A direct diagnosis of the plasma waves responsible for the explosive energy release of substorm onset
Abstract
During periods where the interplanetary magnetic field has a southward component, reconnection on the dayside magnetopause leads to a build up of magnetic flux in the magnetotail lobes, and the magnetotail acts as a reservoir of plasma and energy. During a substorm this energy is explosively released, leading to the deposition of large quantities of energy into the polar ionospheres and leading to the bright and dynamic substorm aurora. Auroral substorm onset is observed at the equatorward edge of the auroral oval, suggesting that at least some of the processes which play an important role in energy release occur on closed magnetic field lines. Recent work has highlighted that auroral beads embedded within the substorm onset arc grow exponentially through onset, which indicates the action of a plasma instability in this near-Earth region. We use state of the art auroral measurements from the MOOSE (Multi-spectral Observatory Of Sensitive EM-CCDs) imagers to construct an observational dispersion relation of the plasma sheet instability responsible for the beading signature in the aurora. Informed by in-situ measurements of the plasma parameters in the magnetotail and magnetic field modelling, we extend theory to a high beta regime in the near-Earth plasma sheet. The solutions of the warm plasma dispersion relation in this regime show that a shear Alfvén wave instability with small perpendicular scales is consistent with the dispersion relation obtained from auroral observations.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E1658K