Observations of the neutral thermosphere during the extended 2008-2009 solar minimum period found anomalously low density, implying that thermospheric temperature was also lower than usual for solar minimum. A variety of solar measurements and proxies indicated commensurately lower levels of solar extreme-ultraviolet (EUV) irradiance, although there remains considerable uncertainty concerning the magnitude of the reduction. Recent model simulations demonstrated that a ~10% decrease in solar EUV from the previous solar minimum, combined with a modest decrease in geomagnetic activity, and a small contribution from long-term global cooling due to increases in anthropogenic carbon dioxide, could explain the neutral density changes. The next question is how this pertains to the ionosphere. Numerous published observational studies have shown that ionospheric densities during 2008-2009 were lower than during previous solar minima, but there was considerable deviation from one location to another, and from one data analysis to another, with one global indicator showing little or no change. This seminar will review model results from the NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM) and the comparison with neutral density changes, and discuss the implications for the ionosphere.
Published on March 4, 2013
Speaker:Stan Solomon (NCAR)