Global hybrid simulation of mode conversion at the dayside magnetopause

Abstract

Mode conversion at the magnetopause has been suggested to lead to the generation of kinetic Alfvén waves (KAWs) and effective mass transport from the solar wind into the magnetosphere. To investigate the mode conversion process in the dynamic dayside system, a 3‒D global hybrid simulation associated with a quasi‒parallel shock under a radial interplanetary magnetic field (IMF) is carried out, in which the foreshock compressional pulses are self‒consistently generated by the interaction between the solar wind and the geomagnetic field. The results show that as the compressional pulses propagate from the magnetosheath to the magnetopause, short‒wavelength structures of k⊥ρi∼0.5–1 with enhanced parallel electric field E∥ are excited in the subsolar magnetopause boundary layer (MPBL), where k⊥≃kx is the perpendicular waves number nearly along the GSE x direction, and ρi is the ion Larmor radius. The wave‒phase relationship between the magnetic field and the density changes from in‒phase in the magnetosheath to antiphase in the short‒wavelength MPBL perturbations. The wave polarization is predominantly compressive in the magnetosheath, whereas strong transverse wave powers appear abruptly around the MPBL. The mode conversion from the compressional pulses to KAWs is identified around the predicted Alfvén resonance surface in the MPBL. As these KAWs evolve, KAW modes dominated by azimuthal wave number with kyρi∼1 are also generated. The KAWs in the MPBL are identified by the sharp increases in E∥ and the electromagnetic field polarization relations of Alfvén mode, as well as a spectral analysis. The KAW perturbations propagate poleward into the cusps along the MPBL. Due to the differential flow convection speeds at various latitudes, the KAW packets expand along the north‒south direction, while they may also merge with newly‒formed KAWs due to newly‒arrived compressional waves.