Articles | Volume 7, issue 2
https://doi.org/10.5194/wcd-7-717-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-7-717-2026
© Author(s) 2026. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
08 May 2026
Research article |
| 08 May 2026
| 08 May 2026
Transient flow patterns of an annular-like stratospheric polar vortex
Huw C. Davies
Institute for Atmospheric and Climate Science, ETHZ, 8092 Zurich, Switzerland
Michael A. Sprenger
CORRESPONDING AUTHOR
Institute for Atmospheric and Climate Science, ETHZ, 8092 Zurich, Switzerland
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Anna Kuhn, Chenhui Jin, Elizabeth Ritchie, and Michael Armand Sprenger
EGUsphere, https://doi.org/10.5194/egusphere-2026-4836, https://doi.org/10.5194/egusphere-2026-4836, 2026
This preprint is open for discussion and under review for Weather and Climate Dynamics (WCD).
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We apply a clustering approach to analyze winter jet stream variability over Australia, defining five jet configurations. We find high variability, especially in the longitudinal jet maximum. Patterns of vertical motion show the strongest ascent south of the jet maximum, coinciding with enhanced precipitation. Extreme precipitation events for six Australian capital cities are linked to either a strong or weakened jet stream, highlighting the important role of the jet in driving those events.
Stefania Gilardoni, Annachiara Bellini, Paolo Bonasoni, Henri Diémoz, Christian Gencarelli, Angela Marinoni, Eros Mariani, Luigi Mazari Villanova, Bruno Neininger, Mattia Perilli, Michael Sprenger, and Francesco Petracchini
Atmos. Chem. Phys., 26, 11135–11152, https://doi.org/10.5194/acp-26-11135-2026, https://doi.org/10.5194/acp-26-11135-2026, 2026
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This study presents the first high-time-resolution aerosol data collected from the Testa Grigia Observatory (3,480 m) in the Italian Alps, from 2021 to 2023. We identified three transport pathways: Saharan Dust Events (SDE), which occurred with a frequency of 6 %, regional and long-range transported pollution (28 %), and clean air from the free troposphere. The timing of SDE, observed mainly in spring, and the mixing of dust particles with black carbon, enhance SDE impact on snow melting.
Matthias Röthlisberger, Michael Sprenger, Urs Beyerle, Erich M. Fischer, and Heini Wernli
Weather Clim. Dynam., 7, 1363–1384, https://doi.org/10.5194/wcd-7-1363-2026, https://doi.org/10.5194/wcd-7-1363-2026, 2026
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This study investigates yearly heat extremes simulated with the global climate model CESM2. A trajectory-based method is used, which allows quantifying the contributions to temperature anomalies from advection, subsidence, and diabatic heating. The results show that the magnitude of CESM2 heat extremes agrees fairly well with ERA5 reanalyses, but it is often
for the partly wrong physical reasons.
Ming Hon Franco Lee, Hanna Joos, Heini Wernli, Richard Forbes, and Michael Sprenger
EGUsphere, https://doi.org/10.5194/egusphere-2026-4184, https://doi.org/10.5194/egusphere-2026-4184, 2026
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Turbulence near jet streams modifies the atmospheric flow, but there is limited research on the underlying mechanism. In this study, we infer this feedback by tracing the change in potential vorticity. We use an analytical framework to explain the systematic changes caused by turbulence in a numerical simulation of a jet stream. A typical tripolar pattern appears repeatedly, and it is highly related to the coherence of the jet. The improved understanding may help advance weather forecasts.
Ellina Agayar, Moshe Armon, Michael Sprenger, and Heini Wernli
Nat. Hazards Earth Syst. Sci., 26, 3025–3043, https://doi.org/10.5194/nhess-26-3025-2026, https://doi.org/10.5194/nhess-26-3025-2026, 2026
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This study investigates the hydrometeorological features of the major floods of 2008, 2010, and 2020 in western Ukraine. All cases were linked to upper-level potential vorticity (PV) anomalies. We also conducted a climatological analysis of PV structure associated with 22 summer heavy precipitation events (2000–2022), highlighting their key role in determining the location and intensity of flood-inducing rainfall events in the Carpathians.
Alexander Pietak, Langwen Huang, Luigi Fusco, Michael Sprenger, Sebastian Schemm, and Torsten Hoefler
Geosci. Model Dev., 19, 3893–3922, https://doi.org/10.5194/gmd-19-3893-2026, https://doi.org/10.5194/gmd-19-3893-2026, 2026
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As meteorological models grow in complexity, the volume of output data increases, making compression increasingly desirable. However, no specialized methods currently exist for compressing data in the Lagrangian frame. To address this gap, we developed psit, a pipeline for the lossy compression of Lagrangian flow data. In most cases, psit achieves performance that is equivalent or superior to non specialized alternatives, with compression errors behaving similar to measurement inaccuracies.
Marius Rixen, Praveen Pothapakula, Michael Sprenger, Christian Zeman, and Andreas F. Prein
EGUsphere, https://doi.org/10.5194/egusphere-2026-1814, https://doi.org/10.5194/egusphere-2026-1814, 2026
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Despite steady improvements in forecasting skill, episodes of low forecast skill, called forecast busts, still persist. Using global ensemble simulations at different grid spacings, we show that coarse-grid simulations fail to resolve key mesoscale diabatic processes, and that errors upscale and propagate downstream, leading to large forecast errors. Fine grid spacing simulations better capture scale interactions in strongly diabatic flow, highlighting the potential of kilometer-scale models.
Tuule Müürsepp, Michael Sprenger, Heini Wernli, and Hanna Joos
Weather Clim. Dynam., 7, 547–565, https://doi.org/10.5194/wcd-7-547-2026, https://doi.org/10.5194/wcd-7-547-2026, 2026
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The tropopause region of the atmosphere is greatly impacted by the exchange of mass and constituents between the troposphere and the stratosphere. This study quantifies the role of radiation in troposphere-to-stratosphere transport using reanalysis data. We find that radiation contributes to this transport most of the time, albeit it might not be the dominant process. We provide a new insight into the complex interplay of processes that air parcels experience on their way to the stratosphere.
Jacopo Riboldi, Robin Noyelle, Ellina Agayar, Hanin Binder, Marc Federer, Katharina Hartmuth, Michael Sprenger, Iris Thurnherr, and Selvakumar Vishnupriya
Weather Clim. Dynam., 7, 65–87, https://doi.org/10.5194/wcd-7-65-2026, https://doi.org/10.5194/wcd-7-65-2026, 2026
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Storm Boris led to record-breaking precipitation over central Europe in September 2024. By incorporating event-specific meteorological information, this work introduces a methodology to strengthen our comprehension of how global warming affects similar hazards. Furthermore, it contextualizes how the answer to the question "How will Boris-like storms change in a warmer climate?" depends on explicit and implicit methodological choices, with the aim to inform future attribution research.
Ming Hon Franco Lee and Michael Sprenger
Weather Clim. Dynam., 6, 1583–1604, https://doi.org/10.5194/wcd-6-1583-2025, https://doi.org/10.5194/wcd-6-1583-2025, 2025
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Turbulence can occur in clear-air conditions at cruising altitude. From around 5000 clear-air turbulence events identified using aircraft measurements, nonlinear breaking of large-scale waves and rapidly ascending airstreams associated with cyclones are found concurrent with 40 % and 30 % of them respectively. The results further show that these weather systems may trigger turbulence by generating highly deformed flow or flow instability, improving our understanding of clear-air turbulence.
Emmanouil Flaounas, Stavros Dafis, Silvio Davolio, Davide Faranda, Christian Ferrarin, Katharina Hartmuth, Assaf Hochman, Aristeidis Koutroulis, Samira Khodayar, Mario Marcello Miglietta, Florian Pantillon, Platon Patlakas, Michael Sprenger, and Iris Thurnherr
Weather Clim. Dynam., 6, 1515–1538, https://doi.org/10.5194/wcd-6-1515-2025, https://doi.org/10.5194/wcd-6-1515-2025, 2025
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Storm Daniel (2023) is one of the most catastrophic storms ever documented in the Mediterranean. Our results highlight the different dynamics and therefore the different predictability skill of precipitation, its extremes and impacts that have been produced in Greece and Libya, the two most affected countries. Our approach concerns an analysis of the storm by articulating dynamics, weather prediction, hydrological and oceanographic implications, climate extremes, and attribution theory.
Selvakumar Vishnupriya, Michael Sprenger, Hanna Joos, and Heini Wernli
Weather Clim. Dynam., 6, 1195–1219, https://doi.org/10.5194/wcd-6-1195-2025, https://doi.org/10.5194/wcd-6-1195-2025, 2025
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Extratropical cyclones feature rapidly ascending airstreams known as warm conveyor belts, which could influence upper-level flow dynamics. This study classifies interactions between warm conveyor belt outflows and the jet stream into four types: no interactions, ridges, blocks, and tropospheric cutoffs. We use reanalysis data to demonstrate that the interaction type depends on the structure of the ambient flow than on the outflow, improving our understanding of extratropical flow variability.
Killian P. Brennan, Iris Thurnherr, Michael Sprenger, and Heini Wernli
Nat. Hazards Earth Syst. Sci., 25, 3693–3712, https://doi.org/10.5194/nhess-25-3693-2025, https://doi.org/10.5194/nhess-25-3693-2025, 2025
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Hailstorms can cause severe damage to homes, crops, and infrastructure. Using high-resolution climate simulations, we tracked thousands of hailstorms across Europe to study future changes. Large hail will become more frequent, hail-covered areas will expand, and instances of extreme hail combined with heavy rain will double. These shifts could increase risks for communities and businesses, highlighting the need for better preparedness and adaptation.
Killian P. Brennan, Michael Sprenger, André Walser, Marco Arpagaus, and Heini Wernli
Weather Clim. Dynam., 6, 645–668, https://doi.org/10.5194/wcd-6-645-2025, https://doi.org/10.5194/wcd-6-645-2025, 2025
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We studied severe hailstorms that occurred in Switzerland on 28 June 2021 using a weather prediction model to understand how they evolved. We found that the storms moved toward areas with more storm energy. Hailfall was quickly followed by heavy rain. Just before the storms died out, the air feeding them stopped coming from near the ground. We also observed a delay between different types of precipitation forming in the incoming air.
Nicolai Krieger, Heini Wernli, Michael Sprenger, and Christian Kühnlein
Weather Clim. Dynam., 6, 447–469, https://doi.org/10.5194/wcd-6-447-2025, https://doi.org/10.5194/wcd-6-447-2025, 2025
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This study investigates the Laseyer, a local windstorm in a narrow Swiss valley characterized by strong southeasterly winds during northwesterly ambient flow. Using large-eddy simulations (LESs) with 30 m grid spacing, this is the first study to reveal that the extreme gusts in the valley are caused by an amplifying interplay of two recirculation regions. Modifying terrain and ambient wind conditions affects the windstorm's intensity and highlights the importance of topographic details in LES.
Marc Federer, Lukas Papritz, Michael Sprenger, and Christian M. Grams
Weather Clim. Dynam., 6, 211–230, https://doi.org/10.5194/wcd-6-211-2025, https://doi.org/10.5194/wcd-6-211-2025, 2025
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Although extratropical cyclones in the North Atlantic are among the most impactful midlatitude weather systems, their intensification is not entirely understood. Here, we explore how individual cyclones convert available potential energy (APE) into kinetic energy and relate these conversions to the synoptic development of the cyclones. By combining potential vorticity thinking with a local APE framework, we offer a novel perspective on established concepts in dynamic meteorology.
Philip Rupp, Jonas Spaeth, Hilla Afargan-Gerstman, Dominik Büeler, Michael Sprenger, and Thomas Birner
Weather Clim. Dynam., 5, 1287–1298, https://doi.org/10.5194/wcd-5-1287-2024, https://doi.org/10.5194/wcd-5-1287-2024, 2024
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We quantify the occurrence of strong synoptic storms as contributing about 20 % to the uncertainty of subseasonal geopotential height forecasts over northern Europe. We further show that North Atlantic storms are less frequent, weaker and shifted southward following sudden stratospheric warming events, leading to a reduction in northern European forecast uncertainty.
Katharina Heitmann, Michael Sprenger, Hanin Binder, Heini Wernli, and Hanna Joos
Weather Clim. Dynam., 5, 537–557, https://doi.org/10.5194/wcd-5-537-2024, https://doi.org/10.5194/wcd-5-537-2024, 2024
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Warm conveyor belts (WCBs) are coherently ascending air streams that occur in extratropical cyclones where they form precipitation and often affect the large-scale flow. We quantified the key characteristics and impacts of WCBs and linked them to different phases in the cyclone life cycle and to different WCB branches. A climatology of these metrics revealed that WCBs are most intense during cyclone intensification and that the cyclonic and anticyclonic WCB branches show distinct differences.
Lukas Jansing, Lukas Papritz, and Michael Sprenger
Weather Clim. Dynam., 5, 463–489, https://doi.org/10.5194/wcd-5-463-2024, https://doi.org/10.5194/wcd-5-463-2024, 2024
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Using an innovative approach, the descent of foehn is diagnosed from a Lagrangian perspective based on 15 kilometer-scale simulations combined with online trajectories. The descent is confined to distinct hotspots in the immediate lee of local mountain peaks and chains. Two detailed case studies reveal a varying wave regime to be associated with the descent. Furthermore, additional controlling factors, such as the diurnal cycle, likewise influence the descent activity.
Hilla Afargan-Gerstman, Dominik Büeler, C. Ole Wulff, Michael Sprenger, and Daniela I. V. Domeisen
Weather Clim. Dynam., 5, 231–249, https://doi.org/10.5194/wcd-5-231-2024, https://doi.org/10.5194/wcd-5-231-2024, 2024
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The stratosphere is a layer of Earth's atmosphere found above the weather systems. Changes in the stratosphere can affect the winds and the storm tracks in the North Atlantic region for a relatively long time, lasting for several weeks and even months. We show that the stratosphere can be important for weather forecasts beyond 1 week, but more work is needed to improve the accuracy of these forecasts for 3–4 weeks.
Yonatan Givon, Or Hess, Emmanouil Flaounas, Jennifer Louise Catto, Michael Sprenger, and Shira Raveh-Rubin
Weather Clim. Dynam., 5, 133–162, https://doi.org/10.5194/wcd-5-133-2024, https://doi.org/10.5194/wcd-5-133-2024, 2024
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A novel classification of Mediterranean cyclones is presented, enabling a separation between storms driven by different atmospheric processes. The surface impact of each cyclone class differs greatly by precipitation, winds, and temperatures, providing an invaluable tool to study the climatology of different types of Mediterranean storms and enhancing the understanding of their predictability, on both weather and climate scales.
Stefania Gilardoni, Dominic Heslin-Rees, Mauro Mazzola, Vito Vitale, Michael Sprenger, and Radovan Krejci
Atmos. Chem. Phys., 23, 15589–15607, https://doi.org/10.5194/acp-23-15589-2023, https://doi.org/10.5194/acp-23-15589-2023, 2023
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Models still fail in reproducing black carbon (BC) temporal variability in the Arctic. Analysis of equivalent BC concentrations in the European Arctic shows that BC seasonal variability is modulated by the efficiency of removal by precipitation during transport towards high latitudes. Short-term variability is controlled by synoptic-scale circulation patterns. The advection of warm air from lower latitudes is an effective pollution transport pathway during summer.
Thomas Trickl, Martin Adelwart, Dina Khordakova, Ludwig Ries, Christian Rolf, Michael Sprenger, Wolfgang Steinbrecht, and Hannes Vogelmann
Atmos. Meas. Tech., 16, 5145–5165, https://doi.org/10.5194/amt-16-5145-2023, https://doi.org/10.5194/amt-16-5145-2023, 2023
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Tropospheric ozone have been measured for more than a century. Highly quantitative ozone measurements have been made at monitoring stations. However, deficits have been reported for vertical sounding systems. Here, we report a thorough intercomparison effort between a differential-absorption lidar system and two types of balloon-borne ozone sondes, also using ozone sensors at nearby mountain sites as references. The sondes agree very well with the lidar after offset corrections.
Melanie Lauer, Annette Rinke, Irina Gorodetskaya, Michael Sprenger, Mario Mech, and Susanne Crewell
Atmos. Chem. Phys., 23, 8705–8726, https://doi.org/10.5194/acp-23-8705-2023, https://doi.org/10.5194/acp-23-8705-2023, 2023
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We present a new method to analyse the influence of atmospheric rivers (ARs), cyclones, and fronts on the precipitation in the Arctic, based on two campaigns: ACLOUD (early summer 2017) and AFLUX (early spring 2019). There are differences between both campaign periods: in early summer, the precipitation is mostly related to ARs and fronts, especially when they are co-located, while in early spring, cyclones isolated from ARs and fronts contributed most to the precipitation.
Emmanouil Flaounas, Leonardo Aragão, Lisa Bernini, Stavros Dafis, Benjamin Doiteau, Helena Flocas, Suzanne L. Gray, Alexia Karwat, John Kouroutzoglou, Piero Lionello, Mario Marcello Miglietta, Florian Pantillon, Claudia Pasquero, Platon Patlakas, María Ángeles Picornell, Federico Porcù, Matthew D. K. Priestley, Marco Reale, Malcolm J. Roberts, Hadas Saaroni, Dor Sandler, Enrico Scoccimarro, Michael Sprenger, and Baruch Ziv
Weather Clim. Dynam., 4, 639–661, https://doi.org/10.5194/wcd-4-639-2023, https://doi.org/10.5194/wcd-4-639-2023, 2023
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Cyclone detection and tracking methods (CDTMs) have different approaches in defining and tracking cyclone centers. This leads to disagreements on extratropical cyclone climatologies. We present a new approach that combines tracks from individual CDTMs to produce new composite tracks. These new tracks are shown to correspond to physically meaningful systems with distinctive life stages.
Hanna Joos, Michael Sprenger, Hanin Binder, Urs Beyerle, and Heini Wernli
Weather Clim. Dynam., 4, 133–155, https://doi.org/10.5194/wcd-4-133-2023, https://doi.org/10.5194/wcd-4-133-2023, 2023
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Warm conveyor belts (WCBs) are strongly ascending, cloud- and precipitation-forming airstreams in extratropical cyclones. In this study we assess their representation in a climate simulation and their changes under global warming. They become moister, become more intense, and reach higher altitudes in a future climate, implying that they potentially have an increased impact on the mid-latitude flow.
Andreas Schäfler, Michael Sprenger, Heini Wernli, Andreas Fix, and Martin Wirth
Atmos. Chem. Phys., 23, 999–1018, https://doi.org/10.5194/acp-23-999-2023, https://doi.org/10.5194/acp-23-999-2023, 2023
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In this study, airborne lidar profile measurements of H2O and O3 across a midlatitude jet stream are combined with analyses in tracer–trace space and backward trajectories. We highlight that transport and mixing processes in the history of the observed air masses are governed by interacting tropospheric weather systems on synoptic timescales. We show that these weather systems play a key role in the high variability of the paired H2O and O3 distributions near the tropopause.
Hanin Binder, Hanna Joos, Michael Sprenger, and Heini Wernli
Weather Clim. Dynam., 4, 19–37, https://doi.org/10.5194/wcd-4-19-2023, https://doi.org/10.5194/wcd-4-19-2023, 2023
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Warm conveyor belts (WCBs) are the main cloud- and precipitation-producing airstreams in extratropical cyclones. The latent heat release that occurs during cloud formation often contributes to the intensification of the associated cyclone. Based on the Community Earth System Model Large Ensemble coupled climate simulations, we show that WCBs and associated latent heating will become stronger in a future climate and be even more important for explosive cyclone intensification than in the present.
Michael A. Barnes, Thando Ndarana, Michael Sprenger, and Willem A. Landman
Weather Clim. Dynam., 3, 1291–1309, https://doi.org/10.5194/wcd-3-1291-2022, https://doi.org/10.5194/wcd-3-1291-2022, 2022
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Stratospheric air can intrude into the troposphere and is associated with cyclonic development throughout the atmosphere. Through a highly idealized systematic approach, the effect that different intrusion characteristics have on surface cyclogenetic forcing is investigated. The proximity of stratospheric intrusions to the surface is shown to be the main factor in surface cyclogenetic forcing, whilst its width is an additional contributing factor.
Lukas Jansing, Lukas Papritz, Bruno Dürr, Daniel Gerstgrasser, and Michael Sprenger
Weather Clim. Dynam., 3, 1113–1138, https://doi.org/10.5194/wcd-3-1113-2022, https://doi.org/10.5194/wcd-3-1113-2022, 2022
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This study presents a 5-year climatology of three main foehn types and three deep-foehn subtypes. The main types differ in their large-scale and Alpine-scale weather conditions and the subtypes in terms of the amount and extent of precipitation on the Alpine south side. The different types of foehn are found to strongly affect the local meteorological conditions at Altdorf. The study concludes by setting the new classification into a historic context.
Jan Clemens, Felix Ploeger, Paul Konopka, Raphael Portmann, Michael Sprenger, and Heini Wernli
Atmos. Chem. Phys., 22, 3841–3860, https://doi.org/10.5194/acp-22-3841-2022, https://doi.org/10.5194/acp-22-3841-2022, 2022
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Highly polluted air flows from the surface to higher levels of the atmosphere during the Asian summer monsoon. At high levels, the air is trapped within eddies. Here, we study how air masses can leave the eddy within its cutoff, how they distribute, and how their chemical composition changes. We found evidence for transport from the eddy to higher latitudes over the North Pacific and even Alaska. During transport, trace gas concentrations within cutoffs changed gradually, showing steady mixing.
Jörg Wieder, Claudia Mignani, Mario Schär, Lucie Roth, Michael Sprenger, Jan Henneberger, Ulrike Lohmann, Cyril Brunner, and Zamin A. Kanji
Atmos. Chem. Phys., 22, 3111–3130, https://doi.org/10.5194/acp-22-3111-2022, https://doi.org/10.5194/acp-22-3111-2022, 2022
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We investigate the variation in ice-nucleating particles (INPs) relevant for primary ice formation in mixed-phased clouds over the Alps based on simultaneous in situ observations at a mountaintop and a nearby high valley (1060 m height difference). In most cases, advection from the surrounding lower regions was responsible for changes in INP concentration, causing a diurnal cycle at the mountaintop. Our study underlines the importance of the planetary boundary layer as an INP reserve.
Lukas Bösiger, Michael Sprenger, Maxi Boettcher, Hanna Joos, and Tobias Günther
Geosci. Model Dev., 15, 1079–1096, https://doi.org/10.5194/gmd-15-1079-2022, https://doi.org/10.5194/gmd-15-1079-2022, 2022
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Jet streams are coherent air flows that interact with atmospheric structures such as warm conveyor belts (WCBs) and the tropopause. Individually, these structures have a significant impact on the weather evolution. A first step towards a deeper understanding of the meteorological processes is to extract jet stream core lines, for which we develop a novel feature extraction algorithm. Based on the line geometry, we automatically detect and visualize potential interactions between WCBs and jets.
Philippe Besson, Luise J. Fischer, Sebastian Schemm, and Michael Sprenger
Weather Clim. Dynam., 2, 991–1009, https://doi.org/10.5194/wcd-2-991-2021, https://doi.org/10.5194/wcd-2-991-2021, 2021
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The strongest cyclone intensification is associated with a strong dry-dynamical forcing. Moreover, strong forcing and strong intensification correspond to a tendency for poleward cyclone propagation, which occurs in distinct regions in the Northern Hemisphere. There is a clear spatial pattern in the occurrence of certain forcing combinations. This implies a fundamental relationship between dry-dynamical processes and the intensification as well as the propagation of extratropical cyclones.
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Short summary
The Stratospheric Polar Vortex with its strong circumpolar jet is a dominant feature of the wintertime stratosphere. Evidence is presented of the characteristics of its distinctive sub-planetary scale features. The scale and dynamics of the features are linked to the break-up of an annular band of strong vorticity at the vortex's periphery, and moreover its aggregation into one or two vortices due to forcing from below can have ramifications for the occurrence of Sudden Stratospheric Warmings.
The Stratospheric Polar Vortex with its strong circumpolar jet is a dominant feature of the...
