Lightning Sculped by the Thundercloud

Optical emissions from lightning interact with the cloud through absorption and scattering. In some cases, the shape of the flash recorded by LIS follows the geometry of the cloud measured by the other TRMM instruments. We use the meteorological instrumentation on TRMM to improve our understanding of how lightning signals are modified by the surrounding thunderclouds.

Why do lightning flashes illuminate the clouds in the way they do? Some flashes produce bright stationary optical pulses that illuminate a large fraction of the storm. Others are dim and move around in the cloud as they evolve. The Lightning Imaging Sensor (LIS) onboard the Tropical Rainfall Measuring Mission (TRMM) satellite surveyed lightning flashes of all shapes, sizes, and radiances across the tropics.

Because LIS is an optical imager, however, it is unclear to what extent the observed characteristics of LIS flashes are influenced by scattering in the surrounding cloud. Fortunately, the TRMM sensor package includes a variety of instruments for characterizing the lightning‐producing storm. These include a Visible and Infrared Scanner (VIRS), Microwave Imager (TMI), and Precipitation Radar (PR).

This study integrates data from these instruments with LIS to construct a database of cloud regions that are illuminated by lightning. This Illuminated Cloud Feature (ICF) database allows the optical energy from lightning that is observed by LIS to be related to the radar structure and microphysics of the parent thunderstorm. The ICF database is used to identify exotic types of lightning and to show that oceanic lightning flashes are more radiant than flashes over land even when they occur in similar clouds.