Relationship of noise in the frequency range 100 < f < 500 kHz to auroral arcs and field‐aligned current and implications regarding acceleration of auroral electrons

The magnetic signatures of field‐aligned and ionospheric currents can be used to determine the geometry and strength of the electrical current systems which couple the ionosphere to the outer regions of the earth's magnetosphere. It is now recognized that the currents flowing in the evening sector are an important clue to the understanding of processes leading to explosive substorm instabilities and episodes of intense ionospheric disruption. In this report we have used a combination of ground‐based magnetometer data and Isis 2 satellite data in the form of energetic particles, auroral luminosity, and electromagnetic and/or electrostatic noise measurements to provide a comprehensive picture of processes which are taking place on field lines penetrating the auroral oval in the evening and midnight sectors. We shall show that noise measurements in the frequency range 100 < f < 500 kHz are characteristic of regions of upward current flow which are found in the region of discrete auroral features. We find that the higher‐energy electrons (a few keV) are associated with the higher‐frequency noise. In addition, the highest noise frequencies are found in the center of discrete auroral arc regions with the frequency decreasing on either side of the center of the arc region. We believe that the source of noise in this frequency range is associated with electron beams in discrete arcs whose velocity space distribution contains a region of positive slope. We shall finally discuss the physics of the relationship among the various electromagnetic and energetic particle signatures presented in this study.