A Missing Dusk-side Loss Process in the Electron Ring Current

The Earth’s magnetic field traps charged particles which are transported longitudinally around Earth, generating a near-circular current, known as the ring current. While the ring current has been measured on the ground and space for many decades, the enhancement of the ring current during geomagnetic storms is still not well understood, due to many processes contributing to its dynamics on different time scales. The low energy part of the ring current of 10-50 keV is responsible for surface charging effects on spacecraft, potentially causing satellite anomalies.

Here, we show that existing ring current models systematically overestimate the in-situ satellite measurements of the Earth’s night side electron ring current during geomagnetic storms. By analyzing electron drift trajectories during the storm onset, we show that this systematic overestimation of flux can be explained through a missing loss process which operates in the pre-midnight sector. Quantifying this loss reveals that the theoretical upper limit of strong diffusion has to be reached in a broad region of space in order to reproduce the observed flux. We include this missing loss process and show that predictions of electron flux can be significantly improved. Identifying missing loss processes in ring current models is vital to accurately predict storm time dynamics and the associated hazards, that result from a delicate balance of source and loss processes.