ELECTRIC-FIELD MEASUREMENTS WITH AN AIRPLANE - PROBLEMS CAUSED BY EMITTED CHARGE

The temporal variation of electric field components deduced from measurements made with airplanes penetrating electrified clouds is often complex, especially when the airplane experiences strong electrical charging. However, unusually simple electric field variations were obtained for penetrations involving severe charging of an airplane on flights over Kennedy Space Center, Florida, on August 19, 1989. Analysis of these results suggests that plumes of ions were emitted from the airplane. The electric field from these plumes was more intense than the ambient field from the cloud at the location of the aft electric field sensor. As a consequence the deduced component of the ambient electric field in the direction of flight was severely distorted. These findings emphasize (1) the importance of careful evaluation of electric field data obtained with airplanes and (2) the need for improved measurements.