Direct Observation of L-X Mode of Auroral Kilometric Radiation in the Lower Latitude Magnetosphere by the Arase Satellite

Abstract

Previous studies have shown that auroral kilometric radiation (AKR) can play an important role in the magnetosphere-atmosphere coupling and has the right-handed extraordinary (R-X), left-handed ordinary (L-O) and left-handed extraordinary (L-X) modes. However, the L-X mode has not been directly observed in the lower latitude magnetosphere yet, probably because of its very limited frequency range. Here, using observations of the Arase satellite on 6 September 2018, we present an AKR event with two distinct bands (8–20 and 300–1000 kHz) around the location: L = 8 and latitude = −37°. The low (high) band is identified as the L-X (R-X) mode based on the polarization and frequency ranges. Simulations of 3-D ray tracing show that most of ray paths with 14 (11 and 18) kHz pass (miss) the location of Arase, basically consistent with observations. Our study provides direct evidence that the L-X mode can propagate from high latitudes downward to lower latitudes.