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

Details 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

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgra..11412207h&link_type=abstract

Journal of Geophysical Research, Volume 114, Issue A12, CiteID A12207

Physics

Plasma Physics

14

Magnetospheric Physics: Magnetopause And Boundary Layers, Magnetospheric Physics: Mhd Waves And Instabilities (2149, 6050, 7836), Magnetospheric Physics: Magnetic Reconnection (7526, 7835), Space Plasma Physics: Transport Processes, Space Plasma Physics: Turbulence (4490)

Scientific paper

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 × 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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