Precipitation of hot protons from a stretched near-earth current sheet
Abstract
Recent observational evidences indicate that the near-Earth tail current sheet at approximately ten earth radii often experiences substantial and sudden changes which some researchers consider to be related to the substorm expansive phase onset. Observations of the ionosphere have revealed that auroral substorm activity is often preceded by an enhancement of precipitation of >20 keV protons causing Hβ emissions. Protons in this energy range are most likely to be found in the near-Earth plasma sheet, giving support to the interpretation of a near-Earth source of substorm onset. However, the reason why proton precipitation intensifies during the auroral substorm has not yet been clarified. We propose that a possible explanation of this observation lies in the nonadiabatic dynamics of energetic protons in the stretched near-Earth current sheet formed in the late growth phase of the substorm. While pitch-angle scattering associated with such nonadiabatic dynamics has been considered before, there have been few studies which determine quantitatively how this process might contribute to proton precipitation. We have carried out numerical integrations of proton orbits in a magnetic field consisting of the Earth's main field and that due to a Harris current sheet. We find that, in the regime of highly nonadiabatic dynamics, the proton precipitation rate can exceed the already strong limit of isotropically filled loss-cone precipitation by an order of magnitude. This finding both contributes to our understanding of nonadiabatic effects on precipitation and fits nicely into the overall scheme of near-Earth onset theory.
- Publication:
-
Magnetospheric Research with Advanced Techniques
- Pub Date:
- 1998
- DOI:
- 10.1016/S0964-2749(98)80026-7
- Bibcode:
- 1998mrat.conf..165L