Magnetospheric Response to Solar Wind Forcing -ULF Wave - Particle interaction Perspective

Sudden changes in solar wind forcing, e.g., those associated with interplanetary shocks and/or solar wind dynamic pressure pulses, can cause many fundamentally important phenomena in the Earth’s magnetosphere including electromagnetic wave generation, plasma heating and energetic particle acceleration. This presentation summarizes our present understanding of the magnetospheric response to solar wind forcing in the aspects of radiation belt electrons, ring current ions and plasmaspheric plasma based on in situ spacecraft measurements, ground-based magnetometer data, MHD and kinetic simulations. 

Magnetosphere response to sudden changes in solar wind forcing, is not a “one-kick” scenario. It is found that after the impact of solar wind structures on the Earth’s magnetosphere, plasma heating and energetic particle acceleration started nearly immediately and could last for a few hours. Even a small dynamic pressure change associated with an interplanetary shock or a solar wind pressure pulse can play a non-negligible role in magnetospheric physics. The impact leads to different kinds of waves including poloidal mode ULF waves. The fast acceleration of energetic electrons in the radiation belt and energetic ions in the ring current region usually contains two steps: (1) the initial adiabatic acceleration due to the magnetospheric compression; (2) followed by the wave-particle resonant acceleration dominated by global or localized poloidal ULF waves excited at various L-shells. 

Generalized theory of drift and drift-bounce resonance with growing or decaying ULF waves  (globally distributed or localized)  has been developed to explain in situ spacecraft observations. The new wave-related observational features like distorted energy spectrum, boomerang and fishbone pitch angle distributions of radiation belt electrons, ring current ions and plasmaspheric plasma can be explained in the frame work of this generalized theory. The results showed in this presentation can be widely used in the interaction of the solar wind with other planets such as Mercury, Jupiter, Saturn, Uranus and Neptune, and other astrophysical objects with magnetic fields.