THE UPPER THERMOSPHERE AT NORTHERN HIGH LATITUDES DURING THE CURRENT SOLAR MINIMUM

At high latitudes, the thermodynamics of the upper thermosphere have undergone long-term synoptic sampling by ground-based Fabry Perot Interferometers, including the last three minimum phases of the solar cycle. These observations provide neutral winds and temperatures from feeble OI (6300A) airglow emission during Arctic nights that last as long as 24 hours/day. At present during the current solar minimum, the altitude of the peak of this airglow layer is approximately 220 km, based on TIDI spacecraft OI (6300A) airglow observations. Monthly (January) averages of geophysical parameters provide insight into changes in the thermosphere that are directly related to solar conditions (F10.7 solar flux) during the evolution of a solar minimum. The current extended solar minimum has provided an opportunity to observe the thermosphere during a progressively quieter sun: January 2006 to January 2009. At Sondre Stromfjord Greenland, the monthly averaged neutral temperature has dropped from ~1100K to ~800K in January during these years. The magnitude of the average equatorial meridional wind has also decreased during this period. Finally, the monthly averaged brightness of OI (6300A) airglow has decreased by ~50% from 2006 to 2009. This paper will place the current solar minimum observations at Sondre Stromfjord into context with previous solar minima measurements. At midnight, this site is typically within the polar cap though it often lies beneath the auroral oval at dusk and dawn. Comparisons with observations in Alaska and Scandinavia will provide a context against other northern geomagnetic locations.