In an order to improve the NASA/AF Lightning Launch Commit Criteria (LLCC), an Airborne Field Mill (ABFM) campaign was conducted during the summers of 2000 and 2001 at the NASA Kennedy Space Center (KSC). Microphysical measurements of thunderstorm anvils and decaying debris clouds were made using an instrumented aircraft, and the Patrick Air Force Base (PAFB) 74-C radar provided radar reflectivity data. The KSC field mill network was used to measure the surface electric field at 31 locations, and the relationships between these fields and the radar reflectivity aloft are the focus of this study.

The field mill data were archived at KSC at a sample frequency of 50 Hz and were condensed into one-minute averages. These values were then compared to the radar reflectivity. The radar data was processed using the NCAR-SPRINT program package that produces 1 km gridded data. Column averages of the radar reflectivity (measured in dBZ) were computed for each minute above each field mill location. The volume that was used for the column averages extended to the north, south, east and west of each field mill site at altitudes greater than 5 km. The average of the reflectivity in each of these columns was computed using all reflectivities greater than or equal to –10 dBZ. We compared the box average reflectivity and the surface field in a series of scatter plots.

The focus of this presentation will be on two cloud types: (a) Anvil clouds that are defined in the LLCC as “a stratiform or fibrous cloud produced by the upper level outflow or blow-off from thunderstorms or convective clouds” and (b) debris clouds that are defined as “any cloud, except an anvil cloud, that has become detached from a parent cumulonimbus cloud or thunderstorm, or that results from the decay of a parent cumulonimbus cloud or thunderstorm.” When anvil or debris clouds passed over the field mill network, the column average reflectivities and the average electric fields were compared. The presence of any lightning could complicate the interpretation of the electric field data, so any lightning intervals were eliminated using the Lightning Detection and Ranging (LDAR) system at KSC. The meteorological conditions that produce less than 5 dBZ column average reflectivity and surface fields of 1 kV/m or greater are of particular interest in the LLCC. We found that elevated electric fields and low column average reflectivity were present in about 10% of the data for debris clouds and about 5% of the decaying anvils.