MULTILEVEL MEASUREMENT OF THE ELECTRIC-FIELD UNDERNEATH A THUNDERCLOUD .2. DYNAMIC EVOLUTION OF A GROUND SPACE-CHARGE LAYER

In August 1989 the electric field was measured below a thunderstorm at Kennedy Space Center for more than 1 hour at several levels up to 800 m. No substantial precipitation reached the ground at the experimental site until after this data collection period, which included the thunderstorm approach and the triggering of four lightning flashes. The sensors at altitude were suspended from a tethered balloon and that at the surface was a standard field mill. The maximum value detected was 65 kV/m at 603 m while at the same time the steady surface field did not exceed 5 kV/m. Applying Gauss's law to the electric field data, we have calculated average charge densities within the layers formed by the levels where the sensors were located. Corona ions produced at the surface were detected up to the upper layer between 436 m and 603 m, and the densities calculated reached values close to 1 nC m-3 within each layer. The current densities were also evaluated at the sensor levels; the one calculated at 436 m ranges about 1.4 nA m-2 which means that a large proportion of corona ions were carried up to several hundreds of meters above ground.