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AS1.17

EDI
Meso-scale convection and disturbances in high-mountain environments

Mesoscale convective systems (MCSs) and meso-scale storms/disturbances are known to be important precipitation producing/triggering systems in high-mountain environments and on high-altitude plateaus. These meso-scale convective systems and disturbances can lead to severe weather locally and affect lower lying downstream regions.

The aim of this session is to gain an improved understanding of meso-scale systems and the associated processes leading to (extreme) precipitation in mountain regions and/or their downstream areas. We invite contributions on the dynamics of meso-scale storms/disturbances and meso-scale convective systems (including their formation and evolution) as well as smaller-scale convection in connection to atmospheric meso-scale features and how these factors explain spatio-temporal patterns of precipitation and precipitation dynamics. Contributions focussing on individual extreme events or giving climatological perspectives are welcome. Due to the nature of high-mountain environments it is difficult to directly observe their meso-scale atmospheric features and link these to the occurrence and spatio-temporal variability of precipitation. Therefore, contributions integrating remote sensing data, in-situ observations, and high-resolution models, especially those that explicitly resolve convections are particularly welcome.

This session is connected to the recently launched WRCP-CORDEX flagship pilot study “High resolution climate modelling with a focus on mesoscale convective systems and associated precipitation over the Third Pole region”.

Convener: Julia CurioECSECS | Co-conveners: Kalli Furtado, Jian Li, Julia KukuliesECSECS, Deliang Chen
Presentations
| Fri, 27 May, 11:05–11:50 (CEST)
 
Room 1.34

Fri, 27 May, 10:20–11:50

Chairpersons: Julia Curio, Kalli Furtado

11:05–11:08
Introduction

11:08–11:15
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EGU22-797
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ECS
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Highlight
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On-site presentation
Jérôme Kopp et al.

From June 18 to July 31, 2021, a series of exceptional hailstorms occurred over Switzerland, causing major damages to buildings, cars, and crop fields. The available estimates from the insurance companies suggest that these events will be among the most expensive of the last decades. At the same time the events provide a unique research opportunity as the hailstorms were well captured by various observing systems: a newly set-up network of automatic hail sensors that report the size and kinetic energy of individual hail stones with very high temporal and size resolution, the crowdsourcing function of the MeteoSwiss app, and two radar-based operational hail products. The recently established radar-based Swiss hail climatology shows that the events of 2021 were extreme with high return periods both in terms of the reported hail stone sizes and in their spatial extent. Using the data captured by those complementary hail-dedicated observing systems, we review the hail activity in Switzerland during the period of interest and investigate two particularly intense hail days: June 28 (HD1) and July 8 (HD2). On HD1, the storms originated in western Switzerland, moved along the northern flank of the Swiss Alps in a Southwest to Northeast motion, and one storm evolved in a mesoscale convective system. On HD2, the storms originated in Northern Italy and moved over Southern Switzerland (Ticino) in a South to North motion. We look at the synoptic-scale situation, mesoscale environment, and storm tracks of HD1 and HD2 in details and demonstrate their exceptional character with respect to the climatology. We touch upon the new research avenues opened by the automatic hail sensors measurements both individually, as they allow to capture the time evolution of the hail stones size distribution, and in combination with the crowdsourcing and radar data (cross-validation of the radar-based hail algorithms).

How to cite: Kopp, J., Schröer, K., Schwierz, C., Hering, A., Germann, U., and Martius, O.: The summer 2021 Switzerland hailstorms: major impacts and unique observational data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-797, https://doi.org/10.5194/egusphere-egu22-797, 2022.

11:15–11:22
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EGU22-6132
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ECS
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On-site presentation
Monika Feldmann et al.

Utilizing six years of radar-based thunderstorm data in the Swiss radar domain, we classify these as regular thunderstorms, hailstorms, severe hailstorms and mesocyclonic storms.

After identifying the overlaps between hailstorms and mesocyclones, their intensity lifecycles are investigated. This analysis allows the identification of predictors for intensification within severe storm lifecycles.

Subsequently we divide the radar domain into subregions ranging from the Po Valley, the Southern Prealps, main Alpine ridge, Northern Prealps, Swiss Plateau and Jura. This regional split separates storms in different terrain complexities. An investigation of the intensity distribution of storms in each region shows a clear intensity decrease over the main Alpine ridge, intermediate values over the moderately complex Prealpine regions and peaks for the flat Po Valley and Swiss Plateau.

These analyses investigate the influence of increasingly complex terrain on different types of severe convection from an observational perspective.

How to cite: Feldmann, M., Gabella, M., and Berne, A.: Hailstorms vs. supercells - a comparison of severe thunderstorms in the Alpine region, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6132, https://doi.org/10.5194/egusphere-egu22-6132, 2022.

11:22–11:29
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EGU22-2601
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ECS
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Virtual presentation
yin zhao
The Tibetan Plateau (TP) is known as Asian Water Tower and its atmospheric water cycle has been a lasting challenge to climate modeling community. Here, we compare two sets of the Met Office Unified Model simulations—one is a convection-parameterized version (large-scale model; LSM) and the other is a convection-permitting model (CPM) simulation. The added value of the CPM in terms of atmospheric water cycle process is analyzed, including external moisture transport, fraction of atmospheric water vapor converting to precipitation and the precipitation recycle ratio. Results show that the simulated TP precipitation and evaporation for the summer of 2009 is significantly improved in the CPM. First, the overestimation of atmospheric water cycle by LSM is improved in CPM due to a reasonable representation of the fraction of atmospheric water vapor converting to precipitation. The overestimation of precipitation recycle ratio also indicates the LSM generates excessive convection compared to the CPM and therefore has a larger wet bias over the TP. Second, a better simulation of local precipitation has feedback on the circulation. Compared with the LSM, the less moisture convergence in the CPM is dominated by the stronger outflow through the eastern edge of the TP rather than the weaker inflow, implying the upscale effects of the resolved moist convection on the moisture transport over the TP. Our results imply that the CPM is a useful tool in the reproduction of moisture transport and atmospheric water cycle process over the Asian Water Tower and other regions of the world with complex topography.

How to cite: zhao, Y.: Added Value of a Convection Permitting Model in Simulating Atmospheric Water Cycle Over the Asian Water Tower, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2601, https://doi.org/10.5194/egusphere-egu22-2601, 2022.

11:29–11:36
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EGU22-2644
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ECS
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Virtual presentation
Mengke Zhang et al.
Fine-scale characteristics of summer precipitation over Cang Mountain, a long and narrow mountain with a quasi-north–south orientation in Southwest China, are studied using station and radar data. Three kinds of rainfall processes are classifified according to the initial stations of regional rainfall events (RREs) by utilizing minute-scale rain gauge data. RREs initiating in the western part of Cang Mountain exhibit eastward evolution and tend to reach their maximum rainfall intensity on the mountaintop. The results indicate differences in the precipitation evolution characteristics between short-duration (1–3 h) and long-duration (at least 6 h) events. Short-duration events begin farther from the mountaintop and then propagate eastward, whereas long-duration events remain longer around the mountaintop. RREs that initiate from the eastern part of Cang Mountain display westward propagation and frequently reach their maximum rainfall intensity over the eastern slope of the mountain. Among them, short-duration events tend to propagate farther west of Cang Mountain at high speeds, but the westward evolution of long-duration events is mainly confifined to the eastern part of Cang Mountain. For mountaintop-originated RREs, precipitation quickly reaches its maximum intensity after it starts and then continues for a long time around the mountaintop during the period from late afternoon to early morning. These fifindings provide references for the fifine-scale prediction of precipitation evolution in small-scale mountainous areas.

How to cite: Zhang, M., Li, J., and Li, N.: Fine-Scale Characteristics of Summer Precipitation over Cang Mountain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2644, https://doi.org/10.5194/egusphere-egu22-2644, 2022.

11:36–11:43
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EGU22-6061
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ECS
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Virtual presentation
Gong Chen et al.

Synoptic analysis of a rainstorm occurred in Mianning, Sichuan, China started on June 26, 2020 is carried out in this study. During this event, the maximum observed precipitation occurred in Lingshansi station, reaching 181.9mm from 18:00 on June 26 to 02:00 on June 27, 2020(BJT) and resulting in a severe flood disaster. Through the analysis of various data (including FNL, ERA5, wind profile data), we found that a cold air flow gradually intrudes into the west of Sichuan Basin from north to south along the eastern edge of Qinghai-Tibet Plateau, during the process, a Southwest Vortex (A meso-ß vortex system often generated in Southwest China and prone to led heavy precipitation) gradually formed, and the precipitation in Mianning area occurred in the process of the formation of the Southwest Vortex. In order to determine whether the invasion of cold air into Sichuan Basin is the main factor triggering the generation of Southwest Vortex and rainstorm in this area with rough terrain, a series of numerical sensitivity experiments were carried out. The results show that the invasion of cold air plays an important role in the formation of the Southwest Vortex. The cold and warm air meet at the Anning river valley of Mianning and are forced to rise by terrain which leads to the strengthening of vertical circulation in the valley and the heavy rainstorm.

How to cite: Chen, G., Xu, J., and Zeng, B.: Analysis on the influence of cold air intrusion to the formation of a Southest Vortex and rainstorm in China, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6061, https://doi.org/10.5194/egusphere-egu22-6061, 2022.

11:43–11:50
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EGU22-11742
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ECS
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On-site presentation
Julia Curio et al.

Heavy summer precipitation events in the Sichuan basin, located at the eastern edge of the Tibetan Plateau (TP), can lead to disastrous flooding and landslides amplified by the complex terrain. Those events pose a threat to people’s lives and livelihood as well as infrastructure in this densely populated part of China.

Mesoscale convective systems (MCSs) were identified as the source of some heavy rainfall events in the downstream regions of the TP including the Sichuan basin. Some case studies argue that Tibetan Plateau vortices (TPV) play a crucial role in the development of MCSs and extreme rainfall events in the Sichuan basin.

MCSs are recognized as cloud clusters that produce heavy rainfall over large areas, while TPVs refer to frequently occurring meso-scale vortices that are initiated over the TP and mainly travel eastwards steered by the large-scale circulation. Around 20% of TPVs can move off the TP and affect the mainland of China, especially the regions close to the TP like the Sichuan basin and the upper reaches of the Yangtze and Yellow Rivers.

In this study, we identify the most extreme summer precipitation events in the Sichuan basin for the period 2000-2018 using daily accumulated rainfall observations from meteorological stations operated by the China Meteorological Administration (CMA). We analyse how many of those events are attributable to MCSs and if so whether there is a TPV in the vicinity affecting the MCS initiation and development. We make use of databases of MCSs and TPVs in the region of interest for which MCSs and TPVs have been identified using objective tracking algorithms.

Linking extreme precipitation events in this region to the occurrence and moving-off of TPVs may help to improve forecasts of extreme precipitation and subsequent flooding.

How to cite: Curio, J., Dugoul, A., Kukulies, J., and Chen, D.: Heavy summer precipitation events in the Sichuan basin and their connection to meso-scale convective systems and Tibetan Plateau vortices, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11742, https://doi.org/10.5194/egusphere-egu22-11742, 2022.