Numerical investigation of the role of Saharan dust on the anomalous electrical structure of a thunderstorm over Corsica

Abstract

This study analyzes the role of dust particles on the formation of an anomalous charge structure in a thunderstorm observed on 14 October 2016 around Corsica. The cloud-resolving model Meso-NH with explicit aerosol-microphysics coupling is used to simulate realistically the interactions between the storm and the dust plume. This reference simulation shows no liquid water content in the convective region below −10 °C, which is conducive to only positive charging of the graupel according to traditional liquid water content temperature diagrams of the non-inductive charging mechanism. Differential hydrometeor fall speeds lead to a positive charge region below a negative charge region at the cloud scale, the so-called anomalous charge structure.

To disentangle between the radiative and microphysical role of dust particles on cloud structure, additional simulations are performed. First, using a climatological extinction of dust particles over Corsica, the microphysical structure of the storm is similar to the one of the reference simulation, excluding the radiative role of dust particles as a factor controling the charge structure in this case. Secondly, a low, constant and homogeneous ice nuclei particle concentration profile is imposed in the microphysics scheme. It enables the presence of supercooled water at temperatures below −20 °C, allowing the negative charging of the graupel at higher levels of the cloud, and potentially leading to a normal tripole. It highlights the role of desert dust as ice nuclei in the depletion of liquid water content in the mixed phase region of the cloud, which could lead to an anomalous charge structure.