Preprints
https://doi.org/10.5194/egusphere-2024-2148
https://doi.org/10.5194/egusphere-2024-2148
19 Jul 2024
 | 19 Jul 2024

An object-based and Lagrangian view on an intense hailstorm day in Switzerland as represented in COSMO-1E ensemble hindcast simulations

Killian P. Brennan, Michael Sprenger, André Walser, Marco Arpagaus, and Heini Wernli

Abstract. On 28 June 2021, Switzerland experienced the passage of several formidable hailstorms, navigating its complex terrain. They unleashed severe hailstones measuring up to 9 cm in diameter. We present a comprehensive case study to unravel the complex processes involved in the genesis, intensification, and dissipation of this impactful weather event. To this end, we investigate ensemble hindcast simulations using the COSMO-1E numerical weather prediction model that includes the HAILCAST hail growth parameterization. A tracking algorithm is introduced that facilitates the object-based analysis of the simulated hailstorms, addressing the inherent challenges of tracking hailstorms within numerical simulation outputs. By scrutinizing the storm's evolution across various phases, particularly during intensification, the study conducts a storm-relative analysis of 100 hailstorms simulated on this day by the 11-member ensemble with lifetimes of >2.5 h. Furthermore, the investigation utilizes Lagrangian air parcel trajectories initiated along the hail track to analyze the inflow of air sustaining the storm updraft. This exploration provides fresh insights into the low-level flow patterns and moisture sources contributing to the storm's vigor, and it reveals the importance of topography for the various stages of the storms. The most important findings from this detailed hailstorm investigation are (i) COSMO-1E with HAILCAST produces realistic storm tracks and lifespans that are in good agreement with radar observations, (ii) intricate storm structures are resolved in the simulations and reveal hail fall followed by precipitation, and (iii) Lagrangian trajectories show that inflowing air can be drawn across the main Alpine crest and experiences rain before reaching saturation conditions in the storm.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Killian P. Brennan, Michael Sprenger, André Walser, Marco Arpagaus, and Heini Wernli

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-2148', Anonymous Referee #1, 04 Sep 2024
  • RC2: 'Comment on egusphere-2024-2148', Anonymous Referee #2, 19 Sep 2024
  • EC1: 'Comment on egusphere-2024-2148', Johannes Dahl, 20 Sep 2024
  • AC1: 'Final author comments egusphere-2024-2148', Killian Brennan, 25 Oct 2024
    • EC2: 'Reply on AC1', Johannes Dahl, 28 Oct 2024
Killian P. Brennan, Michael Sprenger, André Walser, Marco Arpagaus, and Heini Wernli
Killian P. Brennan, Michael Sprenger, André Walser, Marco Arpagaus, and Heini Wernli

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Short summary
Our study looked at the intense hailstorms in Switzerland on June 28, 2021. We used detailed computer simulations to understand how these storms formed, grew stronger, and eventually faded away. By tracking storm features and studying the airflows and weather conditions around them, we found that our model accurately predicted storm paths and lifespans. The storms showed complex patterns of hail and rain. This research can help improve the forecasting and handling of severe weather events.