Kelvin-Helmholtz Instability at the Magnetopause under Different Solar Wind Conditions: 3D Global MHD Simulations and Statistical Study

Abstract:

Using the PPMLR-MHD global simulation model, we examined the Kelvin-Helmholtz (K-H) instability at the magnetopause for northward interplanetary magnetic field (IMF) conditions with various solar wind speed (400, 600, and 800 km/s). The spatial distribution of the K-H wave power in the equatorial plane shows two distinct power populations, referring to the two modes of K-H surface waves. The K-H instability starts at about 30^o longitude, and grows exponentially with a spatial growth rate of 0.28 ~ 0.87 R_E^-1until ~45^o longitude where the vortices fully develop. The wave frequency, wavelength, and phase speed are also given. The KH wavelength grows spatially with increasing distance from the sub-solar point tail-ward along the flank magnetopause. Model results show that the higher solar wind speed generates K-H waves with higher frequency under the northward IMF, and the wavelengths and the phase speeds increase with the increase of the longitude. Statistically study of the 56 KHI events observed by THEMIS,Geotail, TC-1, Cluster support our simulation predictions.