Association of electron precipitation with auroral kilometric radiation

Abstract

An examination is made of a large body of auroral X ray and auroral kilometric radiation (AKR) data acquired on the Polar satellite in order to investigate the relationship between these two phenomena on a global scale. A detailed study was made of 14 cases selected with strong X ray and AKR emissions and appreciable time variations. In nearly all cases a maximum in the cross‐correlation coefficient of auroral X rays and AKR occurred for X rays emitted slightly before local midnight, indicating that the AKR sources were concentrated in this magnetic local time (MLT) sector. The correlation is quite strong with coefficients between 0.29 and 0.82. The enhancement in the correlation coefficient generally extends over an MLT interval of 6 hours or less, even though electron precipitation above 2 keV extends over a longer MLT interval. This behavior is consistent with the importance of another factor, such as the presence of plasma cavities, being necessary for AKR production. Owing to statistical uncertainties, it was not possible from apogee data to establish whether the X rays or AKR occurred first during the short enhancements. Higher time resolution was achievable when Polar was near perigee, but AKR propagation to Polar was not assured at this location. During a perigee pass on January 13, 1997, Polar observed an auroral X‐ray enhancement in time coincidence with inverted‐V electrons, upward streaming ions, and enhanced AKR. In this event the inverted‐V potential structure extended over at least 2 hours of MLT and lasted for only l min.