Seasonal and Diurnal variations of KHI at the Earths Magnetopause

We survey one solar cycle of in situ data from the NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) and MMS (Magnetospheric Multiscale) missions to identify KelvinHelmholtz Instability (KHI) along Earths magnetopause flank. We found that KHI occurrence rates exhibit a semiannual and diurnal variations; the rate maximizes at the equinoxes and minimizes at the solstices. The rate varies for different IMF By polarities; it is maximum around fall equinox for negative IMF By, while is maximum around spring equinox for positive IMF By. While the dipole tilt angle explains most part of the seasonal and diurnal variation of KHI, the angle of the Earth's dipole in the plane perpendicular to the EarthSun line explains the difference between KHI occurrence rates with positive/negative IMF By. These results reveal the key role of Sun-Earth geometry on modulating the KHI and thus the time sensitivity of plasma transport across the magnetopause.