Development of a Severe Storm Index Based on Environmental Conditions for Subtropical South America

Abstract

This study focuses on building a regional index to identify the occurrence of severe storms in Argentina based on large-scale environmental conditions, referred to as the Subtropical South American Severe Index (SSASE) The goal of thestudy is to assess the capability of the regional index in capturing the spatio-temporal distribution of severe storm occur-rence in the region. For building the regional index, a comprehensive database of severe storms covering the period from1991 to 2020 was gathered, based on multiple sources such as press reports and station reports. The regional index isbased on favorable environmental conditions capturing atmospheric instability, the 0 - 500 hPa wind shear and the mois-ture flux convergence. The addition of the latter, allows including one of the key ingredients for organized convection inthe region. Environmental conditions are taken from the ERA5 dataset. Results demonstrate that this approach provides arobust framework for generating a plausible climatology of the occurrence of severe events. The regional index allowedcharacterizing the annual and diurnal cycles of the occurrence of severe events and improved the representation of localfeatures in comparison with well known indices used worldwide, offering a more accurate depiction of severe stormactivity in the region.