Jasmine Sandhu (MSSL/UCL): The Terrestrial Ring Current: Investigating the role of substorms in ring current variability
The terrestrial ring current is observed to experience dramatic and intense variations with significant implications for wider geomagnetic processes. Key impacts include 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.
In this seminar, I will discuss how substorms contribute to and shape the ring current properties. Using ion observations from the Van Allen Probes, I conduct statistical analyses of the ring current energy content and anisotropies. I will show that substorms are associated with a significant enhancement of the ring current energy content (~12% for a typical substorm). For increased solar wind driving the substorm-associated enhancement increases, and multiple substorms occurring in direct succession is more likely. For these cases, substorm dynamics can play a crucial role in substantially energising the ring current.
I also investigate storm time variations using a superposed epoch analysis and conduct a comparison to ring current indices. The results show that ring current indices significantly underestimate the energy content of the ring current. I also demonstrate that there is a significant timing discrepancy, such that the ring current intensity peaks ~12 hours later than predicted by ring current indices. This discrepancy is attributed to substorm activity.
Finally, I present some preliminary results exploring how ring current anisotropy varies during substorms. The analysis shows that the ring current ions experience significant isotropisation following substorm onset. This change can be ascribed to either the properties of the injected and convected population and/or EMIC wave activity. I present a consideration of both factors.