Solar cycle variations of thermospheric composition at the solstices

Abstract
<p>We examine the solar cycle variability of thermospheric composition (O/N<sub>2</sub>) at the solstices. Our observational and modeling studies show that the summer-to-winter latitudinal gradient of O/N<sub>2</sub> is small at solar minimum but large at solar maximum; O/N<sub>2</sub> is larger at solar maximum than at solar minimum on a global-mean basis; there is a seasonal asymmetry in the solar cycle variability of O/N<sub>2</sub>, with large solar cycle variations in the winter hemisphere and small solar cycle variations in the summer hemisphere. Model analysis reveals that vertical winds decrease the temperature-driven solar cycle variability in the vertical gradient of O/N<sub>2</sub> in the summer hemisphere but increase it in the winter hemisphere; consequently, the vertical gradient of O/N<sub>2</sub> does not change much in the summer hemisphere over a solar cycle, but it increases greatly from solar minimum to solar maximum in the winter hemisphere; this seasonal asymmetry in the solar cycle variability in the vertical gradient of O/N<sub>2</sub> causes a seasonal asymmetry in the vertical advection of O/N<sub>2</sub>, with small solar cycle variability in the summer hemisphere and large variability in the winter hemisphere, which in turn drives the observed seasonal asymmetry in the solar cycle variability of O/N<sub>2</sub>. Since the equatorial ionization anomaly suppresses upwelling in the summer hemisphere and strengthens downwelling in the winter hemisphere through plasma-neutral collisional heating and ion drag, locations and relative magnitudes of the equatorial ionization anomaly crests and their solar cycle variabilities can significantly impact the summer-to-winter gradients of O/N<sub>2</sub> and their solar cycle variability.</p>
Year of Publication
2016
Journal
Journal of Geophysical Research: Space Physics
Volume
121
Number of Pages
3740-3749
Date Published
04/2016
URL
http://doi.wiley.com/10.1002/2016JA022390
DOI
10.1002/2016JA022390