Eos, Transactions American Geophysical Union

Induced particle precipitation



Preliminary results were recently reported from the Navy's Stimulated Emission of Energetic Particles (SEEP) satellite regarding detection of stimulated magnetospheric electron precipitation from ground based Navy VLF transmitters (Eos, January 18, 1983). The results, first released at the AGU Fall Meeting, were obtained on passes during mid-August 1982, using coded transmitter pulses with a duty cycle of 3 s ‘on,’ 2 s ‘off.’

We note here that a similar experiment was conducted by the National Aeronautics and Space Administration (NASA) using low-cost, recoverable rocket payloads from Wallops Island, Virginia, during late June and early July 1982. These flights also used the Navy VLF transmitter (NSS) at Annapolis, Maryland, with the same coding as that used for the later SEEP experiment. Participants in the NASA experiment included scientists from Goddard Space Flight Center, Denver University, and Cornell University. The results of this experiment, also reported at the AGU Fall Meeting, show evidence for pulsed electron precipitation patterns with the same period as the transmitted VLF pulses. These results were accomplished by sensing the bremsstrahlung X rays produced when the electrons reenter the atmosphere. A zenith-viewing, wide angle X ray detector was stabilized with a slow descent aboard a parachutehung payload; this permitted a statistical build-up of the X ray signals over thirty 5-s cycles, a benefit not afforded by a fast moving satellite. Cross correlation analyses of the X ray data with the transmitted signal clearly demonstrated the existence of this effect at a detectable level under nighttime conditions. The SEEP results, which measured the precipitating electrons in situ, are consistent with these earlier NASA findings.