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Colorado State Univ.: "NEXRAD and lightning studies"

Final Report

The deployment of WSR-88D Doppler radars, coupled with the existing National Lightning Detection Network (NLDN), offers a new and exciting means of examining cloud dynamics and electrification throughout a large portion of the North American continent. To date, relatively few studies of cloud electrification have been conducted in the western U.S., a region where high-base thunderstorms and associated cloud-to-ground lightning are commonplace in the monsoon months of July-September.

This project used data from the WSR-88D radar located at Phoenix, Arizona and lightning data from the NLDN to examine the evolution and forcing associated with electrified clouds in central Arizona. Specific tasks included:

  1. Identification of specific radar characteristics (e.g., storm mass in the mixed phase region of the cloud, vertically integrated liquid water, echo top height) and synoptic/mesoscale patterns associated with the electrical development (including cloud-to-ground flash rates) and severity of thunderstorms in central Arizona.

  2. Examination of the feasibility of using NEXRAD radar data and NLDN data in future local and large scale storm electrification research.

Two case studies of thunderstorms associated with damaging winds were selected for analysis. For each case, coincident temporal and spatial trends in the cloud-to-ground (CG) lightning, radar reflectivity (with an emphasis on the vertical plane), and radial velocity were examined. The analysis allowed the researchers to 1) examine the coevolution of thunderstorm outflows and reflectivity cores (e.g., microburst winds) with the CG lightning frequency and polarity, and 2) examine the transition from vigorous convection to a stratiform or decaying stage of the convective life cycle concomitant with changes in CG lightning flash frequency and polarity.

A relationship was found between the time of peak CG flash rate and the occurrence of the outflow. The analysis suggests that the trend or slope of the CG flash rate, when coupled with trends in the height of the radar reflectivity core, could provide additional information for damaging wind algorithms being developed and implemented in the WSR-88D derived product software. Another interesting observation was noted for one of the storms in which several separate regions of the convection experienced a very abrupt transition in the polarity of CG lightning from exclusively negative to exclusively positive polarity coincident with what appeared to be a transition from convective to stratiform rainfall.