The modulated precipitation of radiation belt electrons by controlled signals from VLF transmitters

Abstract

The first direct observations of the precipitation of radiation belt electrons by the controlled injection of VLF signals from a ground based transmitter were recently reported from data acquired in the SEEP (Stimulated Emission of Energetic Particles) experiment. That outstanding example of time‐correlated wave and electron data has now been enhanced by the finding of four additional modulated events out of 65 satellite passes when one of the U. S. Navy VLF transmitters at Cutler, Maine (NAA) or at Annapolis, Maryland (NSS) was being modulated in a 3s ON/2s OFF format. During each of these events the fluxes of precipitating electrons were observed repeatedly to display a characteristic time behavior with respect to the transmitter modulation: a relatively slow rate of increase after start of the ON period leading to a maximum about 2 seconds later. Details of this consistent pattern and the statistics of occurrence of modulation events are presented along with comparisons of the absolute fluxes of precipitating electrons observed during normal transmitter operation with those recorded when one of the transmitters was modulated.