Object-based analysis of simulated thunderstorms in Switzerland: application and validation of automated thunderstorm tracking with simulation data

Timothy H Raupach,Yannick Barton,Alessandro Hering,Luca Nisi,Olivia Martius,Andrey Martynov

doi:10.5194/gmd-14-6495-2021

Abstract

Abstract. We present a feasibility study for an object-based method to characterise thunderstorm properties in simulation data from convection-permitting weather models. An existing thunderstorm tracker, the Thunderstorm Identification, Tracking, Analysis and Nowcasting (TITAN) algorithm, was applied to thunderstorms simulated by the Advanced Research Weather Research and Forecasting (AR-WRF) weather model at convection-permitting resolution for a domain centred on Switzerland. Three WRF microphysics parameterisations were tested. The results are compared to independent radar-based observations of thunderstorms derived using the MeteoSwiss Thunderstorms Radar Tracking (TRT) algorithm. TRT was specifically designed to track thunderstorms over the complex Alpine topography of Switzerland. The object-based approach produces statistics on the simulated thunderstorms that can be compared to object-based observation data. The results indicate that the simulations underestimated the occurrence of severe and very large hail compared to the observations. Other properties, including the number of storm cells per day, geographical storm hotspots, thunderstorm diurnal cycles, and storm movement directions and velocities, provide a reasonable match to the observations, which shows the feasibility of the technique for characterisation of simulated thunderstorms over complex terrain.

Highlights

Convection-permitting simulations will play a critical role in reducing the existing high uncertainty around the responses of thunderstorms (e.g. Diffenbaugh et al, 2013; Collins et al, 2013; Hartmann et al, 2013; Allen, 2018) and hailstorms (e.g. Martius et al, 2018; Allen, 2018; Raupach et al, 2021b) to climate change
Storm properties found using TITAN with WRF simulation output are compared to those found using Thunderstorms Radar Tracking (TRT) with radar data to test whether TITAN applied to WRF simulations can produce representative statistics on thunderstorms in Switzerland
TITAN was run over the WRF simulation outputs, and TRT results were subset to the same period of time

Summary

Introduction

Convection-permitting simulations will play a critical role in reducing the existing high uncertainty around the responses of thunderstorms (e.g. Diffenbaugh et al, 2013; Collins et al, 2013; Hartmann et al, 2013; Allen, 2018) and hailstorms (e.g. Martius et al, 2018; Allen, 2018; Raupach et al, 2021b) to climate change. Martius et al, 2018; Allen, 2018; Raupach et al, 2021b) to climate change. Such models have sufficiently high resolution to explicitly resolve individual storm structures without parameterised convection High-resolution simulations can be difficult to compare either to one another or to observations, since mismatches in timing or location of weather features can occur even when the overall statistical properties of the weather phenomena are in agreement, leading to point-to-point comparison results that do not properly show model performance Object-based approaches have been used to study properties of mesoscale convective systems Object-based approaches have been used to study properties of mesoscale convective systems (e.g. Feng et al, 2019; Song et al, 2019) and evalu-

Objectives

Methods

Results

Conclusion