The L shell region of importance for waves emitted at ground level as a loss mechanism for trapped electrons > 68 keV

The objective of this paper is to identify the L shell region(s) where VLF waves emitted at ground level may play a significant role as a loss mechanism for radiation belt electrons with energies above 68 keV. This assessment is made possible by studying the day-night differences in inner belt electron precipitation and comparing with the much stronger transmission of waves at frequencies of 15--25 kHz through the ionosphere at night and the known higher daytime intensities for waves of natural origin other than lighting. Intensities of electrons trapped on drill shells which dip below sea level in the anomaly are used to study the rates of loss from the radiation belts. In 1979 the inner radiation belt was shown to have had the following unique features for electrons >68 keV: (1) the rates of precipitation from the radiation belts at longitudes west of 140/sup 0/E were significantly greater near midnight than near noontime for Lroughly-equal(1.6-2.2); (2) at Lroughly-equal1.75 the nighttime rates of injection showed little correlation with the precipitation on other L shells, in contrast with the daytime precipitation in which a significant correlation existed with the precipitation rates throughout the range L = 1.2-5.0. From these empirical findingsmore » one concludes that in the heart of the inner radiation belt at longitudes west of 140/sup 0/E, lightning and/or transmitter-generated VLF waves emitted from ground level probably played a significant role in precipitating electrons >68 keV at nighttime. Below the region L = 1.6 and above L = 2.2 the observed diurnal variations were much less pronounced, indicting that VLF waves emitted at ground level in this frequency range were not the major source of precipitation.« less