Convective cloud activity and associated lightning during the five large-scale Darwin wet season regimes

 

Author

Vickal Vikash Kumar — Monash University

Category

Cloud Properties

Description

A two-wet-season data set from the Darwin C-band polarimetric radar and the World Wide Lightning Location Network is analysed to investigate the diurnal variability of convective cloud-top heights and associated lightning. The analysis is performed separately for five identified large-scale Darwin wet season regimes and for the three underlying surfaces: oceanic, coastal, and continental. The convective cloud occurrences are derived using two methods: the Steiner algorithm and the Thunderstorm Identification, Tracking, Analysis and Nowcasting (TITAN) system. We find that during their early growth phase, convective clouds are shallow with a peak occurrence height of approximately 9 km (and volume less than 30 km3), and these, within few hours, grow into deeper convective towers with a peak occurrence height of approximately 14 km. For the coastal and continental regions, a majority of convective clouds develop in the afternoon, initiated by the sea breeze convergence, except during the active monsoon regime. In the active monsoon regime, convective cloud activity exhibits oceanic characteristics with a relatively low (approximately 11 km) peak occurrence height, smaller than average convective cloud volumes (36 km3) and electrically least active convective cells. The “shallow westerly” regime is found to be electrically most active and produces the highest convective towers; this is believed to be caused by a higher amount of low-level wind convergence. The main conclusions of our study are that: (a) convective cell size depends on the large-scale atmospheric regime, the nature of the underlying surface, and the local time; (b) the cell kinematics (speed, lifetime, and direction of propagation) are mainly dependent on the large-scale atmospheric regime, and (c) the cell initiation mechanisms depend mainly on local time and the nature of underlying surface.