Relationships between ground charging and radar-determined precipitation band structure in continental winter cyclones

Thundersnow is a rare event that occurs when there is a lightning discharge during a snowstorm. The lightning is usually generated when bands form in the wraparound region of extratropical cyclones. The nature of the electric charge in wintertime precipitation bands is unknown. During the Profiling Of Winter Storms (PLOWS) project, the surface electric field was measured using an electric field mill (EFM). The EFM was collocated with the University of Alabama Huntsville Mobile Integrated Profiling System (MIPS) and was typically deployed in the warm frontal or wraparound regions of passing cyclones. Included with the MIPS was a vertically pointed profiling radar that was used to derive detailed structure of the bands passing overhead.

Data on the locations of the lightning strokes in the vicinity of the MIPS were taken from the National Lightning Detection Network (NLDN). WSR-88D Level II radar data, the MIPS profiling radar, special soundings, and a microwave radiometer were used in conjunction with the NLDN to determine when precipitation bands were in the vicinity of the MIPS EFM, how much lightning was occurring, whether perturbations in the surface electric field occurred during band passages, and what the stability conditions were at the time of the charge measurements. Cases that are being examined include ones with only a few strokes, for determining the lower bound of instability needed for discharges. These are compared with cases with large numbers of confirmed strokes.

In this presentation, the relationship between the field mill measurements and band passages, and the correlation of electric field change to profiler and radiometer measured variables such as cloud liquid water, snow-to-liquid ratio, and particle vertical velocities will be shown.