Kelvin-Helmholtz Unstable Magnetotail Flow Channels: Deceleration and Radiation of MHD Waves

Abstract:

The Kelvin-Helmholtz instability (KHI) of magnetotail flow channels associated with bursty
bulk flows (BBFs) is investigated. MHD oscillations of the channel in both kink and sausage modes are
investigated for KHI, and both the primary and secondary KHIs are found that drive MHD waves. These
instabilities are likely to be important for flow channel braking where the KHI removes energy from the flow.
At flow speeds above the peak growth rate, the MHD modes excited by KHI develop from surface modes
into propagating modes leading to the radiation of MHD waves from the flow channel. The coupling of
BBF-driven shear flow instabilities to MHD waves presented here represents a new paradigm to explain BBF
excitation of tail flapping. Our model can also explain, for the first time, the generation mechanism for the
observations of waves propagating toward both flanks and emitted from BBF channels in the magnetotail.