Redistribution of H atoms in the upper atmosphere during geomagnetic storms

Abstract
<p>Geocoronal H emission data acquired by NASA\textquoterights Thermosphere Ionosphere Mesosphere Energetics and Dynamics mission are analyzed to quantify the H density distribution over the entire magnetosphere-ionosphere-thermosphere region in order to investigate the response of the atmospheric system as a whole to geomagnetic storms. It is shown that at low and middle latitudes the H density averaged over storm times in the thermosphere-exosphere transition region decreases by \~30\%, while the H density at exospheric altitudes above \~1\textendash2\&nbsp;<em>R</em><sub><em>E</em></sub> increases by up to \~40\% relative to quiet times. We postulate that enhanced ion-neutral charge exchange in the topside ionosphere and inner plasmasphere is the primary driver of the observed H redistribution. Specifically, charge exchange reactions between H atoms and ionospheric/plasmaspheric O<sup>+</sup> lead to direct H loss, while those between thermal H and H<sup>+</sup> yield kinetically energized H atoms which populate gravitationally bound satellite orbits. The resulting H density enhancements in the outer exosphere would enhance the charge exchange rates in the ring current and the associated energetic neutral atom production. Regardless of the underlying mechanisms, H redistribution should be considered as an important process in the study of storm time atmospheric evolution, and the resultant changes in the geocoronal H emissions potentially could be used to monitor geomagnetic storms.</p>
Year of Publication
2017
Journal
Journal of Geophysical Research: Space Physics
Volume
122
Number of Pages
686-10
Date Published
08/2017
ISSN Number
2169-9380
URL
https://onlinelibrary.wiley.com/toc/21699402/122/10
DOI
10.1002/jgra.v122.1010.1002/2017JA024489