Relationship between X‐Ray, ultraviolet, and kilometric radiation in the auroral region

Abstract

An investigation is made of the simultaneous emission of X‐ray and UV photons as a function of time and location in the auroral oval, and comparisons are made of their time variations with the intensity variations of Auroral Kilometric Radiation (AKR). The X rays were measured with the Polar Ionospheric X‐ray Imaging Experiment (PIXIE) instrument on the Polar satellite, and ultraviolet emissions were acquired with the UVI instrument also on the Polar satellite. AKR was measured using the Plasma Wave Instrument (PWI) carried on the Geotail satellite. For the events studied the time profiles of AKR were compared with those of electron precipitation into the auroral atmosphere as measured by the emission of X rays and ultraviolet radiation. The latter emissions exhibited fluctuations which on a scale of minutes to tens of minutes were coherent over several hours of magnetic local time (MLT). The polar region images of X‐ray and UV emissions were usually very similar. The cross‐correlation coefficients between X‐ray and ultraviolet emissions were as high as 0.8 over a wide range of MLT, indicating that the time variations of these different emissions were similar, although the UV observations were limited to the nightside of the Earth and to the field‐of‐view of the UVI. The correlation coefficient between AKR and precipitation as a function of the MLT of the precipitation often exceeded 0.8, usually near midnight, but was >0.5 over several hours of MLT. This widespread correspondence of AKR and precipitation fluctuations is traced to the large‐scale coherence of precipitation fluctuations around the auroral oval.