Global UltraViolet Imager

Solar cycle variations of thermospheric O/N <sub>2</sub> longitudinal pattern from TIMED/GUVI

<p>Thermospheric composition (O/N<sub>2</sub> ratio) is well known to have a great impact on the variation of daytime ionospheric electron density. This study aims to investigate the local time, seasonal, and solar cycle variations of the O/N<sub>2</sub> longitudinal pattern in both hemispheres during daytime in solstices. The O/N<sub>2</sub> data used are from TIMED/Global Ultraviolet Imager observations made over a solar cycle for geomagnetically quiet conditions. The main findings are as follows: (1) The O/N<sub>2</sub> longitudinal patterns are generally similar during 10:00\textendash14:00 LT and between solar minimum and maximum, although the O/N<sub>2</sub> values change with local time and solar cycle. (2) The winter O/N<sub>2</sub> subauroral enhancement is unexpectedly smaller in the longitudes where the magnetic pole is (near-pole longitudes), rather than in the longitudes far from the magnetic pole, especially during solar maximum, and consequently, the longitudinal pattern of O/N<sub>2</sub> depends on latitude in local winter. (3) The winter O/N<sub>2</sub> subauroral enhancement generally moves to more poleward latitudes during solar maximum, as compared to solar minimum. (4) At higher midlatitudes (~45\textdegree\textendash60\textdegreeN and ~40\textdegree\textendash50\textdegreeS in geographic latitudes) in solar minimum, the winter-to-summer ratio of O/N<sub>2</sub> in each hemisphere has an obvious minimum in near-pole longitudes. This minimum becomes more evident during solar maximum. The National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model simulations indicate that in the winter hemisphere, the unexpected O/N<sub>2</sub> longitudinal pattern in higher midlatitudes is mainly associated with high-latitude Joule heating under the impact from ion convection and auroral precipitation.</p>
Year of Publication
Journal of Geophysical Research: Space Physics
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