The Role of Solar and Solar Wind Forcing of Magnetospheric Particle Enhancements

Abstract:

Observational and numerical modeling results demonstrate that solar wind streams and coronal mass ejections drive coherent processes within the coupled magnetosphere-ionosphere system. The magnetosphere progresses through a specific sequence of energy-loading and stress-developing states until the entire system suddenly reconfigures. Long-term studies of high-energy particle fluxes in the Earth’s magnetosphere have revealed many of their temporal occurrence characteristics and their relationships to solar wind drivers. In order to observe major energetic particle enhancements, there must typically be a significant interval of southward IMF along with a period of high (V_SW≥500 km/s) solar wind speed. This has led to the view that enhancements in geomagnetic activity are normally a key first step in the acceleration of magnetospheric particles to high energies. A second step is suggested to be a period of powerful low-frequency waves that is closely related to high values of V_SW or higher frequency (“chorus”) waves that rapidly heat and accelerate electrons. Hence, magnetospheric storms and substorms provide a “seed” population, while high-speed solar wind drives the acceleration to relativistic energies in this two-step geomagnetic activity scenario. This picture seems to apply to most events examined whether associated with high-speed streams or with CME-related changes, but not all. In this work, we address transient solar wind phenomena as they pertain to high-energy particle acceleration and transport. We also discuss various models of particle energization that have recently been advanced. We present remarkable new results from the Van Allen Probes mission and the Magnetospheric Multiscale (MMS) mission that confirm and greatly extend these key ideas.