The impact of Radial and Quasi-Radial IMF on the Earth's Magnetopause Size and Shape, and Dawn-Dusk Asymmetry from Global 3D Kinetic Simulations

The boundary between the solar wind (SW) and the Earths magnetosphere, known as the magnetopause (MP), is highly dynamic. Its location and shape can vary as a function of different SW parameters such as density, velocity, and interplanetary magnetic field (IMF) orientations. In the present paper, we use a 3D kinetic Particle-In-Cell (IAPIC) code to simulate an event of July 26, 2017, captured by THEMIS spacecraft. We investigate the impact of radial (B = Bx, zero cone angle) and non-radial (cone angle 50◦) IMF on the shape and size of Earths MP for a dipole tilt of 31◦ using both maximum density steepening and pressure system balance methods for identifying the boundary. Relative to the MP reference size from the Shue model (10.3 RE), we find that for nonradial IMF, the MP expands by 1.4, and 1.7RE along the sun-Earth and tilted magnetic axes, respectively, and by 0.5 and 1.6RE for radial IMF along the same respective axes. We also found that this expansion rate becomes 1.0 and 1.3RE and 0.2, an 1.2RE respectively when the effect of backstreaming ions is removed from the bulk flow. In addition, we construct the MP shape along the tilted magnetic equator and the Sun-Earth axes, which shows local expansion sunward and along the flanks. We also investigate the properties of back-scattered ions on the dayside magnetosphere, finding that 16.5% and 20% of solar winds are backstreaming for radial and non-radial IMF. It is remarkable that some backstreaming particles are detected up to ≈20 RE upstream. When the backstreaming ions were singled out, their removal leads to a compression of the MP , thus decreasing its expansion. Finally, we quantified the temperature anisotropy in the magnetosheath, and a strong dawn-dusk asymmetry in the MP location.