Observational and modeled-based study of inverted polarity thunderstorms documented in Corsica during the EXAEDRE project

Abstract:

The north-western Mediterranean basin often experiences thunderstorms with heavy precipitation, strong wind and lightning activity. One of the objectives of the EXAEDRE (EXploiting new Atmospheric Electricity Data for Research and the Environment) project is to better monitor the thunderstorms in this area through a better understanding of the physical processes that drive the dynamics, the microphysics and the electrical activity of the convective systems. Electrical characteristics such as flash rate, charge layers or flash polarity are good proxies for thunderstorms monitoring and good evidences of the storm severity.

As a first step we study an inverted polarity thunderstorm that occurred over Corsica on 21 July 2018. For that, observations of the LMA (Lightning Mapping Array) SAETTA network, deployed in Corsica, are used to document in 3D the total lightning activity. Complementary 2D lightning observations recorded by the French national lightning detection network METEORAGE are also investigated. A clustering algorithm is used to identify and track the electrical cells to study the evolution of several lightning-related characteristics during the lifetime of each electrical cell. We also developed a method based on lightning leader velocity to automatically characterize the vertical structure of the electrical charge regions.

We first introduce the different observations and methodologies applied here. Then the main electrical properties of the inverted polarity 21 July 2018 thunderstorm (e.g. flash duration, vertical flash extension, charge layer, flash type and polarity) as well as their temporal evolution are presented. This storm produced few cloud-to-ground lightning strikes and they were predominantly of negative polarity. Those electrical properties are then compared to the ones measured during the regular polarity 09 July 2018 thunderstorm. Finally this observational-based study is coupled with a series of numerical simulations performed with the cloud resolving model MesoNH and its electrification and lightning schemes.