The Impact of Radial and Non-Radial IMF on the Earth's Magnetopause Size, Shape, and Dawn-Dusk Asymmetry From Global 3D Kinetic Simulations

The boundary between the solar wind and the Earth's magnetosphere, the magnetopause (MP), is highly dynamic. Its location and shape depend on SW dynamic pressure and interplanetary magnetic field (IMF) orientation. We use a 3D kinetic Particle-In-Cell code (IAPIC) to simulate an event observed by THEMIS spacecraft on July 16, 2007. We investigate the impact of radial ((Formula presented.) = (Formula presented.)) and non-radial ((Formula presented.) = (Formula presented.)) IMF on the shape and size of Earth's MP for a dipole tilt of (Formula presented.) using maximum density gradient and pressure balance methods. Using the (Formula presented.) model as a reference (MP at 10.3 (Formula presented.)), we find that for non-radial IMF the MP expands by 1.4 and 1.7 (Formula presented.) along the Sun-Earth (OX) and tilted magnetic equatorial (Tilt) axes, respectively, and it expands by 0.5 and 1.6 (Formula presented.) for radial IMF along the same respective axes. When the effect of backstreaming ions is removed from the bulk flow, the expansion ranges are 1.0 and 1.3 (Formula presented.) and 0.2, and 1.2 (Formula presented.), respectively. It is found that the percentage of backstreaming to bulk flow ions are 16.5% and 20% for radial and non-radial IMF. We also show that when the backstreaming ions are not identified, up to 40% of the observed expansion that is due to backstreaming particles can be inadvertently attributed to a change in the SW upstream properties. Finally, we quantified the temperature anisotropy in the magnetosheath, and observe a strong dawn-dusk asymmetry in the MP location, being more extended on the duskside than on the dawnside.