Statistical study of the ULF Pc4-Pc5 range fluctuations in the vicinity of Earth's magnetopause and correlation with the Low Latitude Boundary Layer thickness

The main generation mechanisms for the Earth's Low Latitude Boundary Layer (LLBL) are considered to be magnetic reconnection, viscous interactions such as Kelvin-Helmholtz instability and associated plasma mixing and diffusion. We have performed a statistical study of the Ultra Low Frequency (ULF) fluctuation power at the Pc4-Pc5 range using ≈6 years of THEMIS measurements of the plasma velocity and magnetic field. The results reveal a clear dawn-dusk asymmetry showing that the fluctuation power is typically more enhanced in the vicinity of the magnetopause downstream of the quasi-parallel shock. The statistical study of the Vx-component of the plasma velocity indicates that the LLBL is also thicker on the dawn-sector. These results may suggest that the physical mechanisms that provide power in the Pc4-Pc5 range are more effective on the dawn-sector and provide a means for a more effective LLBL generation.