A correlation between auroral kilometric radiation and field‐aligned currents

Abstract

Simultaneous observations of field‐aligned currents (FAC) and auroral kilometric radiation (AKR) are compared from the polar‐orbiting satellites Triad and Hawkeye. The Triad observations were restricted to the evening‐to‐midnight local time sector (1900 to 0100 hours magnetic local time) in the northern hemisphere. This is the region in which the most intense storms of AKR are believed to originate. The Hawkeye observations were restricted to when the satellite was in the AKR ‘emission cone’ in the northern hemisphere and at radial distances ≥7 RE (earth radii) to avoid local propagation cutoff effects. A (R/7RE)² normalization to the power flux measurements of the kilometric radiation from Hawkeye is used to take into account the radial dependence of this radiation and to scale all intensity measurements so that they are independent of Hawkeye's position in the emission cone. Integrated field‐aligned current intensities from Triad are determined from the observed transverse magnetic field disturbances. There appears to be a weak correlation between the AKR intensity and the integrated current sheet intensity of field‐aligned currents. In general, as the intensity of auroral kilometric radiation increases so does the integrated auroral zone current sheet intensity increase. Statistically, the linear correlation coefficient between the log of the AKR power flux and the log of the current sheet intensity is 0.57. During weak AKR bursts (<10−18 W m−2 Hz−1), Triad always observed weak FAC’s (<0.4 A m−1), and when Triad observed large FAC's (≥0.6 A m−1), the AKR intensity from Hawkeye was moderately intense (10−15 to 10−14 W m−2 Hz−1) to intense (>10−14 W m−2 Hz−1). It is not clear from these preliminary results what the exact role is that auroral zone field‐aligned currents play in the generation or amplification of auroral kilometric radiation.