Total Lightning as an Indicator of Mesocyclone Behavior

With the increasing availability of local Lightning Mapping Arrays (LMAs) and the anticipated launch of the Geostationary Lightning Mapper (GLM), many studies have documented the apparent relationship between total (i.e., in-cloud and cloud-to-ground) lightning activity and severe weather. In order to maximize the capabilities of total lightning data for nowcasting severe storms, its fusion with proven tools has become a major goal in the research and operational communities. As such, this study lays some of the groundwork for fusing radar with total lightning into a multi-sensor algorithm for severe weather detection and forecasting. Specifically, Weather Surveillance Radar – 1988 Doppler (WSR-88D) and LMA data are used for an initial investigation of the concept with a focus on tornadic storms.

Some of the recent work assessing the effectiveness of lightning as an operational tool has led to the development of lightning jump algorithms, relating rapid increases in total lightning flash rates to severe phenomena. The algorithm is based upon the microphysical and kinematic connection between storm electrification and dynamics. In particular, for both charge separation leading to flash initiation and mesocyclogenesis, the updraft plays a pivotal role. For example, a low-to-mid-level updraft that is responsible for flash production could also contribute to the tilting of environmental horizontal vorticity into the vertical, the subsequent stretching of this vertical vorticity, and the development and intensification of a mesocyclone. Because of this relationship, it is possible that lightning may provide an early indication of changes in updraft strength that relate to and can give some indication of the development or strengthening of a storm's mesocyclone.

Better understanding of this relationship could assist forecasters issuing warnings in discerning between severe and potentially tornadic storms, particularly for the first warned storm of an event. Case studies of severe weather events are used to explore the hypothesis that total lightning activity can offer additional insight into mesocyclone development and associated tornado potential. These studies include analysis of LMA data and WSR-88D mesocyclone detection output from the operational National Severe Storms Laboratory (NSSL) Mesocyclone Detection Algorithm (MDA). Lightning jumps as well as other trends in lightning flash rate are observed alongside occurrence, maintenance, strengthening, and rotational characteristics of mesocyclone detections. Using these attributes, preliminary results indicate that some relationship does exist between lightning jumps, local maxima in lightning flash rates, and development or strengthening of a storm mesocyclone.