African convective system characteristics determined through tracking analysis

Abstract

African convective systems have been tracked over the period July to December 2004. A total of 82,140 Convective Systems (CSs) were identified, of which 52% were classified as thunderstorms (i.e., containing Cloud-to-Ground (CG) lightning flashes), and 48% as rain showers (i.e., without CG flashes). The properties of the CSs at different stages of life maturity are investigated in terms of CG lightning flashes, cloud area dynamics, precipitation and vertical structure. This study employs CG lightning measurements from a long-range lightning detection network (named ZEUS), 1/2-hourly satellite infrared observations, and Tropical Rainfall Measuring Mission-Precipitation Radar (TRMM-PR) rainfall and vertical reflectivity profile data. The area expansion rate of the storms at their initiation stage (i.e., growth) is found to be strongly linked to their life duration and size. The growth stage of T-storms exhibits high CG lightning density, which decreases rapidly to zero at dissipation stage. The convective rain type, obtained by TRMM-PR, is shown to be the dominant rain type during the growth and mature stages of the convective systems. Vertical structure was shown to depend on the maturity stage and type (thunderstorms vs. rain showers) of the storm. Particularly, deep vertical reflectivity gradients are noted in the growth stage of thunderstorms (associated with the strong mixing due to updraft and downdraft activities), while the dissipation stage is associated with weaker vertical structure. Results from this study exemplify the need of storm tracking information for improving the ice scattering–rainfall relationships used in overland microwave retrievals.