Correlating Cloud-to-Ground and Intra-Cloud Lightning to DSD Parameters

A suitable relationship between lightning and rainrate has long been sought as a means for improving radar measurements of rain and possibly as a remote rain measurement method in it's own right. Since Battan's 1965 study of the correlation between lightning count and rainfall total, many approaches to the lightning-to-rainfall correlation have been attempted. These have included sorting rain events by storm type or season, as well as classifying lightning according to polarity. Recently, the authors of the present work correlated the density of lightning strokes to measures of the drop size distribution (DSD), thereby correlating lightning to the statistics of raindrop size, as opposed to the rainrate. In that work, the parameters N₀ and Λ, obtained from the usual exponential parameterization of the DSD: N₀ e^{(-Λ D)} were correlated to the density of lightning strokes.

The present work refines the aforementioned approach by first sorting lightning strokes into cloud-to-ground (CG) and intra-cloud (IC) categories, prior to correlation to the DSD parameters. Lightning data for this study were obtained from the Los Alamos National Laboratory EDOTX lightning detection array, located in Northern Florida. The EDOTX array has the ability to classify each detected stroke as CG or IC. The drop size distribution was collected with a Joss-Waldvogel disdrometer located in Citra, FL, close to the center of the EDOTX array. N₀ and Λ were extracted from the disdrometer data. In addition, a tipping bucket rain gage colocated with the disdrometer recorded the rain rate (R). In this presentation, N₀, Λ , and R are each correlated to the total number of strokes (CG + IC), the number of IC strokes, the number of CG strokes, and the percent of strokes which were IC. Averaging intervals of 1 and 24 hours were considered.

Currently being investigated is the use of WSR-88D radar data to improve correlations, as well as the difference between correlations to EDOTX and National Lightning Detection Network (NLDN) data.