In-situ observations of magnetospheric electron scattering by a VLF transmitter

High resolution pitch angle measurements of outer zone electrons in the energy range 12 keV-1.6 MeV were obtained at high altitude in the area of the Soviet VLF high power transmitter UMS (300 kW radiated at 17.1 kHz) while a resonant wave-particle interaction was in progress. More complementary electron measurements in the range of 36-316 keV were obtained in the drift loss cone by another satellite at low altitude along the drift path 75 degrees east of the interaction area. These data indicate that UMS precipitates electrons through a cyclotron mode wave particle interaction in the outer zone. It is further indicated that UMS precipitates electrons through a cyclotron mode wave-particle interaction well down the field line from the equator.