Magnetospheric Multiscale: The Path from Magnetic Reconnection to Ultra-relativistic Particles

Abstract:

Observational and numerical modeling evidence demonstrates that magnetospheric substorms are a coherent set of processes within the coupled near-Earth system. This supports the view that substorms are a configurational instability driven by magnetic reconnection. The magnetosphere progresses through a specific sequence of energy-loading and stress-developing states until the entire system suddenly reconfigures. Related long-term studies of relativistic electron 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 relativistic electron 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 (i.e., magnetospheric substorms) are normally a key first step in the acceleration of radiation belt electrons to high energies. A second step is suggested to be a period of powerful low-frequency waves or higher frequency (“chorus”) waves that rapidly heat and accelerate electrons. Hence, 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 storms examined whether associated with high-speed streams or with CME-related events. In this talk, we discuss the observations that pertain to high-energy electron acceleration and transport. We focus especially on new results from the Van Allen Probes (Radiation Belt Storm Probes) mission and the key new data from the MMS mission that confirm and greatly extend these key ideas.