The Relationship between Precipitation and Lightning in Tropical Island Convection: A C-Band Polarimetric Radar Study

Abstract

One of the primary scientific objectives of the Maritime Continent Thunderstorm Experiment was to study cloud electrification processes in tropical island convection, in particular, the coupling between ice phase precipitation and lightning production. To accomplish this goal, a C-band polarimetric radar was deployed in the Tropics (11.68S, 130.88E) for the first time, accompanied by a suite of lightning measurements. Using observations of the propagation-corrected horizontal reflectivity and differential reflectivity, along with specific differential phase, rain and ice masses were estimated during the entire life cycle of an electrically active tropical convective complex (known locally as Hector) over the Tiwi Islands on 28 November 1995. Hector’s precipitation structure as inferred from these raw and derived radar fields was then compared in time and space to the measured surface electric field, cloud-to-ground (CG) and total lightning flash rates, and ground strike locations. During Hector’s developing stage, precipitating convective cells along island sea breezes were dominated by warm rain processes. No significant electric fields or lightning were associated with this stage of Hector, despite substantial rainfall rates. Aided by gust front forcing, a cumulus merger process resulted in larger, taller, and more intense convective complexes that were dominated by mixed-phase precipitation processes. During the mature phase of Hector, lightning and the surface electric field were strongly correlated to the mixed phase ice mass and rainfall. Merged convective complexes produced 97% of the rainfall and mixed-phase ice mass and 100% of the CG lightning. As Hector dissipated, lightning activity rapidly ceased. As evidenced from the multiparameter radar observations, the multicell nature of Hector resulted in the continuous lofting of supercooled drops to temperatures between 2108 and 2208C in discrete updraft cores during both the early and mature phases. The freezing of these drops provided instantaneous precipitation-sized ice particles that may have subsequently rimed and participated in thunderstorm electrification via the noninductive charging mechanism.