Statistical Study on Spatial Distribution of Frequency‐Chirping ECH Elements by Van Allen Probes

Abstract

Abstract Electron cyclotron harmonic (ECH) waves can scatter electrons into the atmosphere causing diffuse aurora with diffusion coefficients depending on the wave frequency. Here we report the Van Allen Probe observations of chirping ECH elements, which are fine structures with a frequency‐chirping rate of ∼kHz/s. 1,834 samples are identified in the 51‐month database and over 93 percent of them exhibit a falling tone pattern. ECH elements cover a broad region from 18 Magnetic Local Time (MLT) through dawn to 14 MLT with L = 4 − 7, and mainly occur in the region of 00–07 MLT with L = 5 − 6. More ECH elements are observed with the occurrence region extending to lower L‐shells during the geomagnetic activity period. Chirping ECH elements can propagate to |MLAT| ∼ 20°, but be confined by the contour of magnetic field strength. The statistical results can be applied on the global simulation of ECH‐induced electron penetration.

Keywords

• ECH wave
• frequency‐chirping fine structure
• spatial distribution