Electric Field Meter

The electric field meter (EFM) consists of two metallic spheres centered on a 2 m fiberglass pole. One of the two strofoam rhomboid vanes, which are located at either end of the pole, contains a small electric motor that rotates the spheres about the horizontal axis at a rate of 2 Hz. The instrument measues the equal and opposite charges induced on the spheres by the electric field; from this charge measurement the magnitude of the electric field can be deduced using an approximation to Gauss' Law. Air motion past the rhomboid vanes causes rotation about the vertical axis at a rate of approximately 0.08 Hz and results in a signal modulation from which the horizontal and vertical components of the electric field may be discriminated. The EFM is launched on a 1200 gram balloon and the data is received and recorded by a National Severe Storms Laboratory mobile laboratory.