Inverse cascade feature in current disruption

摘要

[1] We investigate the origin of waves leading to current disruption and dipolarizationobserved by a THEMIS satellite at XGSM —8 RE in the magnetotail near a substormexpansion onset on 29 January 2008. Continuous wavelet transform of the magneticactivity associated with current disruption shows a clear inverse cascade feature of wavesstarting at frequencies slightly below the ion cyclotron frequency to waves at lowfrequencies that correspond to the time scale of dipolarization. There was no other low-frequency wave associated with the time scale of dipolarization. On the basis of thisinverse cascade feature, we provide a preliminary theoretical analysis to propose thatthe initial excited waves causing eventual dipolarization in this event may originate fromthe drift-driven electromagnetic ion cyclotron instability, which is an electromagneticversion of the Weibel instability, or an ordinary mode instability similarly driven by thecross-field ion drift.