Monday

Substorms are a highly dynamic process that results in the global redistribution of energy within the magnetosphere, which has substantial consequences for both radiation belt and ring current dynamics.

Using ion observations (H+, O+, and He+) from the RBSPICE and HOPE instruments onboard the Van Allen Probes, we evaluate changes in the total ring current energy and temperature anisotropies associated with substorms. We find that, on average, ~ 5% of the total energy released at substorm onset is transferred into the ring current ion population, which increases the ring current energy by 12%. Furthermore, the energy increase is found to depend on whether the substorm is isolated or not.

The spatial variation of the energy enhancement matches that expected from particle injections into the inner magnetosphere, and larger enhancements in the O+ contribution to the energy content compared to the H+ contribution suggest important compositional variations. Finally, ion temperature anisotropy is found, on average, to decrease during the substorm expansion phase, suggesting a transfer of energy driving EMIC wave growth in the inner magnetosphere. These ring current dynamics have important implications for wave-particle interactions and the transport and loss of radiation belt electrons. For example, ring current intensifications weaken the geomagnetic field, which allows significant ULF wave power to access the inner magnetosphere and drive rapid radiation belt electron transport via enhanced ULF radial diffusion. Furthermore, EMIC waves generated by ion anisotropies from substorm injections couple to ultra-relativistic MeV electrons and drives rapid radiation belt electron loss through particle precipitation.