Windstorms in Europe are responsible for more than half of the economic loss associated with natural disasters. In October 2018 a post-tropical cyclone, formerly Hurricane Leslie, made landfall in continental Portugal. This event was characterized by very intense winds, with a gust record-hitting value of 176 km/h registered near Figueira da Foz, a coastal city located in the center of the country. The main factors causing this event of extreme winds were likely a “cold-conveyor belt jet” or a “jet sting”, roughly 12 hours after losing its main tropical characteristics. Despite the strong impact associated with this windstorm there are still few studies modeling this kind of dynamics, and here we present a simulation and thorough analysis of the rare dynamics linked with this post-tropical cyclone affecting western Europe.

The WRF-ARW model, version 4.4.1, was used to numerically model Leslie as it transitioned from a hurricane to post-tropical cyclone. Three one-way nested domains were used with a large (5 km), medium (1 km), and lower (200m) resolution, with 68 hybrid levels (15 m - 20 hPa). The larger domain covers the Iberian Peninsula and a large portion of the Atlantic Ocean nearby, while the inner ones are focussed in the central and northern sectors of continental Portugal - the most affected areas. Initial and boundary conditions were retrieved from the GFS operational analysis at 0.25º spacing, in 6-hour intervals. Due to the difficulties modeling this cyclone, nudging was used in the outer domain to ensure that the cyclone would make landfall as close as possible to the real location.

Several state-of-the-art thermodynamics-based diagnostics were used to analyze in-depth the midlatitude cyclone dynamics observed in the recently transitioned cyclone Leslie. Midlatitude cyclone-related dynamics were identified in the simulation, leading to the extreme winds in the most impacted region. The set of final simulated data reveals a close resemblance to the real event, with parameterized wind gusts presenting a lower intensity around 140 km/h, but the largest values impacting approximately the same region of center Portugal. A Langragian approach was also used to study particle trajectories and evaluate the atmospheric circulation leading to the extreme winds showing vertical downdrafts up to 4 m/s. This study highlights the catastrophic potential a post-tropical cyclone such as Leslie has and, while at the end of their life-time with presumably less intensity, storms of this type should not be disregarded for warnings and need to be considered in general evaluations of midlatitude storm impacts.

Acknowledgements: This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020. M. M. Lima was supported through the PhD MIT Portugal MPP2030-FCT programme grant PRT/BD/154680/2023. L. C. Santos is supported by the EarthSystems Doctoral School, at University of Lisbon, supported by Portuguese Fundação para a Ciência e a Tecnologia (FCT) project UIDP/50019/2020-2023, University of Lisbon.

How to cite: Lima, M., C. Santos, L., M. Cardoso, R., M. M. Soares, P., and M. Trigo, R.: Langragian analysis of the extreme-windstorm dynamics associated to post-tropical cyclone Leslie landfall in Portugal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-599, https://doi.org/10.5194/egusphere-egu24-599, 2024.

Windstorms are among the most impacting natural hazards affecting Western and Central Europe. Information on the associated impacts and losses are essential for risk assessment and the development of adaptation and mitigation strategies. In this study, we compare reported and estimated windstorm losses from five datasets belonging to three categories: Indices combining meteorological and insurance aspects, natural hazard databases, and loss reports from insurance companies. We analyse the similarities and differences between the datasets in terms of reported events, the number of storms per dataset and the ranking of specific storm events for the period October 1999 to March 2022 across 21 European countries.

A total of 94 individual windstorms were documented. Only 11 of them were reported in all five datasets, while the large majority (roughly 60%) was solely recorded in single datasets. Results show that the total number of storms is different in the various datasets, although for the meteorological indices such number is fixed a priori. Additionally, the datasets often disagree on the storm frequency per winter season. Moreover, the ranking of storms based on reported/estimated losses varies in the datasets. However, these differences are reduced when the ranking is calculated relative to storm events that are common in the various datasets. The results generally hold for losses aggregated at European and at country level.

Overall, the datasets provide different views on windstorm impacts. Thus, to avoid misleading conclusions, we use no dataset as “ground truth” but treat all of them as equal. We suggest that these different views can be used to test which features are relevant for calibrating windstorm models in specific regions. Furthermore, it could enable users to assign an uncertainty range to windstorm losses. We conclude that a combination of different datasets is crucial to obtain a representative picture of windstorm associated impacts.

How to cite: Moemken, J., Messori, G., and Pinto, J. G.: Windstorm losses in Europe - What to gain from damage datasets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1418, https://doi.org/10.5194/egusphere-egu24-1418, 2024.

Extreme extra-tropical cyclones and related windstorms are the most dangerous and costly meteorological hazards in Europe. The latest state-of-the-art seasonal forecast suites show now usable forecast skill for basic parameters like mean temperature or precipitation for mid-latitude Europe on lead times of up to 4 months (Nov-Feb). One avenue for skilful prediction of extremes is the now-proven forecast skill for large-scale climate modes, as these directly influence extreme windstorms. Improved ability to simulate successfully the relevant large-scale climate patterns like e.g., the North-Atlantic Oscillation, the East-Atlantic pattern, and/or the Scandinavian pattern opens up a prominent route to progress the forecast skill for extreme storms.

Nevertheless, recent publications have shown that even in the current model suites, the existing skill for forecasting the frequency or intensity of windstorm tail events, is not fully explained by those dominant large-scale variability patterns. Furthermore, studies revealed a potential connectivity of storm count predictions to stratospheric sudden warming events and also highlighting the influence of atmosphere-ocean coupling. Recent developments in the forecast skill of the upper-ocean heat content and the role of re-emerging temperature anomalies for the European winter climate allow to explore another pathway with potentially predictive power, the role of ocean-atmosphere interaction. Ocean-atmosphere interaction caused e.g., by the NAO have been increasingly recognised but have not been systematically linked to the ability to predict extreme severe windstorms on a seasonal time scale. In this presentation, we will present preliminary results of the role of ocean on the predictability of European windstorms.

How to cite: Ng, K. S. and Leckebusch, G. C.: An Investigation into the Role of the Ocean for Seasonal Predictability of European Windstorms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1553, https://doi.org/10.5194/egusphere-egu24-1553, 2024.

Severe European winter windstorms are one of the most damaging natural hazards and thus a major threat to societies. Clustered European winter windstorms, storms that occur in quick succession over a specific period of time over a fixed location, can result in amplified structural and environmental damage and accumulated losses. Yet, variability of storm clustering on intra-seasonal timescales has not been fully investigated. We analyse winters (DJF) for the period 1981-2016 from ERA5 reanalysis, where tracks and storm impact footprints are identified through the impact-oriented wind-based tracking algorithm WiTRACK.  

We quantify the magnitude of clustering using the widely employed dispersion statistic as used in Mailier et al. (2006). The spatial distribution of clustering on 45- and 30-day timescales as well as the time development of clustering on even shorter 30-, 20-, 15- and 11-days reference periods are investigated. Thus, in a seamless approach from seasonal to synoptic clustering. Results from both windstorm clustering of tracks and the storm footprints will be presented. Preliminary findings suggest an increase in clustering occurrence in the later half of the winter season on 45- and 30-day timescales.  On shorter timescales (<30 days), depending on location, distinct periods of increased clustering e.g., in the middle and the end of the season can be identified.

How to cite: Feltz, S., Leckebusch, G. C., Ng, K. S., and Kruschke, T.: Intra-seasonal variability of temporal clustering of European winter windstorms, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1736, https://doi.org/10.5194/egusphere-egu24-1736, 2024.

Windstorms are one of the most destructive natural disasters in Europe, causing considerable human and economic impacts, ranging from fatalities and injuries to damage to agriculture, infrastructures, and properties. The European Commission’s Joint Research Centre (JRC) estimates annual losses of 5 €-billion for the European Union and United Kingdom (Spinoni et al., 2020). While in these areas there is not high confidence on the projected changes in windstorm intensity and frequency due to climate change (Ranasinghe et al., 2021), damages resulting from windstorms will most likely increase in the future due to the appreciation of asset values (Spinoni et al., 2020).

Although Italy is one of the most affected European countries, with annual absolute losses estimated above 0.5 €-billion (Spinoni et al., 2020), windstorm is still considered to be a secondary peril. However, severe windstorm events in the last few years (e.g., Storm Vaia in October 2018) have raised an increasing interest of the Italian insurance industry in understanding and modelling this peril.

In this context, we aim at developing a catastrophe model that quantifies the financial impacts of windstorms on the insurance market in Italy. To this aim, here we perform the calibration of a stochastic windstorm event set for the hazard component of the model. Uncalibrated footprints are obtained from simulation outputs of global and regional numerical models. Then, historical event footprints are extracted from open-access reanalysis datasets (e.g., ERA5, CERRA) and used to correct the climatology of the stochastic set and to adjust the wind-speeds of its individual events. This analysis is expected to be preparatory for the development of a comprehensive catastrophe model that combines wind hazard with exposure and vulnerability to assess windstorm-related financial losses in Italy.

References:

Ranasinghe, R., et al., 2021: Climate Change Information for Regional Impact and for Risk Assessment. In Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Masson-Delmotte, V., et al., (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1767–1926, doi: 10.1017/9781009157896.014.

Spinoni, J., et al., 2020: Global warming and windstorm impacts in the EU, EUR 29960 EN, Publications Office of the European Union, Luxembourg, 2020, ISBN 978-92-76-12955-4, doi:10.2760/039014. JRC118595.

How to cite: Aiazzi, L., Persiano, S., Bottazzi, M., Gallotti, G., Petruccelli, A., Ait-Chaalal, F., and Leoncini, G.: A catastrophe model for Windstorm in Italy: developing a stochastic windstorm event set adjusted with open-access reanalysis datasets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6370, https://doi.org/10.5194/egusphere-egu24-6370, 2024.

Extratropical cyclones play a dominant role in the Mediterranean. They are important for local water supplies, but they can also cause severe damage due to heavy winds, extreme precipitation and coastal floods. Over the last decades, a decrease in the number of extratropical cyclones in the Mediterranean has been observed. Climate models suggest that this decreasing trend will continue in the future under global warming, leading to fewer storms and dryer conditions over the region compared to the present. However, it is much less clear how extreme cyclones in the Mediterranean will respond to climate change. Our previous study, based on a simulation from the Community Earth System Model (CESM) covering the last 3500 years, indicates that extreme cyclones show a distinct centennial variability in frequency, cyclone-related precipitation and wind speed. In addition, we found a weak relation between atmospheric circulation modes and varying cyclone characteristics across different regions in the Mediterranean. However, the coarse horizontal resolution of CESM (2.0°×2.5°) is not very well suited to resolve the mesoscale cyclones that often occur in the Mediterranean. For this study, we downscaled the CESM simulation for the period 1821–2100 (RCP8.5 scenario from 2005 onwards) to a horizontal grid resolution of 20 km using the Weather Research and Forecasting (WRF) model. The WRF simulation can resolve the cyclone characteristics in the Mediterranean more accurately than CESM. Additionally, the WRF simulation is able to reproduce the complexity of cyclone-related wind speed and precipitation in a much more detailed way. Preliminary results show a strong decrease in cyclone frequency as a result of global warming. However, this trend is much less clear for extreme cyclones with respect to wind speed and precipitation. Using the long downscaled WRF simulation, we intend to identify characteristics in CESM that lead to extreme wind and precipitation in the downscaled simulation. Additionally, we will investigate the most extreme wind and precipitation events in the Mediterranean to understand what processes are better captured at smaller scales than in the global model.

How to cite: Doensen, O., Messmer, M., Kim, W. M., and Raible, C.: Past and future Mediterranean cyclone characteristics using a regional climate model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8101, https://doi.org/10.5194/egusphere-egu24-8101, 2024.

This study explores whether and why a warmer climate induces alterations in climatological statistics and the underlying physical features of lee cyclogenesis in the Euro-Mediterranean region.

The investigation focuses on a specific cyclogenesis type, wherein orography (the Alps), influences the spatial structure and growth rate of the cyclone.

This regional scale phenomenon is inspected within the framework of a general weakening and poleward shift of the mid-latitude jet. This large-scale signal, despite being evident in zonal-averaged results from the majority of climate models, remains subject to considerable uncertainty when specific regions and seasons are considered. This uncertainty stems from the intricate interplay and delicate equilibrium among numerous competing mechanisms.

The analysis focuses on historical and future trends during the cold semesters across the Euro-Mediterranean region. The historical period is examined using ERA5 reanalysis spanning from 1940 to the present, supplemented by a higher-resolution regional reanalysis product (COSMO-REA6) at approximately 6 km resolution, covering the period 1995-2019 over the Euro-CORDEX (EUR11) domain. State-of-the-art high-resolution climate models are employed to assess historical reproducibility and future trends through an ensemble of global climate models from the HighResMIP initiative.

Methodologically, two distinct approaches are pursued. Firstly, changes in statistical properties of lee cyclogenesis are examined, along with composites of precipitation and wind extremes footprint, utilizing two tracking algorithms: TempestExtremes (Ullrich et al., 2021) and TRACK (Hodges, 1994). These algorithms differ in their identification/tracking variables, i.e., mean sea level pressure and 850hPa relative vorticity, respectively. Secondly, an empirical orthogonal function (EOF) analysis is employed to evaluate whether dominant spatial patterns of relevant variables (e.g., mean sea level pressure and 500hPa geopotential height) associated with cyclogenesis undergo significant changes across different time segments.

This investigation is conducted as a spin-off of the Copernicus-ECMWF-funded contract C3S2_413 - Enhanced Operational Windstorm Service. The findings aim to enhance our understanding of the complex dynamics of Euro-Mediterranean lee cyclogenesis in the context of a changing climate, providing further insights for climate science and operational windstorm services.

How to cite: Sangelantoni, L., Tibaldi, S., Cavicchia, L., Peano, D., and Scoccimarro, E.: Climate change signature on Euro-Mediterranean lee cyclogenesis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11704, https://doi.org/10.5194/egusphere-egu24-11704, 2024.

During the extended winter period from December 2017 to April 2021, the Iberian Peninsula (IP) was impacted by several high-impact storms characterized by intense precipitation and/or strong winds. This study provides a detailed assessment of the events, including synoptic conditions, large-scale dynamics associated with the storms, and a climatological analysis aimed at improving public understanding and preventing natural disasters. The analysis of the cyclones’ variability indicates that their maximum intensity varies between 955 hPa and 985 hPa, with a duration of two to four days, and the most frequent occurrence (eight events) was in January. At the peak of maximum intensity, the composite anomaly patterns showed lower mean sea level pressure (MSLP) values (−21.6 hPa), higher water vapor values (327.6 kg m⁻¹s⁻¹), and wind speed at 250 hPa exceeding 29.6 m s⁻¹ the mean values. Additionally, there were high anomaly values of equivalent potential temperature (θe) of 19.1 °C at 850 hPa, sea surface temperature (SST) anomaly values of −1 °C, and negative anomaly values of surface latent heat flux (Q_E) (−150 W m⁻²) close to the IP. During the days impacted by the storms, the recorded values surpassed the 98th percentile in a significant percentage of days for daily accumulated precipitation (34%), instantaneous wind gusts (46%), wind speed at 10 m (47%), and concurrent events of wind/instantaneous wind gusts and precipitation (26% and 29%, respectively). These findings allow us to describe their meteorological consequences on the IP, particularly the effects resulting from intense precipitation such as floods, and strong winds associated with various destructive impacts. Finally, clear, real-time, and predictive information about weather systems and their impacts is crucial for the public to understand and enable effective responses to mitigate these natural hazards damage.

Keywords: extreme events; extratropical cyclones; explosive development cyclones; winter storms; Iberian Peninsula.

Acknowledgments

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC)–UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020), UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and LA/P/0068/2020 (https://doi.org/10.54499/LA/P/0068/2020), and project WEx-Atlantic (PTDC/CTAMET/29233/2017, LISBOA-01-0145-FEDER-029233, NORTE-01-0145-FEDER-029233). FCT is also providing for Ana Gonçalves doctoral grant (2021.04927.BD). The EPhysLab group was also funded by Xunta de Galicia, Consellería de Cultura, Educación e Universidade, under project ED431C 2021/44 “Programa de Consolidación e Estructuración de Unidades de Investigación Competitivas.

 References

Gonçalves, A.C.R.; Nieto, R.; Liberato, M.L.R. Synoptic and Dynamical Characteristics of High-Impact Storms Affecting the Iberian Peninsula during the 2018–2021 Extended Winters. Atmosphere 2023, 14, 1353. https://doi.org/10.3390/atmos14091353

How to cite: C. R. Gonçalves, A., Nieto, R., and L. R. Liberato, M.: High-impact storms during the extended winters of 2018–2021 in the Iberian Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16593, https://doi.org/10.5194/egusphere-egu24-16593, 2024.

How to cite: Cavicchia, L., Scoccimarro, E., and Gualdi, S.: Towards AI-enhanced prediction of Mediterranean cyclones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14305, https://doi.org/10.5194/egusphere-egu24-14305, 2024.

Cut-off Lows (COLs) are mid-latitude storms that are detached from the main westerly flow. They tend to propagate slower than other mid-latitude storms and are often harbingers of heavy and persistent rainfall. COLs have long been subject to thorough studies that have examined the physical structure and climatology across both hemispheres, however, their assessment in models is relatively low. In fact, there is no study on future changes in COLs in models. In this study, we analyze the cut-off lows in the northern hemisphere in the historic and future time slices in the CMIP6 dataset to study the frequency, duration, and intensity of the cut-off lows alongside the changes in velocity. Results show that the COL season, which is currently mostly limited to summer, extends into spring over Europe, North America, and Asia. This rise in activity in spring is more pronounced for COLs that are long-lasting and also have higher intensity maxima, i.e., the most impactful ones. Moreover, COL propagation velocity for persistent systems is due to slow down over North America in the summer. Slow-moving COLs are known to cause heavy localized rainfall. Through this study, we fill the information gap on the first insights of projected future changes in COLs by using TRACK to detect and trace COLs in the SSP5-8.5 projections of the CMIP6 ensemble.

How to cite: Mishra, A. N., Maraun, D., Schiemann, R., Hodges, K., and Zappa, G.: Climate change's influence on Cut-off Lows in the future, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19896, https://doi.org/10.5194/egusphere-egu24-19896, 2024.

The Indian Himalayan region receives an enormous amount of precipitation due to synoptic weather systems known as Western Disturbances (WDs). WDs are east-ward propagating systems embedded in the Subtropical Westerly Jetstream (SWJ). The main objective of this study is to investigate the change in magnitude and dynamics of WDs precipitation over the western Himalayan region. In this study, different observational datasets (IMD, AHRODITE, GPCP, GPCC, and ERA5) were selected to compare and assess the magnitude of WDs precipitation for the period 1987–2020 during the winters (DJF: December, January, and February). Further, to examine the structure of WDs precipitation at the pressure level of 200hPa, ERA5 Reanalysis datasets having a similar resolution of 25 km with the gridded dataset of the Indian Meteorological Department (IMD) are used for the analysis. WDs moisture sources from the Arabian Sea are assessed at 23 pressure levels (1000–200 hPa) for further understanding of WDs dynamics. Our study shows the daily shifting of WDs precipitation towards February during the winters and an intriguing decrease in daily WDs precipitation in recent years. During the study, we found that WDs precipitation contributed a significant amount of precipitation (~80%) over the Western Himalayan region of the Indian subcontinent. Using Theil-Sen method, trend analysis was performed, showing a decreased trend of WDs precipitation in recent years The present findings indicate that WDs have changed their precipitation characteristics and dynamics due to climate change. The number of active WDs days is decreasing. Our results show there is enough moisture present over the Bay of Bengal region other than WDs which helps in sustaining and replenishing glaciers over the Indian Himalayan region.

How to cite: Pooja, P. and Dimri, A. P.: Shifting of Western Disturbances winter precipitation over Western Himalayas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1974, https://doi.org/10.5194/egusphere-egu24-1974, 2024.