Unique observational data from an automatic hail sensors network in Switzerland

We present an investigation of the first observations from the Swiss Hail Network Project, a network of 80 fully automatic hail sensors (Kopp et al., 2022) installed between 2018 and 2020 in the three most hail-prone regions of Switzerland: the Jura, the Napf and Ticino (NCCS 2021). Those sensors provide new hail ground-based information, not only about each hailstone size (estimated by an indirect measures of its kinetic energy), but also about the precise timing of hailstone individual impact (Löffler-Mang et al., 2011), allowing to obtain a time-resolved hail size distribution (HSD). More specifically, we investigate the point (local) duration of hailfalls, the event hit rate (impacts per second) and time-resolved HSD. We also present and discuss the potential sources of uncertainty specific to the hail sensor, such as the dead time (minimum time between two consecutive observations). We then compare our observations to measurements from an hailpads network in northeastern Italy (Manzato et al., 2022). While our sample is still limited (around 10’000 hailstone impacts registered during 4 warm seasons) with respect to the hailpads records (29 warm seasons), we found that the HSD obtained with both measurements’ devices are very close to each other. Finally, we discuss the further combination of the sensor data with radar hail products (Kopp et al., 2022), the exceptionally high density of crowdsourced hail reports collected in Switzerland (Kopp et al., 2022) and the recent drone measurements of hail (Martin Lainer et al., abstract ECSS2023-5), which could pave the way to new and exciting research avenues on hail understanding and forecasting. Kopp, J., Schröer, K., Schwierz, C., Hering, A., Germann, U. and Martius, O. (2022), The summer 2021 Switzerland hailstorms: weather situation, major impacts and unique observational data. Weather. https://doi.org/10.1002/wea.4306 Löffler-Mang, Martin, Dominik Schön, and Markus Landry. 2011. « Characteristics of a New Automatic Hail Recorder ». Atmospheric Research 100 (4): 439‑46. https://doi.org/10.1016/j.atmosres.2010.10.026. Manzato, Agostino, Andrea Cicogna, Massimo Centore, Paolo Battistutta, and Mauro Trevisan. 2022. « Hailstone Characteristics in NE Italy from 29 Years of Hailpad Data ». Journal of Applied Meteorology and Climatology, août. https://doi.org/10.1175/JAMC-D-21-0251.1. NCCS (2021) National Centre for Climate Services : Hail climatology Switzerland. https://www.nccs.admin.ch/nccs/en/home/the-nccs/priority-themes/hail-climate-switzerland.html, accessed 26 December 2022