Comparison of Narrow Bipolar Events with Ordinary Lightning as Proxies for the Microwave-Radiometry Ice-Scattering Signature

Abstract

The narrow bipolar event (NBE) is a unique lightning discharge that has a short (?10 ?s) overall duration, lacks a prior leader phase, and produces too little light output to be visible by optical lightning detectors on satellites. NBEs thus have basic differences from ordinary lightning discharges, which occur in flashes lasting up to a fraction of a second, carry significant current in a ?stroke? only after a leader stage that prepares the conductive channel, and produce copious light that is recordable from space. Thus, the authors are motivated to determine whether the meteorological setting of NBEs differs from, or is similar to, that of ordinary lightning. A previous paper started this project of comparing NBEs with ordinary lightning by comparing the placement of either type of lightning within spatial structures of cloud depth, as revealed by infrared cloud-top temperature. That previous study employed lightning data from the Los Alamos Sferic Array (LASA) in Florida. The present paper extends this approach to comparing LASA NBEs with ordinary lightning events? spatial relationships to radiometric cloud imagery from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) 85-GHz channels. This form of radiometric imagery reveals the location of deep, active convective cores with more acute spatial selectivity than does the infrared cloud-top temperature. It was found that the behaviors of NBEs and ordinary lighting are, once again, indistinguishable, but with regard this time to proximity to deep convective cores as revealed by TMI.