring. For Central Atlantic, models tend to overestimate blocking during winter and spring, but underestimate it in summer and autumn. Blocking frequency in the North Pacific is overestimated in winter and spring and underestimated in summer, while showing the closest agreement with ERA5 in autumn. Furthermore, trends in atmospheric blocking frequency for the 1979-2014 period show substantial regional and seasonal variability when comparing ERA5 reanalysis with model simulations, while also emphasizing the ongoing disagreement between reanalysis and model simulations.
How to cite: Loizou, P., Karpasitis, A., and Zittis, G.: Evaluating Northern Hemisphere Atmospheric Blocking in post-CMIP6 Earth System Models, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-328, https://doi.org/10.5194/ems2026-328, 2026.
The dynamical properties of the North Atlantic storm track, and their response to ongoing climate change, remain far less constrained than the thermodynamic aspects of the climate system. The evolution of the North Atlantic storm track over recent decades shows an unclear picture. Previous observational studies have largely examined isolated diagnostics, over shorter periods, or within modelbased frameworks; to the best of our knowledge, a combined assessment of the storm track diagnostics and the associated mean flow over an observational record of this length remains lacking.
This study investigates trends in North Atlantic storm track dynamics, focusing on meridional heat fluxes and baroclinicity, variables that are coupled through the baroclinic life cycle of mid-latitude cyclones and collectively describe the state of the upstream storm track. The analysis uses ERA5 data, which now spans more than 80 years with a homogeneous data assimilation system, enabling multidecadal trend detection.
The analysis reveals a pronounced non-stationarity in North Atlantic storm track baroclinicity over the full examined timescale, with periods of enhanced and suppressed Eady growth rate and heat flux that do not conform to a monotonic forced trend. The degree of co-variability among the two dynamically relevant diagnostics differs substantially between sub-periods, indicating that the storm track’s variance structure does not evolve uniformly on decadal timescales but undergoes phases of dynamical reorganisation. These results are consistent with a substantial role of internal variability in modulating storm track variance on multi-decadal timescales.
Our results suggest that projected trends in the dynamics of the North Atlantic storm track may well be non-uniform and difficult to disentangle from apparent decadal internal variability.
This research was funded by the Polish National Agency for Academic Exchange (NAWA) under the Bekker Programme (grant no. BPN/BEK/2024/1/00180). It was further supported by the Department of Meteorology, University of Reading.
How to cite: Wojciechowska, I. and Ambaum, M. H. P.: Observed multi-decadal trends in North Atlantic storm track dynamics: baroclinic diagnostics from ERA5 (1945–2024), EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-342, https://doi.org/10.5194/ems2026-342, 2026.
Weather regimes are valuable for energy sector applications as some are associated with higher risk of energy shortages, e.g. blocking regimes in winter. However, there are many uncertainties linked to the implementation of weather regimes, with connected risks for the energy sector. Especially relevant is the impact of climate change on the energy sector and the question whether weather regimes are suitable to use for that.
The weather regime uncertainties are investigated by studying three methodologically different Euro-Atlantic weather regime definitions. These definitions consist of 4, 6 or 7 weather regimes and are determined using different pre- and post-processing steps. We systematically compare the three methods and analyse their methodological and spatio-temporal sensitivity using ERA-5 reanalysis data. We find that the occurrence and persistence of the identified weather regimes can be sensitive to small changes in the methodology, with a significant impact of the training period. When considering 4 or 7 weather regimes, this results in unstable regime patterns.
Next, we investigate the representation of weather regimes in CMIP6 models. The regimes that are identified for the studied CMIP6 models are often different to those identified for ERA-5. The definition with 4 weather regimes is best represented in the CMIP6 models, where the definitions using 6 or 7 regimes are unstable with model-dependent regime patterns. This raises the question whether CMIP6 models are suitable to study the effects of climate change when using weather regimes to get to energy sector impacts. As there is substantial instability and uncertainty associated with the different weather regime definitions, a cautious approach is recommended.
How to cite: Hompes, L., Falkena, S., and Stoop, L.: Uncertainty within Euro-Atlantic Weather Regime Definitions, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-453, https://doi.org/10.5194/ems2026-453, 2026.
The recent trend in the Northern Hemisphere summer atmospheric circulation resembles a Rossby wave with wave number 5. These quasi-stationary circumglobal Rossby waves are associated with extreme events, such as heatwaves, droughts, and floods, that can have catastrophic societal impacts. Therefore, understanding the drivers of these Rossby waves and evaluating their representation in climate models is a key scientific challenge. However, identifying the drivers of such patterns can be difficult because traditional approaches such as simple correlation analysis may not capture the complex, nonlinear interactions inherent in atmospheric teleconnections. To address this, explainable artificial intelligence (XAI) offers a promising alternative.
In this study, we test the hypothesis that the observed trend is partially driven by changes in the tropical oceans, which can influence midlatitude weather patterns through tropical-extratropical teleconnections. Using an explainable neural network approach, we aim to identify key tropical regions that drive the midlatitude wave-5 pattern on subseasonal timescales. The methodology is composed of two steps. First, a convolutional neural network is trained to predict the wave-5 pattern using tropical outgoing longwave radiation (OLR) fields as input. Next, we apply explainability techniques such as layer-wise relevance propagation to identify which input features are most important for accurate predictions. This process generates heat maps highlighting tropical regions that are important for the generation of a wave-5 pattern. Subsequently, changes in sea surface temperatures (SSTs) and OLR in the identified regions can be assessed as well as their correlation to the trend in the Northern Hemisphere circulation. We will present some preliminary outputs of this analysis.
How to cite: Stoffels, R., Happé, T., Kofinas, M., Walt, E., Galfi, V. M., and Coumou, D.: Using an explainable neural network to identify tropical drivers of the Northern Hemisphere wave-5 trend pattern , EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-649, https://doi.org/10.5194/ems2026-649, 2026.
The stratospheric polar vortex (SPV) is a dominant feature of the winter stratosphere, characterized by circumpolar westerly winds. In the mid-latitudes, the SPV edge separates the lower stratosphere from the upper troposphere and is primarily deformed by tropospheric Rossby wave breaking (RWB). The geometry of the SPV edge strongly influences jet stream orientation, storm activity, blocking patterns, and surface weather. Moreover, the SPV’s response to climate change remains a major source of inter-model spread in CMIP6 simulations.
The inconsistent responses of the SPV across CMIP6 models are linked to the large internal variability of nonlinear PV dynamics, highlighting the importance of daily, synoptic-scale patterns. Previous classification efforts of the SPV edge have typically been monthly and often rely on zonal-mean diagnostics, limiting their ability to capture synoptic-scale variability.
To address this, we develop a novel framework for daily, year-round classification of the lower SPV edge, focusing on recurring RWB patterns that dominate SPV variability. Our analysis targets the 6–7 PVU band on the 350 K isentropic surface, a region that is (i) strictly stratospheric year-round, avoiding topographic intersections, (ii) closely aligned with the maximum PV gradient approach and the sub-polar jet stream, (iii) materially conserved in the absence of diabatic processes, and (iv) indicative of jet intensity through PV-band width. Using a self-organizing map (SOM) approach, we identify 12 leading regimes of the lower SPV edge.
Applied to ERA5 reanalysis data (1979–2024), the PV-band classification captures meaningful PV configurations and anomalies across the 350 K surface, consistent with well-established weather-scale patterns (e.g., Greenland and Scandinavian blocking) and SPV modes (stronger/weaker SPV and SPV edge). These modes exhibit immediate impacts both downward to the surface and upward into the stratosphere. This framework provides a powerful tool for evaluating inter-model spread in climate simulations and analyzing SPV responses to climate change, by quantifying deviations from observed SPV-edge configurations and their temporal characteristics.
How to cite: Givon, Y., Jnglin Wills, R., and Wesniuk, J.: PV-Based Classification of the Polar Vortex Edge: Variability and Impacts of Rossby Wave Breaking, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-652, https://doi.org/10.5194/ems2026-652, 2026.
Extreme heat poses escalating socio-economic and ecological risks, yet the most severe high-impact heat extremes that would be possible today remain poorly understood. Using thousands of plausible ensemble-boosting current climate storylines, we reveal the risk for far more intense and unprecedented heatwaves, which surpass historical extremes in both intensity and particularly in persistence by large margins, and greatly exceed levels considered extreme in a 3°C warmer world. Worst-case boosted sotrylines depict extreme heatwave intensities four to six times more intense than those observed in 2003 and 2018 over Europe, the most extreme years on record, occurring concurrently with soil moisture deficits or sea surface temperatures more than one standard deviation more intense. These findings reveal the potential for far more intense heat compounding with other system stressors in unprecedented levels.
The most extreme heatwaves are preceded by severe soil moisture depletion, both locally and upstream of the region of extreme heat, as well as by strong ocean temperature gradients, with extremely warm anomalies in the nearby basins and cold anomalies in the subpolar North Atlantic region. Furthermore, our work reveals an additional risk: worst-case heatwaves occur predominantly after another extreme heatwave. This highlights the potential for aggravated impacts due to decreased recovery times and intensified heat stress on humans, ecosystems and infrastructure made more vulnerable by the first event. Given the scale, intensity, and unprecedented successive and compounding nature of these worst-case heat storylines, we underscore the urgent need for well-informed adaptation strategies that sufficiently reflect these risks.
How to cite: Suarez-Gutierrez, L., Beyerle, U., Mittermeier, M., Vautard, R., and Fischer, E. M.: Worst-Case European Heat Storylines generated using Ensemble Boosting, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-35, https://doi.org/10.5194/ems2026-35, 2026.
Heatwaves are among the most impactful climate extremes in Europe. Their recurrence, defined as sequences of heat events separated by short breaks, is projected to increase disproportionately under climate change. Yet the physical drivers of recurrent heatwaves remain poorly understood, partly because recurrence emerges from interacting processes operating across spatial scales, from local land–atmosphere feedbacks to large-scale circulation, and studies often focus on only one scale at a time. We develop a unified framework to investigate heatwave recurrence across local, object, and continental scales over Europe using the European Centre for Medium-Range Weather Forecasts ERA5 reanalysis for 1950–2024.
Our preliminary results reveal complementary insights at each spatial scale. Local recurrence, that is heatwaves at one location separated by less than seven days, exhibit weaker daily temperature and soil moisture anomalies than isolated events. However, heatwave object recurrence, defined as spatially contiguous heatwave objects generating strong local recurrence, shows higher soil moisture depletion and higher temperatures compared to single events. They further persist longer and are associated with distinct atmospheric circulation regimes. Continental recurrence reflects summers in which multiple heatwave objects overlap, affecting large areas or striking the same regions repeatedly. It emerges as a distinct dimension of summer heat extremes rather than simply reflecting anomalously warm conditions. Summers with high continental recurrence feature more heatwaves, larger affected areas, higher temperature anomalies, and earlier, more persistent soil moisture depletion compared to summers with isolated events. Further, high continental recurrence is strongly related to the occurrence of locally recurrent events.
These findings demonstrate that recurrence is a cross-scale phenomenon and highlight the importance of integrating complementary spatial perspectives to better understand compound heat extremes and the coupled atmospheric–land surface processes that govern them.
How to cite: Dillerup, I., Messori, G., Lemburg, A., Buschow, S., and Pinto, J. G.: How atmospheric and surface conditions shape recurrent heatwaves in Europe: From local to continental scale, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-276, https://doi.org/10.5194/ems2026-276, 2026.
It is widely known that the Tibetan Plateau (TP) has great impacts on the regional and global weather/climate by the dynamic and thermodynamic forcing. As the key region, the climate of the TP is receiving more and more attention. Low temperature is one of the typical meteorological disasters, exerting serious effects on the livestock farming over the TP. Therefore, in the present study, the possible mechanisms of the interannual variability of the early spring extreme cold days (ECD) over the TP are probed into, and our analyses suggest that the factors contributing to the TP ECD in March and April are markedly diverse. In March, the local anomalies of the snow cover and cyclone over the TP provide a suitable background for the occurrence of the ECD by changing the surface heat flux and leading to the adiabatic cooling and increase of the cloud cover related to the ascending motion, respectively. Further study indicates that the synergetic effect of the Arctic Oscillation and Western Pacific pattern is conducive to the formation of the aforementioned cyclonic anomaly over the TP. However, in April, the local cold temperature advection along with the significant northerly/northwesterly anomalies over the TP favors the condition for the more ECD on the interannual timescale. The Eurasian pattern and tripolar pattern of the anomalous North Atlantic sea surface temperature are found to show the crucial impacts on the concurrent TP ECD through stimulating the wave trains individually and producing the above local horizontal winds anomalies over the TP.
How to cite: Han, S., Sun, J., Su, B., and Zhang, M.: Interannual Variation of the Early Spring Extreme Cold Days over the Tibetan Plateau and the Possible Mechanisms, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-189, https://doi.org/10.5194/ems2026-189, 2026.
To investigate the spatio-temporal characteristics and its impact of winter extreme low temperature in North Asia, the extreme cold days index (TX10p) is used in this study. The first empirical orthogonal function (EOF) mode of extreme cold days in North Asia exhibits a consistent distribution centered on Lake Baikal, primarily showing interannual variability. It is influenced by two key factors: snow cover in the previous autumn and the Arctic Oscillation (AO) in the wintertime, modulated by the land-atmosphere. Specifically, the previous autumn snow cover can affect the strength of mid-high latitude troughs and ridges by adjusting the meridional temperature gradient and the strength of the westerly wind, thereby influencing cold waves. Meanwhile, the winter AO can modulate the southward movement of polar cold air by adjusting the strength of the polar vortex, ultimately impacting the frequency of extreme cold days in North Asia.
The second EOF mode of the extreme cold days in North Asia displays a northeast-southwest dipole distribution bounded by Lake Baikal, mainly showing an interdecadal transition. Temporrally, before 2000, the pattern featured more cold days in the northeast and less in the southwest, with opposite trend in the later period. Spatially, the spatial distribution also has a corresponding interdecadal change around 2000. The northeast-southwest boundary of the dipole pattern shifted from around 50°N in the early period to approximately 60°N in the later period, reflecting an expansion of southwest region. The interdecadal change characteristics of the second mode are mainly modulated by the combined effects of the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO). Under the synergistic changes of the AMO and PDO phases, the sea surface temperatures of the Pacific and Atlantic can influence the strength of the polar vortex, thereby affecting the north-south gradient in the mid to high latitudes, and the strengths of westerlies and troughs and ridges, ultimately being conducive or not conducive to the southward movement of cold air. In addition, shifts in the PDO phase impact the strength and position of the Aleutian Low, which alters the East Asian trough and contributes to the north-south displacement of the EOF2 mode's spatial pattern.
How to cite: Gao, Y.: Interannual-interdecadal variability of extreme low temperature in North Asia and its driving mechanisms, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-194, https://doi.org/10.5194/ems2026-194, 2026.
Atmospheric deserts originate in the hot, dry and deep convective boundary layers of arid, desert and/or elevated regions and can be transported over thousands of kilometres. They are a concept recently introduced by our group as a generalisation of elevated mixed layers, which retain their well-mixed properties and have been found to influence the formation of thunderstorms and foster high near surface temperatures. Therefore, we assume that the more general atmospheric deserts also have an influence on thunderstorms and high near surface temperature, as well as on dust transport simply due to their origin regions.
The present analysis focuses on tracking atmospheric deserts travelling from Northern Africa to Europe between May 2022 and April 2024, using the Lagrangian Trajectory Analysis Tool (LAGRANTO). We analyse the co-occurrence of atmospheric desert air with anomalously high dust aerosol optical depths or near surface temperatures, as well as lightning occurrence for the European domain (30°W to 60°E and 15° to 73°N). For this purpose, we use atmospheric and aerosol reanalysis data (ERA5 and EAC4) and lightning data from Blitzortung.org. We find that in almost the entire domain it is more likely that near surface positive temperature anomalies occur with atmospheric desert air present, than without. Similarly, anomalous values of dust aerosol optical depth are almost always tied to the presence of an atmospheric desert and in roughly 10–50% of instances when atmospheric desert air is present, it is accompanied by dust. We also investigate the vertical distribution of dust within the AD air mass. Lightning is more likely to happen close to the edge of atmospheric deserts, but also in their centre. While the former was expected from what is known from elevated mixed layers, the latter is surprising and indicates that atmospheric deserts do not inhibit thunderstorm formation in their centres via capping.
Heat, dust, and thunderstorms are often investigated independently, but our results clearly show that they all can be connected to atmospheric deserts. Understanding the relation of atmospheric deserts and the mentioned extremes is crucial for developing theories and better predictions of these events.
How to cite: Fix-Hewitt, F., Stucke, I., Zeileis, A., Stauffer, R., and Mayr, G. J.: Atmospheric deserts and their association with heat, dust andthunderstorm events, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-126, https://doi.org/10.5194/ems2026-126, 2026.
Spatially heterogeneous surface warming across continents is strongly governed by atmospheric circulation changes. Although long-term trends in upper-level atmospheric circulation have been identified, their contribution to regional warming hotspots remains unclear. In this paper, we use dynamical adjustment analysis to decompose the dynamical and thermodynamic components of long-term warming in observations and climate models. Our findings show that the observational warming is accelerating in eastern Europe, northwestern China, eastern Siberia, and western North America. While climate models broadly reproduce total warming trends in these hotspot regions, part of this agreement arises for the wrong reasons. In particular, model ensembles underestimate dynamics-induced warming in eastern Europe, northwestern China and eastern Siberia, but compensate for this with an overestimation of the thermodynamic component of warming. Conversely, climate models more accurately reproduce the dynamics-induced warming in western North America. To disentangle the underlying dynamical regime, we then adopt a complex network approach and 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. Climate models further project that the dynamics-induced warming 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 incorporate upper-level wind-field dynamics in regional surface temperature projections, particularly given the projected intensification of the tripole pattern under global warming.
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, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-591, https://doi.org/10.5194/ems2026-591, 2026.
Rossby wave packets (RWPs) organize large-scale energy transport in the atmosphere. The significance of this energy transport for atmospheric predictability and teleconnections has long been recognized. We here focus on RWPs along the midlatitude jet, which have received much attention as predictable precursors to high-impact weather events. More generally, these RWPs organize midlatitude weather systems and shape their climatological occurrence frequency and intensity. RWPs are frequently considered as physical entities identified by the Rossby-wave envelope. From this perspective, RWPs appear as features on a scale larger than that of the underlying troughs and ridges, i.e., they appear as features that live on scales larger than the synoptic scale. In particular, with resepct to predictability, a long-standing hypothesis by Lee and Held (1993) states that "the packet envelope should be more predictable than the individual weather systems, because the packet can remain coherent despite chaotic internal dynamics". Testing this hypothesis with ERA5 re-forecasts, we find that the RWP envelope does not exhibit this hypothesized higher predictability, at least when compared to the pattern of the underlying Rossby waves themselves, and until the end of the available lead time range of 10 days. This statistical result is substantiated by the examination of the underlying error-growth mechanisms. We will further provide a dynamics-based explanation of the counterintuitive result that the (seemingly) larger-scale envelope feature does not exhibit the expected higher predictability. Finally, we will conclude the presentation with a discussion of the role of the envelope perspective for predictability questions beyond the medium range.
How to cite: Riemer, M. and Gölz, L.: Do Rossby wave packet envelopes exhibit enhanced predictability?, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-634, https://doi.org/10.5194/ems2026-634, 2026.
The Mediterranean is a major cyclogenesis hotspot, where Eastern Mediterranean cyclones (MCs) play a central role in regional weather and climate. These systems are key drivers of precipitation and high-impact weather, including heavy rainfall and strong winds. However, their predictability remains limited due to complex topography and the interaction of multi-scale processes that are not fully resolved in numerical weather prediction (NWP) models.
This study investigates the dynamical controls on MC-related precipitation by linking the predictability of upper-level forcing to surface cyclone development and associated hazards. We analyze ~400 MCs over a 25-year period using ensemble reforecasts, with ERA5 as reference. Upper-level forcing is represented by potential vorticity (PV), while sea-level pressure (SLP) and precipitation characterize the surface response.
Forecast performance is evaluated using the feature-based SAL (Structure, Amplitude, Location) method, allowing a systematic object-oriented comparison of PV structures, cyclones, and precipitation across lead times. We present case studies to illustrate the evolving link between PV, SLP and precipitation, and climatology of objectively tracked and classified cyclones, spanning different dynamical regimes from baroclinic systems to thermal lows.
Our results reveal a clear link between the upper-level PV structures and the predictability of surface cyclones and precipitation. Regimes associated with non-linear wave breaking exhibit reduced predictability, highlighting specific sources of forecast uncertainty. Furthermore, links emerge between the forecast skill of PV and SLP and that of precipitation for early lead time. These findings provide new, quantitative insight into the processes governing MC predictability and offer guidance for improving forecasts of high-impact weather in the water-sensitive Eastern Mediterranean.
How to cite: Gens, T. S., Magaritz-Ronen, L., and Raveh-Rubin, S.: Predictability of Eastern Mediterranean Cyclones: A Systematic, Process-Based Analysis of Upper-Level Potential Vorticity and Precipitation Features, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-313, https://doi.org/10.5194/ems2026-313, 2026.
Due to the chaotic nature of the atmosphere, even with a perfect model, the lead time range of skillful weather forecasts (i.e., predictability) is limited and controlled by the level of initial (analysis) error. In several recent BAMS articles, the TC track forecast error is found to grow exponentially within 5 days lead time, thus an exponential growth of error development is assumed, based on this assumption, the tropical cyclone track forecasts are expected to be extended by one day per decade in Atlantic Ocean (ATL) while two days per 15 years in Western North Pacific Ocean (WNP). Now another question is raised: since there is no bound for an exponential growth, will the error grow unbounded? If not, what will the errors behave outside 5 days? Furthermore, what are the bound of the lead time ranges? Will the improvement be unbounded?
Due to the limitation of the linear assumption, the previous studies cannot reach the bounds. Here, building on those BAMS articles, namely, using the same data set, we re-estimate the error amplification rate and the initial error reduction rate in a nonlinear way by introducing a logistical function. Results for short lead times are found to be consistent with those found by the linear method, confirm the nonlinear method is adoptable. Then the limit of forecast improvement as well as the limit of forecast lead times can be estimated.
Take a 5 days’ forecast error that had been reached in 2021 in WNP as the largest acceptable TC track error, and supposing the initial position error will go down to 1km, the limit of forecast lead times will be 13.7 days in WNP and 15.5 days in ATL. While the limit of forecast improvement will be about 60km for a lead time of 1 day, and 150km for a lead time of 3 days, and 260km for a lead time of 5 days. These are hopefully to be achieved in 80 years for WNP while 100 years for ATL with current speed of technological progress.
How to cite: Zhou, F.: The Limit of Tropical Cyclone Track Predictabilities in the Northwest Pacific and Atlantic Oceans, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-144, https://doi.org/10.5194/ems2026-144, 2026.
Despite substantial progress over the past four decades, accurately predicting the spatiotemporal structure of the El Niño–Southern Oscillation (ENSO) remains a persistent challenge for dynamical models. While deep learning models have demonstrated improved prediction skills, their performances are constrained by biasesin climate models used for training and lack dynamic interpretability. Here we construct a novel hybrid model that integrates deep learning techniques into a dynamical model, enabling information exchanging during integration. Training on physical‐informed data, the model continuously adapts and improves forecasts, achieves unprecedented ENSO prediction skills, particularly in El Niño diversity and the spring predictability barrier. Moreover, as the hybrid model requires only a small volume of data by training on observations, it circumvents biases in climate models. Enhanced prediction skills arise primarily from improved representation of the leading feedbacks associated with ENSO. Our resultssuggest that training models with physical‐informed data is an effective approach for ENSO prediction.
KEY POINTS: 1)A hybrid model is constructed by integrating a deep learning model with a dynamical model.
2)Enhanced prediction skills arise primarily from improved representation of ENSO characteristics and the leading dynamical feedbacks associated with ENSO evolution.
3)The hybrid model requires only a small volume of training data.
The El Niño–Southern Oscillation (ENSO) is the Earth's largest source of year‐to‐year climate variability and greatly impacts global climate. Scientists have been trying to predictENSO's timing and strength, but traditional dynamical models still struggle to do this accurately. Deep learning models have shown promise, but they suffer from two major limitations: they rely on biased climate model data for training, and their predictions can be difficult to interpret physically. To address these issues, we developed a new hybrid model that integrates a deep learning module into a dynamical module, combining the strengths of both approaches. Our model makes more accurate predictions of ENSO events. The deep learning module is trained on physically informed data generated by the dynamical module, which reduces reliance on large volumes of observational data and minimizes errors from imperfect climate simulations. The improved prediction skill primarily arises from the model's enhanced ability to represent the key physical feedbacks that drive ENSO. This work demonstrates that integrating artificial intelligence with physical science leads to more accurate and more trustworthy climate predictions.
How to cite: Feng, J.: Achieving Explainable ENSO Prediction Using Small DataTraining, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-163, https://doi.org/10.5194/ems2026-163, 2026.
Despite progress in physical development and calibration, climate models still exhibit biases with respect to historical observations. As an alternative way to reduce them, run-time bias correction approaches have been developed, which consist in adding empirical tendency adjustment terms to the prognostic equations of some key physical variables. Although their ability to effectively reduce atmospheric circulation biases has been demonstrated, information is still missing regarding which method for estimating the adjustment terms is best suited for a given application. In this study, we implement a set of these methods in the atmospheric general circulation model LMDZ: nudging-based bias correction (the basis approach, a state-dependent version, and an iterative version), and the so-called climatological adaptive bias correction. Applying run-time bias correction on horizontal winds only, using these methods and varying some of their parameters, nine “bias-corrected versions” of the model are created. They are evaluated using aggregate scores of global mean errors in circulation, temperature, and precipitation, as well as mid-latitude atmospheric variability features (such as atmospheric blockings and stormtracks). A more regional perspective is also adopted, and a large region covering Europe and the North-Atlantic serves as a case study. It is found that, when evaluated on global aggregate scores, some versions outperform others. We also show that this does not prejudge the outcome on mid-latitude atmospheric variability features or at regional scale. No strict recommendation can be made regarding the optimal methodological choice, and great caution is advised. The choice should be guided by the model user’s needs and priorities.
How to cite: Champouillon, A.: Intercomparison of run-time bias correction methods in LMDZ_v6.3 , EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-363, https://doi.org/10.5194/ems2026-363, 2026.
Despite its successful performance compared to other U.S. NWS/NMC and later NCEP/EMC operational models, the Eta model was essentially frozen in 2002. This decision was made primarily due to the problem with step topography identified by Gallus and Klemp (2000); see the remarks by DiMego cited in Mesinger and Veljovic (2017, hereafter MV17). However, after about three years of EMC efforts dedicated to its planned replacement by NMM/GSI, the results of the EMC four-plus-month “parallel” test in 2006 showed verification scores favoring the Eta system (see MV17, Fig. 4).
Even so, the Gallus–Klemp problem needed to be addressed. This was accomplished by changing from step topography to “sloping steps,” now generally referred to as cut-cells (see MV17, Fig. 7). Regardless, the Eta continued to perform well; see the results of Veljovic et al. (2010), Mesinger and Veljovic (2013), and MV17, Fig. 11, the last of which discussed further in Mesinger and Veljovic (2020). In this later experiment, the Eta ensemble members driven by ECMWF (EC) members, although having about the same resolution for the first 10 days, achieved better scores for 250 hPa winds stronger than 45 m s⁻¹ than their EC drivers.
A puzzling byproduct of that experiment was that the Eta ensemble, when switched to use sigma, still achieved these 250 hPa wind scores better than their driver members, although to a lesser extent. The reasons for these results are addressed. Unique features of the Eta contributing to this advantage and addressed include its “fairly well-posed” (McDonald 2003) lateral boundary conditions (LBCs), specification of topography without smoothing, and the introduction of finite-volume vertical and slantwise advection.
New results presented here for the impact of the Eta LBCs show an advantage of the Eta LBCs over the ubiquitously used relaxation LBCs are giving more than twice as many times more accurate verifications of the upper tropospheric winds stronger than 45 m s⁻¹ than the relaxation LBCs. And a more accurate average equitable threat score adjusted to unit bias, ETSa.
The introduction of finite-volume vertical and slantwise advection compared to previous Lorenz-Arakawa centered finite-difference schemes enabled a more accurate placement of the foehn-type warming in the lee of Andes, in a challenging zonda downslope windstorm. In that experiment very steep topography of the Andes was used as generally done in the Eta without smoothing, customary in terrain-following models.
How to cite: Mesinger, F., Gomes, J., Jovic, D., and Veljovic, K.: What cut-cell Eta features additional to its intersecting the topography are responsible for its successful performance?, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-343, https://doi.org/10.5194/ems2026-343, 2026.
In this study, we compare the vertical tilt and potential vorticity (PV) structure of average and extreme extra-tropical cyclones (ETCs) in the Northern Hemisphere during the extended cold season (October--March) in ERA5 reanalysis. Enabled by a tracking method across pressure levels, the ETC vertical tilt is quantified using a novel two-component (directional and lateral) horizontal distance between the near-surface and upper-level ETC centres. The directional component of the tilt is parallel to the ETC travel direction at 850 hPa, while the lateral component is orthogonal to the ETC travel direction. During the ETCs life cycle, the typical tilt progresses from left and backwards leaning (negative directional and positive lateral tilt) to right and forward leaning (positive directional and negative lateral tilt). Compared to average ETCs, extreme ETCs exhibit an amplified tilt magnitude during the intensification phase and a change in the sign of the lateral tilt prior to the time of maximum relative vorticity.
Typically, studies that examine the vertical structure of PV in ETCs use the simplified approach of analysing the vertical profile of PV which is taken directly above the near-surface ETC location under the assumption the ETC is vertically aligned at the time of its maximum intensity, i.e. there is no vertical tilt. In our study, we challenge this assumption and demonstrates that neglecting the tilt of ETCs significantly underestimates the magnitude of potential vorticity associated with the ETC in the upper troposphere.
Furthermore, accounting for the tilted vertical structure, our study shows that average ETCs are associated with an upper-level positive PV anomaly, which is constant through the ETC lifecycle, while the PV intensifies from the bottom up. In contrast, extreme ETCs are characterised by an increasing magnitude of the upper-level PV anomaly, and a simultaneous intensification throughout the lower levels.
How to cite: Köhler, D. and Sinclair, V.: Differentiating average and extreme extra-tropical cyclones by their vertical tilt and potential vorticity structure, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-95, https://doi.org/10.5194/ems2026-95, 2026.
Serial cyclone clustering is commonly associated with intensified upper-level jet streaks and enhanced baroclinicity. While both diabatic processes and double-sided Rossby wave breaking have been proposed as explanatory mechanisms, their relative contributions remain incompletely understood. This study introduces a jet-streak-centered visualization technique to quantify contributions to cross-jet heating and to analyze the lifecycle of a jet streak that was pivotal during the development of the cyclone cluster consisting of the severe windstorms Dudley and Eunice over the North Atlantic in February 2022. The analysis relies on numerical simulations conducted with the Open Integrated Forecasting System developed by the European Centre for Medium-Range Weather Forecasts (ECMWF).
For the selected case study, the initial intensification of the jet streak along the North American East Coast appears to be primarily driven by diabatic processes. Specifically, latent heat release on the equatorward side and upstream of the jet streak maximum serves to strengthen the horizontal temperature gradient, thereby via the thermal wind law reinforcing the upper-level jet streak.
Furthermore, sensitivity experiments varying the magnitude of latent heat release demonstrate a significant impact on jet strength: a reduction in latent heat release (50% Lv) yields a substantially weaker jet streak, whereas an enhancement (150% Lv) results in a marginally stronger jet streak compared to the control run. The evolution of baroclinicity, diagnosed via the Eady growth rate, proves more complex, appearing to stem from an interplay between vertical wind shear and atmospheric stability. Under conditions of reduced latent heating, stability decreases, yet this does not offset the significantly weakened vertical wind shear. Conversely, with increased latent heating, stability is enhanced, acting to suppress baroclinicity despite the presence of strengthened vertical wind shear.
We conclude that latent heat release is the dominant mechanism driving the initial intensification of the jet streak during this February 2022 serial cyclone clustering event, indicating that diabatic processes play a central role in shaping the baroclinic environment of such cyclone clustering events.
How to cite: Batelaan, T. J., Weijenborg, C., and Steeneveld, G.-J.: The Role of Diabatic Processes in Jet Streak Intensification over the North Atlantic during a Serial Cyclone Cluster event encompassing storms Dudley and Eunice, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-454, https://doi.org/10.5194/ems2026-454, 2026.
The safety and performance of wind turbines depend on assumption about the wind they experience. This study examines whether those assumptions which are defined in the International Electrotechnical Commission (IEC) standard 61400-11 remain valid under typhoon conditions through analysis of Dual Doppler Radar measurements from a case study. The IEC standards include simplified representations of wind behaviour which is widely used within turbine design and load calculations. However, it is unclear if these assumptions are still applicable during typhoons conditions. A case study of Typhoon Haikui in the Western Pacific is presented. In late August 2023 the typhoon approached Taiwan from the east, crossed the southern part of the island before reaching the Formosa strait, it then crossed the strait and continued toward mainland China. As the typhoon passed over Taiwan, a dual Dopper radar system captured high-resolution wind measurements. This provides a unique opportunity to analyse the wind field of a nearby typhoon.
Using these observations, several wind field characteristics are examined and evaluated against the assumption used in the IEC standards. The assumptions include the logarithmic vertical wind profile, a constant shear exponent, prescribed gust characteristics and a spatially uniform wind field. The high spatial and temporal resolution of the dataset allows these assumptions to be examined throughout the evolution of the storm and across different spatial locations. The exploration of how these parameters vary relative to the proximity to the coastline of Taiwan, and the phase of the typhoon shows that the wind characteristics can be unsteady and inhomogeneous.
Preliminary analysis suggests that several wind field characteristics exhibit spatial and temporal variability during the typhoon, indicating that some of the simplified assumptions may not fully represent the wind behaviour during typhoon conditions. These findings contribute to an improved understanding of extreme wind feature and provide insight relevant for the risk assessment and design of wind turbines operating in typhoon-prone regions.
We thank Ørsted for making the data available and Smart Wind Technologies for their development of products and services related to this research2.
1International Electrotechnical Commission: Design Requirements, Wind Energy Generation Systems / International Electrotechnical Commission, International Electrotechnical Commission, Geneva, Switzerland, edition 4.0 edn., ISBN 978-2-8322-6253-5, 2019.
2 EU Patent 2877741: System and Method for Evaluating Wind Flow Fields using Remote Sensing Devices. John L. Schroeder, Brian D. Hirth, and Jerry G. Guynes. Issued March 28, 2019
How to cite: Chapman-Smith, K., Guo-Larsén, X., Fischereit, J., and Laier Brodersen, M.: Typhoon Haikui captured through Dual Doppler Radar measurements, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-301, https://doi.org/10.5194/ems2026-301, 2026.
There is growing evidence of the climate of Antarctica being impacted by global heating. For example, the Antarctic sea ice extent has sharply declined since around 2015 and has been at record or near record lows in most years since. This has potential to result in accelerated break up of key ice shelves, which would contribute to global sea level rise and have further impacts on local and regional climate in and around Antarctica. There have recently been some notable extreme events such as the atmospheric river event in March 2022, and exceptional melt events over the Antarctic Peninsula in the summer of 2019/20. Here, we present a new database of Antarctic meteorological extremes over a selection of key ice shelves, using simulations from four regional climate models (RCMs: RACMO2, HCLIM, MetUM and MAR), driven by the ERA5 reanalysis, examining surface temperature, precipitation, wind and surface pressure. In addition, we examine trends in the frequency of extreme events above specified thresholds, and spatial anomaly patterns over Antarctica that are commonly associated with extreme events over key ice shelves. The RCM simulations have been compared with station observations close to the ice shelves, and we developed regressions to estimate simulated values during periods when not all of the RCMs were available. The results of the database are compared with weather system drivers such as atmospheric rivers, storm tracks and blocking, as well as teleconnections such as the Southern Annular Mode, to determine links between these drivers and the occurrence of meteorological extremes over the ice shelves. Over most of the ice shelves covered, the frequency of extreme events has not shown a strong trend over the period, but there is evidence of some extremes, especially high temperature extremes, having increased in frequency since the mid-2010s over some of the ice shelves, which could be related to the sharp decline in Antarctic sea ice extent.
How to cite: Simpson, I., Hanna, E., Luu, L., Williams, R., Orr, A., and Jones, J.: A new database of Antarctic extreme weather events over key ice shelves and weather system drivers, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-653, https://doi.org/10.5194/ems2026-653, 2026.
The Madden-Julian Oscillation (MJO) is a prominent source of subseasonal-to-seasonal predictability in the tropics. Both observations and numerical simulations indicate that the MJO typically weakens when it propagates across the Maritime Continent, a phenomenon known as “the barrier effect”. However, numerical models often overestimate this effect, resulting in reduced prediction skill for MJO crossing events. Previous research has emphasized the influence of moisture structure in this deficiency. However, the dynamical structure of the MJO, which is essential for vorticity advection and generation, has received less attention.
This study investigates the dynamical characteristics of MJO events crossing the Maritime Continent using CESM1. Based on the criterion that the Real-time Multivariable MJO index (RMM) amplitude remains above 1 throughout phases 4 and 5, we identified 23 MJO events between 1997 and 2012 that successfully crossed the Maritime Continent. For each case, hindcasts were initialized with ERA-Interim during RMM phases 1 or 2, amounting to 197 dates. The model was also initialized with YOTC (Year of Tropical Convection) analysis during October 2008 and April 2010 for comparison. The model successfully reproduced the Maritime Continent crossing in 16 cases for at least one initialization date, amounting to 50 dates.
Comparison between successful crossing and blocked hindcasts reveals distinct differences in the vorticity field. Specifically, successful crossing events are characterized by a Rossby vortex to the west of the MJO convective center that exhibits a more compact zonal scale, despite having similar intensity to blocked events. In the lower troposphere, when the MJO center is over the Indian Ocean, the zonal scale of the Rossby vortex is approximately 3000 km, compared to 5000 km in blocked events. With a more compact structure, the low-level cyclonic vorticity generation, caused by the leading convective heating, pulls the Rossby vortex eastward more efficiently. Consequently, the MJO is less prone to the reduction of oceanic convection over the Maritime Continent, thereby increasing the probability of a successful crossing. Furthermore, compared with ERA-Interim, YOTC analysis exhibits a more compact dynamical structure as well as a higher fraction of crossing events.
These findings indicate that the horizontal spatial scale of the Rossby vortex is critical for MJO crossing the Maritime Continent barrier. Better initialized dynamical field can improve the model ability to capture MJO propagation across this complex region.
How to cite: Weng, L. and Lin, Y.: Influence of Rossby vortex zonal scale on MJO crossing Maritime Continent barrier, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-407, https://doi.org/10.5194/ems2026-407, 2026.
The diurnal cycle of convection over the Maritime Continent (MC) has long been hypothesized to act as a major barrier to the eastward propagation of the Madden–Julian Oscillation (MJO), yet the physical mechanisms responsible for this barrier effect remain incompletely understood. To investigate this problem, we use a regional numerical model that realistically reproduces the large-scale structure and evolution of an observed MJO event during boreal spring 2013, a case in which the MJO weakened substantially and eventually stalled over the MC. Two experiments are conducted to isolate the role of the diurnal cycle: a control simulation with the full diurnal cycle of insolation included (CTL), and a sensitivity simulation in which the diurnal cycle of solar forcing is removed (NO_DC). MJO propagation in these simulations is identified and tracked using a large-scale precipitation tracking framework, which is able to distinguish propagating from non-propagating events more effectively than the conventional Real-time Multivariate MJO index. Results show that in the NO_DC experiment, the absence of daytime insolation suppresses the development of strong afternoon convection and reduces precipitation over the major islands of the MC, thereby weakening the local convective barrier and allowing the MJO to propagate eastward more continuously. Further diagnosis based on the moist static energy budget indicates that enhanced MJO maintenance in NO_DC is associated with increased longwave radiative heating and reduced total advection, while the more persistent eastward propagation is linked to enhanced horizontal and vertical advection together with reduced longwave heating and surface latent heat flux ahead of the convective center. These results suggest that the impact of the diurnal cycle on MJO propagation operates through multiple thermodynamic pathways and that these processes differ across various parts of the Maritime Continent, highlighting the strong regional complexity of MJO propagation through this convectively active area.
How to cite: Zhou, X., Ray, P., Dudhia, J., and Hagos, S.: Role of Diurnal Cycle of Insolation on the MJO Propagationin the Maritime Continent, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-427, https://doi.org/10.5194/ems2026-427, 2026.
The increasing frequency and intensity of extreme precipitation events pose growing societal risks, underscoring the urgent need for effective early warning systems. Forecasting such events at subseasonal-to-seasonal timescales, however, remains a major scientific challenge. Utilizing Seasonal Forecast System version 5 from the European Centre for Medium-Range Weather Forecasts, here we show that introducing a total atmospheric energy proxy into forecasts substantially improves extreme precipitation prediction at subseasonal and longer timescales. This approach extends the effective forecast lead times from about one month by conventional methods to six months, and achieves more than tenfold increases in global prediction accuracy over the past two decades. The added predictive value of total energy has increased substantially in recent years, reflecting a strengthening relationship between total energy and extreme precipitation. These findings highlight the emerging energy signals that enhance predictability, offering promising opportunities for developing more reliable early warning systems in a warming future.
This study identifies three key advantages of introducing atmospheric total energy as a proxy for early warnings of extreme precipitation: (1) A substantial improvement in prediction skill at subseasonal and longer timescales. Incorporating total energy into forecast significantly enhances the accuracy of extreme precipitation prediction across regional and global scales. Compared with direct precipitation forecasts, total energy-based predictions yield up to a tenfold increase in hit rates for extreme precipitation days globally; (2) Increasing predictive value in recent years. The added skill from total energy has grown markedly since the 2010s, reflecting both a strengthened relationship between total energy and precipitation extremes and rising total energy levels under climate warming. The growing spatial coherence and intensity of large-scale extreme precipitation further amplify this signal; (3) Physical interpretability through energy budget analysis. A diagnosis of the total energy budget offers a physically grounded framework for identifying sources of predictability and model error, thus providing guidance for detecting the forecast limit and improving forecast systems.
How to cite: Zhang, T., Chen, J., Deng, Y., Yang, S., Chen, D., Zhu, J., and Cai, F.: Emerging energy signals advance early warnings of extreme precipitation, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-143, https://doi.org/10.5194/ems2026-143, 2026.
Extreme precipitation represents a major hazard in Europe, particularly in regions with complex terrain and strong land-sea contrasts such as the Alps and the Mediterranean. Here, we investigate synoptic-scale circulation patterns associated with extreme precipitation using simulations from the nextGEMS (Next Generation Earth Modelling Systems) high-resolution climate experiments at different horizontal resolutions.
Synoptic regimes associated with extreme precipitation events over Italy and surrounding regions are identified using Gaussian Mixture Model clustering applied to daily standardised anomalies of mean sea-level pressure and 500 hPa geopotential height. The resulting classification of days with extreme precipitation is used to analyse the occurrence and characteristics of precipitation extremes under different large-scale flow situations and to assess how these relationships depend on model resolution and the representation of deep convection.
The analysis reveals that dominant weather regimes are consistently represented across simulations with horizontal grid spacings between 4 and 9 km, indicating a robust representation of synoptic-scale variability. However, substantial differences emerge in the representation of regime-conditioned precipitation extremes. Higher-resolution simulations more realistically capture the intensity and spatial structure of extreme precipitation, particularly over complex Alpine terrain and along Mediterranean coastlines. These improvements are primarily associated with a limited number of circulation regimes characterised by strong moisture transport and favourable flow configurations for orographic lifting. Consequently, resolution-dependent differences in extreme precipitation are not uniform across all synoptic situations but are confined to specific large-scale regimes.
These findings highlight the value of combining circulation-regime diagnostics with kilometre-scale climate simulations to better understand the multi-scale processes controlling regional precipitation extremes and their sensitivity to model resolution and convective parameterizations.
How to cite: Klewinghaus, S., Gascón, E., Schemann, V., Vannière, B., and Vercauteren, N.: Using synoptic regimes to diagnose resolution effects on extreme precipitation in high-resolution climate simulations over complex terrain and coastal regions, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-247, https://doi.org/10.5194/ems2026-247, 2026.
The Yunnan-Guizhou Plateau (YGP) represents the steepest and most sophisticated terrain in China, as well as being highly susceptible to extreme meteorological disasters. The eastern YGP has a high incidence of regional extremely persistent heavy precipitation (REPHP). Hourly gridded precipitation data from May to July during 2019-2023 were used to define and study REPHP in eastern YGP. It was found that the REPHP events in the eastern YGP were mainly concentrated near the southern boundary and western mountainous areas. Two distinct high-incidence areas (HIAs) of REPHP were identified: the Plain-Hills HIA, situated on the southeastern windward slopes near the Nanling Mountains, and the Plateau-Mountain HIA, located on the western windward slopes near the Laowang Mountains. They mainly occurred from May to July, but especially in June. Influenced by local characteristics, the peaking time of diurnal variations differed between HIAs. ERA5 reanalysis data were used to investigate the synoptic patterns and their impacts in HIAs. The synoptic patterns in both HIAs were accompanied by the Western Pacific Subtropical High (WPSH). When the WPSH was located near 112°E, 16°N and there were southwest low-level jets (LLJs), shear line at 850 hPa and upslope wind would lead to REPHP over the Plain-Hills HIA. If WPSH extended to Beibu Gulf, the Plateau-Mountain HIA was controlled by the updraft generated by South Asia high (SAH), the trough at 500 hPa, shear line at 700 hPa and southerly LLJs. The Plain-Hills HIA features a more favorable convective environment than the Plateau-Mountain HIA, with higher most unstable convective available potential energy MUCAPE, stronger 0–3 km vertical wind shear, and higher precipitable water. Consequently, REPHP events in the Plain-Hills HIA typically exhibit a longer duration, stronger intensity and larger spatial extent.
How to cite: wan, J. and xu, X.: Spatiotemporal Characteristics and Associated Synoptic Patterns of Regional Extremely Persistent Heavy Precipitation in estern Yunnan-Guizhou Plateau, China, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-202, https://doi.org/10.5194/ems2026-202, 2026.
The southeastern Tibetan Plateau (SETP) is the preeminent summer heavy precipitation region within the Tibetan Plateau (TP). Heavy precipitation plays a critical role in regulating regional water resources, glacier mass balance, and ecosystem functions in the SETP. However, the large-scale circulation types and dynamics driving summer heavy precipitation in the SETP remain inadequately elucidated. Using the hierarchical clustering method, two distinctive atmospheric circulation patterns associated with heavy precipitation were identified: the Tibetan Plateau vortex type (TPVT, constituting 56.6% of the events) and the mid-latitude trough type (MLTT, 43.4%). A comprehensive examination of the two atmospheric circulation patterns reveals a clear nexus between the occurrences of summer heavy precipitation and positive vorticity anomalies, moisture convergence, as well as the southeastward displacement of the westerly jet core. Specifically, TPVT is linked to the generation of the TP vortex, which is triggered by the TP sensible heat. The formation of TPVT heavy precipitation is characterized by processes such as potential vorticity development and up-and-over moisture transport on the western TP. These processes drive the development of the TP vortex and its southeastward movement towards the SETP, which finally results in TPVT heavy precipitation. MLTT is associated with the mid-latitude circulation systems. A strong mid-latitude trough and ridge pattern drives the southward flow of cold air from middle and high latitudes to the SETP, converging with warm and humid air transported through the Indian summer monsoon and the westward-extended Western Pacific subtropical high. The interaction between mid-high latitude and subtropical air masses, along with their circulation patterns, leads to the MLTT heavy precipitation. This study advances our understanding of the complex mechanisms governing the summer heavy precipitation in the SETP, shedding light on critical meteorological processes in the region.
How to cite: Cao, D.: Two types of heavy precipitation in the southeastern Tibetan Plateau, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-749, https://doi.org/10.5194/ems2026-749, 2026.
This study uses reanalysis data, surface observations, and a Lagrangian trajectory model to compare the characteristics and moisture transport mechanisms of cold vortex and non-cold vortex rainstorms in Northeast China, North China, and the Jianghuai region under the influence of the Northeast Cold Vortex. The results show that: (1) The high-value area of rainstorms in Northeast China is located along the southern coast; in North China, it is in the southeast, with non-cold vortex rainstorms being more intense; in the Jianghuai region, cold vortex rainstorms are distributed along the Yangtze River, while non-cold vortex rainstorms are concentrated in the central-north and southeastern coast. Rainstorm frequency peaks in July in Northeast and North China, and in June in the Jianghuai region. The cold vortex significantly changes the rainstorm distribution in the Jianghuai region in June and August. All three regions show an upward trend in cold vortex rainstorm frequency, with the fastest increase in the Jianghuai region. (2) For cold vortex rainstorms in Northeast China, the southwest pathway contributes the most (40%), while non-cold vortex rainstorms are dominated by the southeast pathway (48%). In North China, both cold vortex and non-cold vortex rainstorms are primarily influenced by the southwest pathway (45% and 42%, respectively). In the Jianghuai region, the southeast pathway accounts for 62% of cold vortex rainstorms, compared to 46% for non-cold vortex rainstorms. (3) In Northeast China, the cold vortex easily triggers strong local cyclonic convergence, with moisture mainly from the eastern coast. In North China, the cold vortex introduces dry and cold air during rainstorms, reducing moisture but enhancing dynamic uplift through north-south wind convergence. In the Jianghuai region, the southward shift of the cold vortex interacts with the western Pacific subtropical high, leading to collisions between dry easterly currents and warm moist southwesterly jets, triggering convective instability and intensified precipitation.
How to cite: Hu, P.: Characteristics of Moisture Transport in Rainstorms in Different Regions of Eastern China under the Background of Warm-season Northeast Cold Vortex, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-750, https://doi.org/10.5194/ems2026-750, 2026.
Rainfall over Southeast Asia exhibits a pronounced diurnal cycle driven by complex land–sea interactions, particularly over the Maritime Continent, where mesoscale processes play a key role in shaping regional climate variability and predictability across spatial and temporal scales. Understanding how these processes respond to climate change remains challenging due to uncertainties in their representation in climate models and the complex interplay between thermodynamic and dynamical factors. This study evaluates the spatial and temporal characteristics of diurnal rainfall over the Maritime Continent and their projected changes during boreal summer and winter using six high-resolution regional climate model (RCM) simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX) Southeast Asia project. Evaluation against observations shows that the RCMs more accurately reproduce key features of present-day diurnal rainfall, including amplitude, peak timing, and coastal-to-offshore propagation, than their driving global climate models (GCMs), with the greatest added value in representing propagation over Maritime Continent islands. Future projections under the Representative Concentration Pathway 8.5 scenario for the late 21st century indicate minimal changes in diurnal phase timing over most land areas, but a widespread weakening of amplitude over the Maritime Continent in both seasons. The reduction is more pronounced in summer, accompanied by a weakening of coastal-to-offshore propagation. Inter-model agreement is robust over land areas of the Maritime Continent, increasing confidence in the projected weakening of the diurnal cycle. Analysis of physical mechanisms suggests that both reduced surface specific humidity and weakened surface wind convergence contribute to the suppression of the diurnal rainfall peak, with thermodynamic components dominating over Sumatra and dynamic components influencing more pronounced over Borneo. These findings highlight the importance of coupled circulation–moisture processes in shaping future changes of the diurnal rainfall cycle and demonstrate the added value of high-resolution regional modeling for advancing understanding of mesoscale meteorology and climate change in regions with complex land–sea interactions.
How to cite: Huang, W.-R., Ngai, S. T., and Chiang, T.-Y.: Simulation and Projection of Diurnal Rainfall over the Maritime Continent Using High-Resolution CORDEX-SEA Simulations, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-117, https://doi.org/10.5194/ems2026-117, 2026.
Pressure vertical velocity (ω = Dp/Dt), where Dp/Dt stands for material derivative, is commonly approximated from the geometric vertical velocity (w=Dz/Dt) as ω ≈ -ρgw, which invokes the hydrostatic relation ∂p/∂z ≈ -ρg together with the additional assumption that local pressure tendency and horizontal pressure advection terms are negligible at planetary and synoptic scales. Using global simulations with the Icosahedral Nonhydrostatic model, we show that the horizontal pressure advection term can be relatively large in comparison with the the vertical pressure advection at planetary-to-synoptic scales in regions of strong jets such as in the winter stratosphere, contradicting the conventional assumption ω ≈ -ρgw. We further show that the horizontal and vertical pressure advection terms are predominantly out of phase with each other, so that their comparable amplitudes lead to substantial cancellation. As a consequence, ω can be suppressed or amplified at large scales relative to the -ρgw diagnostic, despite the validity of the hydrostatic balance. Scale diagnostics indicate that the large-scale enhancement of the horizontal pressure advection arises from interactions between the mean flow and Rossby waves. They also suggest a substantial ageostrophic component within otherwise predominantly geostrophic large-scale motions. It is hypothesized that the generation of these ageostrophic winds is related to the ubiquitous jet streaks and curvature of the polar night jet, and thus, that enhanced horizontal pressure advection is likely a general feature of any jets. From an energetic perspective, these advection terms correspond to compensating contributions of pressure-gradient work in different directions. Consequently, ω behaves more like the net pressure gradient work, rather than a direct measure of vertical motion.
How to cite: Chen, J., Vasylkevych, S., Žagar, N., and Hohenegger, C.: On the interpretation of the pressure vertical velocity, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-16, https://doi.org/10.5194/ems2026-16, 2026.
Accurate prediction of the rapid intensification (RI) of tropical cyclones (TCs) remains a major operational and scientific challenge. A primary source of forecast uncertainty lies in the representation of turbulent mixing processes within the planetary boundary layer (PBL), which critically regulates the vertical transport of moisture and heat into the storm core. This study investigates this fundamental issue through high-resolution numerical simulations of Typhoon Yagi (2024). We demonstrate that the vertical profile of turbulent mixing, rather than its magnitude alone, is a decisive control on RI efficiency. Our analysis reveals that, in contrast to PBL schemes which produce excessive or insufficient mixing, the Bougeault–Lacarrère (BouLac) scheme uniquely promotes RI by generating a distinct peak in eddy diffusivity for moisture (approximately 200 m² s⁻¹) within the mid-to-upper boundary layer. This peak effectively confines and concentrates moisture, creating a localized reservoir. This process, which we term "moisture pre-concentration," is pivotal. The pre-concentrated moisture is then efficiently tapped and transported upward by the storm's already well-organized secondary circulation. This coordinated transport fuels robust latent heat release in the core, directly supporting the development of a strong warm core and a rapid pressure fall. Sensitivity experiments systematically modifying the moisture diffusivity (Kq) value within the BouLac framework reveal a non-monotonic response of TC intensity to mixing strength. A key finding is that, provided a sufficiently high moisture concentration is achieved via the "pre-concentration" mechanism, even experiments with substantially reduced bulk moisture transport can generate RI and high lifetime maximum intensity. This underscores that the spatial organization and vertical distribution of boundary layer moisture are more critical for RI onset than the total moisture abundance. Conversely, excessive diffusion (very high Kq) leads to vertical dilution of moisture, stifling intensification, while insufficient mixing fails to organize the moisture reservoir. Moisture-budget diagnostics confirm that RI efficiency is maximized when turbulent mixing primarily acts to organize low-level moisture for coordinated convective uplift, rather than merely strengthening the secondary circulation itself. Ultimately, these findings advance the mechanistic understanding of TC intensification. They emphasize that accurately resolving the vertical structureof PBL turbulent mixing, and its role in preconditioning the moisture field, is paramount for improving the physical basis and skill of future RI forecasts.
How to cite: Chen, S. and Wang, S.: Moisture Pre‐Concentration in the Boundary Layer: A Key Mechanism for the Rapid Intensification of Simulated Super Typhoon Yagi (2024) , EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-39, https://doi.org/10.5194/ems2026-39, 2026.
In the summer of 2023, North China experienced a severe and extreme heatwave that lasted for longer than the heatwaves occurring in other areas during this period and longer than any other North China heatwave between 1959 and 2023. During the event, an anomalous long-lived anticyclone dominated the North China region, which formed an extreme heatwave that persisted for more than 20 days. This long-lived anticyclone belonged to a Rossby wave train that originated in the Atlantic and propagated eastward to the East Asian coast. Although the Indian Ocean, Pacific Ocean, and Atlantic Ocean all experienced anomalous heating in 2023, the Atlantic SST anomalies played a dominant and decisive role in the extreme North China heatwave. Both observations and numerical simulations demonstrated a close relationship between Atlantic SST warming and the anomalous anticyclone and heatwaves in the region of North China, a relationship that was not observed or simulated for other oceans.
Atlantic SST warming in the summer of 2023 has a positive contribution to the North China heatwave. Whether there are other factors that contribute to the North China heatwave in 2023 is still unknown. The Atlantic SST warming can indeed provide a necessary anomalous anticyclone and lead to a persistent heatwave event. But other factors, such as urban heat islands, irrigation, may enhance the intensity of the heatwave of 2023 in North China, which needs further study. Moreover, the North Atlantic is experiencing a warming trend owing to global warming. Extreme warming of the North Atlantic in the summer of 2023 was likely caused by both global warming and natural variability. However, the relative contributions of anthropogenic activity and natural variability to North Atlantic warming and therefore the North China heatwave of 2023 remain unknown and require further study.
How to cite: Feng, J.: Role of North Atlantic warming in the extremely hot summer of 2023 in North China , EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-71, https://doi.org/10.5194/ems2026-71, 2026.
Precipitation forecasting remains challenging due to the complexity of its driving mechanisms and model limitations in resolving short temporal scales and subgrid processes. This study provides a comprehensive assessment of the performance of the Application of Research to Operations at Mesoscale (AROME) model in forecasting precipitation over mainland Portugal, using observations from a network of automatic weather stations for the period 2022–2023. Forecast skill is evaluated using a combination of categorical metrics derived from contingency tables and spatial verification approaches, enabling a multi-scale analysis of model performance. Results reveal a decrease in model skill with increasing precipitation thresholds. However, model performance improves for longer accumulation periods and when evaluated over larger spatial neighbourhoods, highlighting the importance of phase errors. To identify skilful predictors of heavy precipitation events, convective conditions were analysed during two illustrative extreme events in the Douro (Northern Portugal) and Alentejo (Southern Portugal) wine regions. Thunderstorm diagnostic parameters derived from the AROME model show good agreement with observed lightning activity, demonstrating skill in identifying favourable conditions for deep convection. Additionally, the consistency across forecast lead times suggests that these indices can support early identification of convective activity. These findings highlight the potential of combining precipitation forecasts with thunderstorm diagnostic parameters to improve operational early warning systems and the implementation of suitable risk reduction measures.
Acknowledgements: The authors acknowledge National Funds by FCT – Portuguese Foundation for Science and Technology, under the projects UID/04033/2025: Centre for the Research and Technology of Agro-Environmental and Biological Sciences (https://doi.org/10.54499/UID/04033/2025) and LA/P/0126/2020 (https://doi.org/10.54499/LA/P/0126/2020). Project WATERKNOW – Infraestrutura de Conhecimento Geoespacial para a Gestão Inteligente dos Recursos Hídricos (NORTE2030-FEDER-01392400)
How to cite: Cruz, J., Belo-Pereira, M., Fonseca, A., and A. Santos, J.: Performance of the AROME Model for Forecasting Heavy Precipitation Events in Portugal, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-173, https://doi.org/10.5194/ems2026-173, 2026.
Amid growing concerns about the impacts of climate change on extreme events, estimating future changes in extreme wind speeds has become increasingly important for wind-resistant design. Regions such as Japan are affected by multiple types of strong wind-generating systems, including tropical cyclones and extratropical cyclones, which complicates the assessment of wind speed extremes. Despite this complexity, relatively few studies have comprehensively evaluated future changes in wind speed extremes in such multi-hazard environments.
In this study, we assess future changes in extreme wind speeds over Japan using large-ensemble climate model simulations. To ensure a robust evaluation of rare and high-impact events, we employ a dynamically downscaled dataset with a horizontal resolution of 5 km (d4PDF_5kmDDS_JP), derived from the Database for Policy Decision making for Future climate change (d4PDF). The dataset consists of multiple ensemble members, including 60-year historical simulations as well as future climate experiments under +2°C and +4°C global warming conditions. This large ensemble framework enables a statistically stable estimation of extreme wind characteristics.
Extreme value distributions of wind speed are estimated for each experiment and subsequently bias-corrected using surface observation to improve their reliability. Based on these corrected distributions, changes in wind speeds corresponding to specific return periods are quantified and compared across different warming experiments.
The results indicate that, in some regions of Japan, the 50-year return-period wind speed increases by approximately 10% under the +4°C warming experiment relative to the historical experiment. Further analysis suggests that the projected increase in extreme wind speeds is primarily attributable to enhanced wind intensity associated with tropical cyclones, rather than changes in other synoptic-scale systems.
These findings provide important insights into the future behavior of extreme winds in a multi-hazard environment and offer a practical basis for incorporating climate change considerations into wind-resistant design in Japan, particularly through the adjustment of design wind speeds and safety margins.
How to cite: Kitano, Y., Ohba, M., Soda, N., Hattori, Y., and Ishikawa, T.: Future Changes in Extreme Wind Speeds over Japan Based on a Large-Ensemble Climate Dataset, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-181, https://doi.org/10.5194/ems2026-181, 2026.
How to cite: Chen, J., Žagar, N., Vasylkevych, S., Sielmann, F., Lunkeit, F., Neduhal, V., and Holube, K.: MODES: advancing wave-space diagnostics for global weather and climate models, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-232, https://doi.org/10.5194/ems2026-232, 2026.
Tropical cyclone (TC) is one of the most severe natural disasters in terms of human casualties and economic losses. Hadley circulation (HC), a dominant thermally driven meridional overturning circulation over tropics, has a prominent impact on TC activities. Previous study reveals that the expansion of boreal winter regional HC over western Pacific (WPHC) contributes to the increasing frequency of succeeding summer landfalling TC (LTC) in China. Here, we find that their relationship is nonstationary and experiences a marked interdecadal change around the mid-1990s, with the connection being weak before but significant after. The enhanced influence between them in recent decades is manifested by enhanced responses of summer sea surface temperature (SST), precipitation, and winds anomalies over tropical Pacific to the meridional movement of the preceding winter northern WPHC edge (WPHCE). Stronger climatological mean precipitation and trade winds strengthen the wind-evaporation-SST feedback over the subtropical North Pacific after the mid-1990s. As such, the winter WPHCE-related subtropical anomalous signals can more efficiently propagate to the deep tropics and then change the following summer LTC-favorable climate conditions over the tropical Pacific via positive air-sea interaction, thus leading to an enhanced impact of the WPHCE variation on LTC activity during recent decades. Besides, an increased standard deviation of the WPHCE variation after the mid-1990s may also partially contribute to this recent stronger WPHCE-LTC relationship. The results from this study emphasize the increasingly importance of the WPHC expansion for LTC activity over China, which calls for more attention to be paid to the WPHCE variation for LTC prediction.
How to cite: Huang, R., Hu, S., Chen, S., Chen, W., Wang, Z., Aru, H., and Peng, D.: Recent Enhanced Impact of the Regional Hadley Circulation Expansion over Western Pacific on Increasing Frequency of Landfalling Tropical Cyclone, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-252, https://doi.org/10.5194/ems2026-252, 2026.
Regional heat extremes are intensifying under global warming, yet their evolution reflects the combined influence of anthropogenic forcing and internal climate variability. Here we investigate long-term changes in temperature extremes across South Korea using daily observations from 60 weather stations during 1974–2023. A non-stationary Generalized Extreme Value (GEV) framework incorporating global mean surface temperature (GMST) as a covariate reveals clear non-stationary behavior in both summer and winter extremes across event durations of 1–15 days. Winter cold extremes have weakened markedly, accompanied by a broadening of temperature distributions and a reduced frequency of severe cold events, indicating a systematic decline in cold-air outbreaks. In contrast, summer extremes exhibit greater societal relevance, with tropical night events showing the strongest sensitivity to global warming. These events have increased rapidly in both frequency and persistence, particularly along the west and south coasts, where enhanced moisture availability and elevated nighttime temperatures amplify heat stress. This intensification is likely linked to the strengthening of the North Pacific Subtropical High and warming of surrounding seas, which together enhance moisture transport and suppress nocturnal cooling over the Korean Peninsula.
Despite the persistent warming trend, heatwave activity exhibits pronounced decadal variability. A relative lull from the late 1990s to the early 2010s (period 1, P1) was followed by a rapid resurgence thereafter (period 2, P2). This shift is associated with changes in the North Atlantic Oscillation (NAO), whose planetary-scale teleconnections modulate atmospheric circulation over Northeast Asia. Positive NAO phases strengthen anticyclonic circulation over the Korean Peninsula, enhancing subsidence and surface warming. During P1, the NAO weakened with reduced interannual variability, likely linked to tropical Pacific forcing. In contrast, during P2, it strengthened, potentially driven by Atlantic forcing in conjunction with a phase shift in tropical Pacific variability. These results demonstrate that regional temperature extremes arise from the interplay between externally forced warming and internally generated climate variability, underscoring the importance of accounting for both processes in future climate risk assessment and adaptation.
How to cite: Ryu, J. H. and Kang, S. L.: Nonstationary Temperature Extremes in South Korea: Roles of Global Warming and Large-Scale Climate Variability, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-256, https://doi.org/10.5194/ems2026-256, 2026.
Abstract:From 23 to 29 July 2025 (referred to as "25.7"), extraordinary heavy rainfall occurred in Beijing and other North China areas. Based on data from Automatic Weather Stations in the Beijing-Tianjin-Hebei region, multi-band networked radars, Beijing Doppler weather radar, ERA5 reanalysis, Beijing RISE 100-metre resolution gridded analysed wind field, and Beijing RMAPS- NOW 1km resolution gridded data, this paper analyses the characteristics of rainfall stages, fine-scale convective features, and the causes of extreme heavy rainfall. The results showing: (1) The '25.7' heavy rain event was characterised by a long duration, large cumulative rainfall, concentrated heavy precipitation in the northern mountainous areas often occurring at night, local and extreme characteristics, and severe disaster impacts. The rainfall in Beijing in late July this year was 203.8% higher than the average for the same period in previous years, ranking fifth in history. (2) This torrential rain occurred in late July against a relatively stable large-scale circulation background, with the Subtropical-High （SH） pressure significantly located westward and northward and stronger than usual. Tropical systems were active on the southern side of the SH, and the easterly winds on the northern side of the typhoon strengthened, facilitating the transport of water vapour inland. The southerly moisture flux on the Beijing-Tianjin-Hebei Plain showed significant moisture flux convergence at the front, with precipitable water exceeding 70 mm and low-level warmth anomalies, providing a high-temperature, high-humidity, and high-CAPE environment for the extreme rainfall. (3) The rainfall in Beijing lasted for 147 hours, with four stages corresponding to the periphery of the SH, a significant northward shift, a slight southward retreat, and the influence of the northern upper-air trough and cold air. The first and fourth stages had widespread heavy rain, but the overall intensity was not strong; the second and third stages had rainfall that was weak in many areas but strong in spots, with locally extreme cumulative rainfall, and high disaster potential. On the 26th, heavy rain mainly occurred at altitudes of 200–600 m, whereas on the 27th, heavy rain mostly occurred below 300 m. (4) On the nights of the 26th and 27th, the windward slopes in the northern mountainous areas experienced near-surface convergence of southerly and south-easterly winds, and were located at the exit region of a locally enhanced low-level jet (LLJ). This resulted in strong convergence and vertical upward motion, favourable for the continuous triggering of backbuilding convection near the foothills, creating a training effect. The strongest convergence at the LLJ exit caused extreme rainfall. The convective latent heat release in the upper cloud significantly enhanced the vertical upward motion to over 10 m, providing a positive feedback for the occurrence of extreme rainfall.
How to cite: Lei, L.: Preliminary Analysis of Fine-Scale Characteristics and Formation Cause of Beijing "25·7" Extreme Rainstorm, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-334, https://doi.org/10.5194/ems2026-334, 2026.
In the second decade of January 2020, beginning on 12 January, a case of long-lasting continuous fog occurred in most regions of Serbia. On 17 January, widespread fog was also observed at some stations in Croatia, Bulgaria, Romania, Hungary, and Slovakia. This fog event indicated the presence of a broad air mass whose characteristics favored the formation of regional fog. A high-pressure system with a warm core at upper levels, centred over western and central Europe, caused extremely stable weather with a strong temperature inversion that persisted throughout the fog period. Mean sea level pressure over regions of Serbia exceeded 1027 hPa during the event. The effects of ECMWF model initial and boundary conditions on simulations with the regional Eta model were examined. The ECMWF model forecast starting at 12 UTC, compared to the forecast starting at 00 UTC on 12 January, was slightly better in terms of fog duration and location, however, in both forecasts the fog dissipated after a few hours. Experiments with improved horizontal and vertical resolutions of the Eta regional model nested into the ECMWF model did not improve the forecast of this fog event. A series of ensemble simulations with the Eta model was conducted to investigate the effects of physical parameterizations on the fog forecast. The success of the fog forecast results was evaluated using surface and upper air fields. In these forecasts, fog occurrence was defined based on a liquid water content threshold (0.05 g m⁻³), which was converted to visibility using the Kunkel equation.
How to cite: Stojanović, S. and Veljović Koračin, K.: A forecast improvement of a widespread fog event using ensemble simulations, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-402, https://doi.org/10.5194/ems2026-402, 2026.
Most of the northern-hemispheric, midlatitude cyclones develop, propagate, and decay within the storm tracks of the North Atlantic and the North Pacific. The variability within these storm tracks, along with associated blocking near their downstream end, governs a large part of the climate and weather extremes of the northern-hemispheric midlatitudes. Dynamically, the storm tracks are a coupled jet-eddy system: synoptic-scale Rossby waves and associated surface pressure systems (the ‘eddies’) propagate and evolve along the midlatitude jet. At the same time, the jet is accelerated by momentum fluxes of the eddies, hence the notion of the midlatitude jet as an ‘eddy-driven’ jet. Accurate diagnosis of this coupled storm-track dynamics remains central to understanding midlatitude variability, extremes, predictability, and climate change responses.
Traditional definitions of ‘jet’ and ‘eddies’ by spatio-temporal filtering of the underlying physical fields do not provide a clear separation between the background jet and the eddies, which limits physical interpretation on a conceptual level. More recent developments based on adiabatic re-arrangement of potential-vorticity contours, so-called zonalized background states, provide truly eddy-free background states and associated finite-amplitude wave activity to describe the eddies. Zonalized background states, however, inherently exhibit zonal symmetry, which limits their applicability to (localized) storm-track dynamics. A recent extension called ‘rolling zonalization’ allows for zonal variability of the background jet but provides only limited control over the desired separation of spatio-temporal scales.
In this contribution, we introduce a filtering method that provides full control of the spatio-temporal characteristics in the definition of an eddy-free background state. Challenges and solutions to defining finite-amplitude wave activity metrics associated with such a background are discussed. Arguably, the new framework enables a local perspective on storm-track dynamics while retaining many of the conceptual and theoretically appealing features of the zonally symmetric finite-amplitude wave-activity framework. We conclude with an illustration of first applications to describe storm-track characteristics on different time scales and muse on the prospects of the new framework to advance our understanding of storm-track dynamics.
How to cite: Riemer, M. and Hauth, E.: Defining zonally varying, eddy-free jets to diagnose storm-track dynamics, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-629, https://doi.org/10.5194/ems2026-629, 2026.
Compound extreme events have broader and more significant impacts on natural and social environments compared with individual occurrences. To this end, detection, and quantification of changes in the compound extreme events under a warm climate are important for making reliable risk projections and for understanding changes in compound extremes. This study quantified the characteristics of compound events based on i) empirical approach, and ii) quantile-based approach using both observed (1964–2014) as well as dynamically downscaled climate model data (2025–2075) for select locations in the United States. Compound events were defined based on the combination of temperature and precipitation (cold-wet, cold-dry, warm-wet, warm-dry) using 25% and 75% thresholds of temperature and precipitation. The empirical approach for the analysis of compound extreme events was executed through counting the number of compound extreme events on annual and seasonal scale and evaluating their trends for both the historical and the future time periods. Trend analysis shows increasing trends of warm-wet events for future climate conditions as compared to the historical period during both Representative Concentration Pathways (RCP) scenarios (4.5 and 8.5) with marked increase during RCP 8.5 scenario. Quantile regression method was used to detect the changes in conditional probabilities of compound extreme events. Results show that conditional trends of upper quantiles/tails have increased for warm-wet events and lower quantiles have increased for cold-wet events as compared to mean trends indicating that both warm and cold dominated compound extreme events are becoming more severe. Results from this study provide better understanding of the changes in compound events.
How to cite: Dhakal, N. and Werth, D.: Empirical and quantile-based analysis of compound extreme events, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-742, https://doi.org/10.5194/ems2026-742, 2026.
In the Asia-Northwest Pacific region, tropical cyclones (TCs) and mid-latitude troughs act as key atmospheric circulation systems, and their interaction significantly influences regional circulation patterns. This study employs statistical analysis and numerical experiments to reveal the influence of TCs over tropical western Pacific on the East Asia mid-latitude trough (EAMT).
Statistical analysis was conducted by using historical data including the NCEP FNL reanalysis data and JMA TC best track data from June to August between 2001 and 2020. Results indicate that TCs activities can drive the EAMT line to shift northwestward, while simultaneously expanding its north-south extension range and intensifying its strength. The remotely induced geopotential height (HGT) anomalies by TCs serves as a key reason for EAMT location changes, with the EAMT tending to move away from regions exhibiting positive HGT anomalies.
Numerical experiments take TC Maria (2018) as a case study. A control experiment and a TC-removed experiment were carried out with WRF model. Results indicate that TC Maria mainly caused stronger negative HGT anomalies on west side of the EAMT line. When the result obtained by subtracting the HGT anomalies on the east side of the EAMT line from that on the west side was positive (negative), the corresponding EAMT line moved eastward (westward). This indicates that the remote anomalous HGT induced by TC Maria serves as a key factor driving the zonal movement of the EAMT, which confirms the result of the statistical analysis. Reasons for the EAMT zonal movement lies in that TC Maria first induced anomalous cold advection in the mid-latitude regions of the East Asia-Northwest Pacific, which then led to an anomalous decrease in HGT within the EAMT region under the constraint of hydrostatic equilibrium. Since the EAMT line tends to move toward regions with stronger anomalous negative HGT, the TC induced HGT anomalies ultimately resulted in the zonal movement of the EAMT line.
Results of this study provide evidence that remote disturbances induced by TC activities in the tropical oceans can affect weather circulations in the midlatitudes.
How to cite: Wang, T., Wang, J., Huang, H., Gu, S., and Jiang, C.: How Tropical Cyclones Over Tropical Ocean Affect Mid-Latitude Trough, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-329, https://doi.org/10.5194/ems2026-329, 2026.
During the Meiyu season in China, in addition to the continuous systematic precipitation typically triggered by the stationary shear of the Meiyu front, there are also strong precipitation events caused by other types of weather systems, among which is warm shear-type precipitation. Using multi-source observational data from the Integrative Monsoon Frontal Rainfall Experiment (IMFRE-II) in 2020, an analysis was conducted of a strong precipitation event occurring in the middle and lower reaches of the Yangtze River from June 27th to 29th, 2020. The results indicate that: (1) This rainstorm process was a warm shear-type precipitation influenced by the eastward movement of the Southwest China vortex under the background of the Northeast China cold vortex. The peak of precipitable water vapor (PWV) occurred approximately 1-2 hours earlier than the peak of heavy precipitation. (2) Strong southwest low-level jets (exceeding 30 m·s-1) intersected with the cold air from North China in the middle reaches of the Yangtze River, generated the warm shear line on the left side of the low-level jet exit. The rainstorm area was located on the south side of the shear line, with a deep upward motion zone present, providing dynamic lifting conditions for heavy precipitation. (3) The South China Sea provided the maximum water vapor supply, and moisture transport formed a significant moisture convergence zone in the middle and lower reaches of the Yangtze River. CAPE values at Yichang station reached up to 1806 J kg−1, and pseudo-equivalent potential temperatures (θse) exceeded 355 K on June 27th, indicating vigorous convection development and providing strong thermal conditions for heavy precipitation. It is hoped to deepen the forecasters' understanding of the formation mechanism of such rainstorm and play a positive role in improving the extreme precipitation forecast level.
How to cite: Yang, H.: Analysis of the warm shear-type rainstorm process in the middle reaches of the Yangtze River influenced by the Northeast China cold vortex and the Southwest China vortex, EMS Annual Meeting 2026, Utrecht, Netherlands, 6–11 Sep 2026, EMS2026-52, https://doi.org/10.5194/ems2026-52, 2026.
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