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Kelvin-Helmholtz waves at the Earth's magnetopause: Multiscale development and associated reconnection

Kelvin-Helmholtz waves at the Earth's magnetopause: Multiscale development and associated reconnection

Publication date: 04 December 2009

Authors: Hasegawa, H. et al.

Journal: J. Geophys. Res.
Volume: 114
Issue: A12
ID: A12207
Year: 2009

Copyright: American Geophysical Union

We examine traversals on 20 November 2001 of the equatorial magnetopause boundary layer simultaneously at ~1500 magnetic local time (MLT) by the Geotail spacecraft and at ~1900 MLT by the Cluster spacecraft, which detected rolled-up MHD-scale vortices generated by the Kelvin-Helmholtz instability (KHI) under prolonged northward interplanetary magnetic field conditions. Our purpose is to address the excitation process of the KHI, MHD-scale and ion-scale structures of the vortices, and the formation mechanism of the low-latitude boundary layer (LLBL). The observed KH wavelength (>4 x 104 km) is considerably longer than predicted by the linear theory from the thickness (~1000 km) of the dayside velocity shear layer. Our analyses suggest that the KHI excitation is facilitated by combined effects of the formation of the LLBL presumably through high-latitude magnetopause reconnection and compressional magnetosheath fluctuations on the dayside, and that breakup and/or coalescence of the vortices are beginning around 1900 MLT. Current layers of thickness a few times ion inertia length ~100 km and of magnetic shear ~60° existed at the trailing edges of the vortices. Identified in one such current sheet were signatures of local reconnection: Alfvénic outflow jet within a bifurcated current sheet, nonzero magnetic field component normal to the sheet, and field-aligned beam of accelerated electrons. Because of its incipient nature, however, this reconnection process is unlikely to lead to the observed dusk-flank LLBL. It is thus inferred that the flank LLBL resulted from other mechanisms, namely, diffusion and/or remote reconnection unidentified by Cluster.

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