Dawn-Dusk Asymmetry of the Kelvin-Helmholtz Waves at Earth's Magnetopause: One Solar cycle data

Kelvin–Helmholtz instability (KHI) plays a crucial role in solar wind plasma entry into the magnetosphere during the period of northward interplanetary magnetic field (IMF). Several studies have revealed the existence of dawn-dusk asymmetry of KHI along the Earth's magnetopause. However, the causes for such asymmetry are still speculative. Here we survey 11 years of in situ data from the NASA THEMIS (Time History of Events and Macro scale Interactions during Substorms) and MMS (Magnetospheric Multiscale) missions. We found that Kelvin–Helmholtz waves (KHWs) occurrence rates and locations exhibit a semiannual variation; the rate maximizes at the equinoxes and minimizes at the solstice. The rate varies for different IMF By polarities; it is maximum around the fall equinox for negative IMF By, while it is maximum around the spring equinox for positive IMF By. It is shown that the dawn-dusk and north-south asymmetry can be attributed to both the dipole tilt angle and the polarity of Interplanetary magnetic fields (IMF) By; KHI in the northern hemisphere favors the dawn sector for positive dipole tilt and the dusk sector for negative dipole tilt and vice versa in the southern hemisphere. This phase of dawn-dusk asymmetry is dependent on the IMF By polarities.