Observational Evidence for Three Time‐Scale Modulations in the Pulsating Aurora

Abstract

We report an Arase-all sky imager (ASI) conjugate event in which the pulsating aurora (PsA) has a one-to-one correspondence with chorus bursts. Wavelet analysis displayed three peaks at --0.3 Hz, 4 Hz, and >10 Hz, corresponding to the main pulsation, internal modulation, and fast modulation, respectively. These correspond to the old terms of --5-15 s pulsations, chorus risers/elements and subelements/subpackets, respectively. Electron “microbursts” correspond to the 4-Hz peak. The internal and fast modulations are further verified by the analysis based on fast Fourier transform analyses. Moreover, the spatial distributions of the Fourier spectral amplitude show that the internal and fast modulations are well-structured within auroral patches. The above results indicate a paradigm shift away from quasilinear theory which implicitly assumes diffuse wave generation. The three time-scale modulations are consistent with coherent chorus which has been theoretically argued to lead to pitch angle transport three orders of magnitude faster.