Exploring the role of ionospheric drivers during the extreme solar minimum of 2008
Abstract. During the recent solar minimum, solar activity reached the lowest levels observed during the space age, resulting in a contracted atmosphere. This extremely low solar activity provides an unprecedented opportunity to understand the variability of the Earth's ambient ionosphere. The average E × B drifts measured by the Vector Electric Field Instrument (VEFI) on the Communications/Navigation Outage Forecasting System (C/NOFS) satellite during this period are found to have several differences from the expected climatology based on previous solar minima, including downward drifts in the early afternoon and a weak to non-existent pre-reversal enhancement. Using SAMI2 (Sami2 is Another Model of the Ionosphere) as a computational engine, we investigate the effects of these electrodynamical changes as well as the contraction of the thermosphere and reduced EUV ionization on the ionosphere. The sensitivity of the simulations to wind models is also discussed. These modeled ionospheres are compared to the C/NOFS average topside ion density and composition and Formosa Satellite-3/Constellation Observing System for Meteorology, Ionosphere, and Climate average NmF2 and hmF2. In all cases, incorporating the VEFI drift data significantly improves the model results when compared to both the C/NOFS density data and the F3/C GOX data. Changing the MSIS and EUVAC models produced changes in magnitude, but not morphology with respect to local time. The choice of wind model modulates the resulting topside density and composition, but only the use of the VEFI E × B drifts produces the observed post-sunset drop in the F peak.