Normal versus anomalous thunderstorms, a comparison of electrical cells properties observed with the SAETTA LMA over the Corsican island
Authors: Houel Ronan , Defer Eric , Lambert Dominique , Prieur Serge , Pédeboy Stéphane , Gaussiat Nicolas , Radojevic Milka 
Published: March 2022

&lt;p&gt;&lt;span&gt;The north-western Mediterranean basin often experiences thunderstorms with heavy precipitation &lt;/span&gt;&lt;span&gt;and &lt;/span&gt;&lt;span&gt;intense lightning activity causing damages to this densely populated area. This study is conducted within the framework of the EXAEDRE (EXploiting new Atmospheric Electricity Data for Research and the Environment) project that aims 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. &lt;/span&gt;&lt;span&gt;These t&lt;/span&gt;&lt;span&gt;hunderstorms can exhibit d&lt;/span&gt;&lt;span&gt;istinct&lt;/span&gt;&lt;span&gt; vertical charge structure&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt; (&lt;/span&gt;&lt;span&gt;normal&lt;/span&gt;&lt;span&gt; and anomalous) that produce lightning &lt;/span&gt;&lt;span&gt;flashes&lt;/span&gt;&lt;span&gt; with different&lt;/span&gt; &lt;span&gt;properties&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;The goal of this study is to compare these &lt;/span&gt;&lt;span&gt;characteristics (CG production, flash polarity...&lt;/span&gt;&lt;span&gt;)&lt;/span&gt; &lt;span&gt;according&lt;/span&gt;&lt;span&gt; to both charge structure&lt;/span&gt;&lt;span&gt;s as measured&lt;/span&gt;&lt;span&gt; in Corsica. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;h&lt;/span&gt;&lt;span&gt;e&lt;/span&gt;&lt;span&gt; study &lt;/span&gt;&lt;span&gt;evaluates&lt;/span&gt;&lt;span&gt; the&lt;/span&gt; &lt;span&gt;properties&lt;/span&gt;&lt;span&gt; of &lt;/span&gt;&lt;span&gt;both types of &lt;/span&gt;&lt;span&gt;Corsican &lt;/span&gt;&lt;span&gt;storms at the &lt;/span&gt;&lt;span&gt;electrical cell s&lt;/span&gt;&lt;span&gt;cale&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;Hence&lt;/span&gt;&lt;span&gt;, 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 &lt;/span&gt;&lt;span&gt;LLS (Lightning Locating System)&lt;/span&gt;&lt;span&gt; METEORAGE are also &lt;/span&gt;&lt;span&gt;used&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;span&gt;We also add&lt;/span&gt;&lt;span&gt;&amp;#160;M&amp;#233;t&amp;#233;o France&lt;/span&gt;&lt;span&gt; weather radar &lt;/span&gt;&lt;span&gt;data&lt;/span&gt;&lt;span&gt; to &lt;/span&gt;&lt;span&gt;document&lt;/span&gt;&lt;span&gt; the cumulative rainfall associated to each &lt;/span&gt;&lt;span&gt;electrical &lt;/span&gt;&lt;span&gt;cell. &lt;/span&gt;&lt;span&gt;A clustering algorithm is &lt;/span&gt;&lt;span&gt;applied on the lightning data&lt;/span&gt;&lt;span&gt; to identify and track the cells. &lt;/span&gt;&lt;span&gt;Then we extract lightning and radar data for each cell&lt;/span&gt; &lt;span&gt;to &lt;/span&gt;&lt;span&gt;document&lt;/span&gt;&lt;span&gt; the evolution of several lightning-related &lt;/span&gt;&lt;span&gt;parameters &lt;/span&gt;&lt;span&gt;during th&lt;/span&gt;&lt;span&gt;eir&lt;/span&gt;&lt;span&gt; lifetime. We also &lt;/span&gt;&lt;span&gt;apply&lt;/span&gt; &lt;span&gt;a &lt;/span&gt;&lt;span&gt;recently published&lt;/span&gt; &lt;span&gt;method&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;to automatically &lt;/span&gt;&lt;span&gt;infer &lt;/span&gt;&lt;span&gt;the vertical structure of the electrical charge regions &lt;/span&gt;&lt;span&gt;within each cell. These algorithms allow us to create a database of &lt;/span&gt;&lt;span&gt;hundreds&lt;/span&gt;&lt;span&gt; of electrical cells in Corsica &lt;/span&gt;&lt;span&gt;for the period of study (June &amp;#8211; October 2018)&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;We first introduce the different &lt;/span&gt;&lt;span&gt;observations&lt;/span&gt;&lt;span&gt; and methodologies applied here. &lt;/span&gt;&lt;span&gt;Then we present the geographical and temporal distribution of the &lt;/span&gt;&lt;span&gt;normal and anomalous&lt;/span&gt;&lt;span&gt; cells over the study period. &lt;/span&gt;&lt;span&gt;Finally&lt;/span&gt; &lt;span&gt;we &lt;/span&gt;&lt;span&gt;compare the &lt;/span&gt;&lt;span&gt;electrical properties &lt;/span&gt;&lt;span&gt;associated to &lt;/span&gt;&lt;span&gt;these &lt;/span&gt;&lt;span&gt;different vertical charge structure configuration.&lt;/span&gt; &lt;span&gt;O&lt;/span&gt;&lt;span&gt;verall, anomalous cells represented around 15% of the cells population in Corsica over the study period. &lt;/span&gt;&lt;span&gt;A&lt;/span&gt;&lt;span&gt;nomalous&lt;/span&gt; &lt;span&gt;storms&lt;/span&gt; &lt;span&gt;produced &lt;/span&gt;&lt;span&gt;less&lt;/span&gt; &lt;span&gt;lightning jumps&lt;/span&gt;&lt;span&gt; per cell &lt;/span&gt;&lt;span&gt;but produced more CGs&lt;/span&gt; &lt;span&gt;relative to the total number of flashes per cell&lt;/span&gt;&lt;span&gt;. We also show that anomalous cells &lt;/span&gt;&lt;span&gt;tend to &lt;/span&gt;&lt;span&gt;form&lt;/span&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;horter flashes&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;The relationship between number of C&lt;/span&gt;&lt;span&gt;G&lt;/span&gt;&lt;span&gt;s and &lt;/span&gt;&lt;span&gt;cumulative&lt;/span&gt;&lt;span&gt; rain&lt;/span&gt;&lt;span&gt;fall&lt;/span&gt; &lt;span&gt;in &lt;/span&gt;&lt;span&gt;Corsica&lt;/span&gt; &lt;span&gt;for both charge structure &lt;/span&gt;&lt;span&gt;is linear and in accordance with &lt;/span&gt;&lt;span&gt;previous &lt;/span&gt;&lt;span&gt;results&lt;/span&gt;&lt;span&gt;. &lt;/span&gt;&lt;/p&gt;