Auroral kilometric radiation - Time-averaged source location

The location of the average generation region of auroral kilometric radiation is found by studying average electric field strengths as a function of spacecraft position in narrow frequency bands centered at 178, 100, and 56.2 kHz. A combined 5 years of data from the University of Iowa plasma wave experiments on satellites Hawkeye 1 and Imp 6 provide the basis for determining the average electric field strengths. Hawkeye 1 was in a highly elliptical, polar orbit with an apogee near 21 RE over the northern polar region, and Imp 6 was in a highly elliptical, near-equatorial orbit with an apogee of 33 RE. Together these satellites provide extensive coverage from 3 to 21 RE in the northern hemisphere and inside of 3 RE in the southern hemisphere. Intense sources of auroral kilometric radiation are found in the northern and southern hemispheres. Their locations are near 65° invariant latitude in their respective hemispheres, between 22 and 24 hours magnetic local time, and near 2.5 RE. The total time-averaged power generation is found to be about 107 W, assuming a spectral bandwidth of 200 kHz. Propagation effects limit the emission cone of auroral kilometric radiation in a given hemisphere to roughly 4.1 sr at 178 kHz, 2.2 sr at 100 kHz, and 1.5 sr at 56.2 kHz. Evidence that the polar cusp region is illuminated at distances as close as 4 RE suggests the possibility that previously observed polar cusp sources are the result of scattering from field-aligned density irregularities.