Spatiotemporal Behavior of Ulf Waves Excited By Interplanetary Shock and Solar Wind Dynamic Pressure Impulses in the Magnetosphere

Abstract:

When an interplanetary shock or a solar wind dynamic pressure impulse impinges on the magnetophere, ultra low-frequency (ULF) waves can be excited in the magnetosphere and the solar wind energy can be transported from interplanetary space into the inner magnetosphere. In this study, we have systematically studied ULF waves excited at in the magnetosphere by interplanetary shock or solar wind dynamic pressure impulse. We have found that the poloidal and toroidal waves excited by positive and negative pressure pulses oscillate in a similar manner of phase near 06:00 local time (MLT) and 18:00 M LT, but in antiphase near 12:00 M LT and 0:00 MLT. ULF waves generated by IP shock impact is much stronger than that to negative pressure pulses. Furthermore, it is shown that excited ULF oscillations are in general stronger around local noon than those in the dawn and dusk flanks. It is demonstrated that the poloidal wave amplitudes are stronger than the toroidal wave amplitudes except in the magnetotail.

In the energetic particle point of view that the magnitude of IP shock generated ULF waves (energetic particle flux oscillations) are much larger around 12:00 LT than at dawn and dusk and oscillate in an opposite phase near local noon and midnight。 A frequency preference in the oscillations in between 2.2 mHz and 3.3 mHz. The oscillations are stronger under southward IMF condition than that under northward IMF condition. Plasmapause /PBL would modify the generated ULF waves.