The lightning activity of a hailstorm as a function of changes in its microphysical characteristics inferred from polarimetric radar observations

The progression of cloud‐to‐ground (CG) lightning activity in an Oklahoma hailstorm with well‐developed supercell organization is related to changes in the microphysical characteristics of the storm as inferred from polarimetric radar observations. A decision tree based on the observed values of radar reflectivity Z H , differential reflectivity Z DR , and specific differential phase K DP is used to identify regions in the storm containing graupel, hail, supercooled liquid water, and rain. Mixing ratios of graupel/hail and liquid water are obtained in terms of Z H , Z DR , and K DP . One of the objectives of the study is to relate the development of graupel aloft, and the descent of graupel and hail, to fluctuations in CG lightning production. The results indicate that the development of graupel above the freezing level is related to the overall increase and decrease in the production of CG flashes (probably by providing the negative charge necessary for the flashes). However, it is the fluctuating descent of small hail below the height of the negatively charged graupel region that is correlated with the three or four pulses in the CG lightning activity (apparently by producing the electric bias needed for the discharge of the graupel layers aloft).