Kinetic Alfvén Eigenmodes and Earth’s Radiation Belts

The Earth’s radiation belts pose an existential risk to spacecraft. A critical consideration for the design and operation of an ever-increasing number satellites and future manned spaceflight missions is the mediation of this risk. This is complicated by extreme radiation belt variability during geomagnetically active times. Understanding the drivers of this variability is therefore desirable yet existing physical mechanisms proposed to account for this variability are often insufficient to explain the rapid rates of change observed. Recent observations from NASA’s Van Allen Probes spacecraft have facilitated major advances in understanding this variability including the discovery of kinetic Alfvén eigenmodes in the inner magnetosphere. These modes, well known in tokamaks, are found to pervade the outer radiation belt during space weather events and in particular throughout those intervals where the most dramatic changes in the radiation belts occur. They are observed with the largest amplitudes of any waves observed in Earth’s magnetosphere. In this presentation we describe the properties of these eigenmodes and demonstrate how they act to drive the transport and energization of relativistic electrons. It is shown that through drift-bounces resonances and scattering these modes can drive variation in radiation belt electron fluxes at rates an order of magnitude larger than existing mechanisms and perhaps account for the enigmatic variability observed.