Doppler Radar and Radio Observations of Thunderstorms

Three-dimensional motion fields in a thunderstorm are compared to measurements of the radar reflectivity structure of the storm and to the locations of VHF radiation from electrical discharges, in an attempt to determine the physical conditions which prevailed during the electrically active phase of the storm. The observations were obtained from a network of three Doppler radars and a long-baseline radiation source location system during the 1978 Thunderstorm Research International Program (TRIP 78) at Kennedy Space Center, FL. The analysis shows that two cells developed sequentially on the upshear side of the storm. In the second cell, the updraft velocity between 6- and 7-km altitude (-10 to -15°C) increased rapidly to greater than 20 ms-1; and coincided with a substantial increase in the VHF radiation burst rate. Growth of the updraft was accompanied by the simultaneous development of an upper level downdraft on its upshear side. Reflectivity values in excess of 50 dBZ were observed within the vicinity of the updraft, and have been attributed to graupel or hail that was suspended in the updraft and which grew by riming of supercooled water droplets. Initial source locations for each radiation burst formed an umbrella-like pattern above the high-reflectivity core. We interpret the results to be consistent with an ice-ice electrical charging interaction first investigated by Reynolds et al.