Auroral kilometric radiation from field-aligned plasma density enhancements.

A production mechanism for left-polarized ordinary auroral kilometric radiation (LOAKR) is proposed on the basis of published satellite measurements. A mechanism analogous to that described by Jones (1976, 1980, 1981, 1982, 1983) for terrestrial myriametric radiation is examined: electrostatic waves produced near the upper-hybrid resonance frequency are converted to electromagnetic Z-mode radiation and then to LOAKR as they propagate through field-aligned plasma-density gradients. The theoretical framework is introduced; the observations of plasma-density enhancements, upper-hybrid waves, and AKR beaming are summarized; a computer model of a density enhancement and associated ray paths is developed; and the beaming model is applied to interpret satellite data as remote-sensing measurements of AKR source regions. The rapid frequency variation of LOAKR is attributed to the distance of the observing spacecraft and the longitudinal motion of the convecting field-aligned source regions.