SA32A-01
The impact of exospheric neutral dynamics on ring current decay

Wednesday, 16 December 2015: 10:20
2007 (Moscone West)
Raluca Ilie1, Michael Warren Liemohn2, Ruth M Skoug3, Herbert O Funsten4, Mike Gruntman5, Justin James Bailey6 and Gabor Toth2, (1)University of Michigan, Ann Arbor, MI, United States, (2)University of Michigan Ann Arbor, Ann Arbor, MI, United States, (3)Los Alamos Natl Lab, Los Alamos, NM, United States, (4)Los Alamos Natl Laboratory, Los Alamos, NM, United States, (5)University of Southern California, Los Angeles, CA, United States, (6)Space Environment Technologies, Huntington Beach, CA, United States
Abstract:
The geocorona plays an important role in the energy budget of the Earth’s inner magnetosphere since charge exchange of energetic ions with exospheric neutrals makes the exosphere act as an energy sink for ring current particles. Long-term ring current decay following a magnetic storm is mainly due to these electron transfer reactions, leading to the formation energetic neutral atoms (ENAs) that leave the ring current system on ballistic trajectories.

The number of ENAs emitted from a given region of space depends on several factors, such as the energy and species of the energetic ion population in that region and the density of the neutral gas with which the ions undergo charge exchange. However, the density and structure of the exosphere are strongly dependent on changes in atmospheric temperature and density as well as charge exchange with the ions of plasmaspheric origin, which depletes the geocorona (by having a neutral removed from the system). Moreover, the radiation pressure exerted by solar far-ultraviolet photons pushes the geocoronal hydrogen away from the Earth in an anti-sunward direction to form a tail of neutral hydrogen.

TWINS ENA images provide a direct measurement of these ENA losses and therefore insight into the dynamics of the ring current decay through interactions with the geocorona. We assess the influence of geocoronal neutrals on ring current formation and decay by analysis of the predicted ENA emissions using 6 different geocoronal models and simulations from the HEIDI ring current model during storm time. Comparison with TWINS ENA images shows that the location of the peak ENA enhancements is highly dependent on the distribution of geocoronal hydrogen density. We show that the neutral dynamics has a strong influence on the time evolution of the ring current populations as well as on the formation of energetic neutral atoms.

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