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 Alfven 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 3D global hybrid simulation associated with a quasiparallel shock under a radial interplanetary magnetic field (IMF) is carried out, in which the foreshock compressional pulses are selfconsistently 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, shortwavelength structures of k(i)approximate to 0.5-1 with enhanced parallel electric field E-vertical bar are excited in the subsolar magnetopause boundary layer (MPBL), where k similar or equal to k(x) is the perpendicular waves number nearly along the GSE x direction, and (i) is the ion Larmor radius. The wavephase relationship between the magnetic field and the density changes from inphase in the magnetosheath to antiphase in the shortwavelength 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 Alfven resonance surface in the MPBL. As these KAWs evolve, KAW modes dominated by azimuthal wave number with k(yi)approximate to 1 are also generated. The KAWs in the MPBL are identified by the sharp increases in E-vertical bar and the electromagnetic field polarization relations of Alfven 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 northsouth direction, while they may also merge with newlyformed KAWs due to newlyarrived compressional waves.