Microphysical Properties and the Decay of Electric Fields in Florida Anvils

Herein we present in-situ observations of particle concentrations and sizes with simultaneous in-situ observations of electric field in thunderstorm anvils over or near Kennedy Space Center Florida. The observations were made at 8 to 10 km altitude from the Univ. of No. Dakota Citation jet aircraft during June 2000 and June 2001 in a project to examine electrical decay time in these anvils. Simultaneous radar reflectivity histories of the storms and anvils were determined using the Patrick Air Force Base WSR74C 5 cm radar. The microphysical observations were made with several different instruments which spanned particle sizes from a few microns to several millimeters, thus from frozen cloud droplets to large aggregates. They show that when electric fields are strong (> 20 kV/m) the entire size distribution of particles is significantly greater than when electric fields are weak (< 1 kV/m). As the aircraft flew from near the convective core of a storm toward the downwind edge of the anvil, particle concentrations in all size ranges gradually decrease. The electric fields decreased much more abruptly than the decrease in particle concentrations and showed much greater variability. Not surprizingly there is not a direct connection between the observed microphysics at a given location and the observed electric field. However, in regions with strong electric fields the microphysical observations showed a surprizing consistency of particle concentrations of all sizes from one storm to another. This consistency may have implications for the decay of electric fields in anvils in the absence of active charge separation and will be discussed.