92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Monday, 23 January 2012
Special Sensor Ultraviolet Limb Imager (SSULI) Observations of the Equatorial Nightside Ionosphere At Solar Minimum
Hall E (New Orleans Convention Center )
Damien H. Chua, NRL, Washington, DC; and C. Coker, K. F. Dymond, S. McDonald, A. C. Nicholas, S. A. Budzien, C. A. Metzler, P. Dandenault, P. Serengulian, P. Walker, and G. S. Bust

We investigate the variability of the equatorial, nightside ionosphere during solar minimum conditions using observations by the Special Sensor Ultraviolet Limb Imager (SSULI) on the Defense Meteorological Satellite Program (DMSP) F18 satellite. SSULI limb profiles of the OI 135.6 nm radiative recombination emission are inverted using a 2-D tomographic code to infer nightside electron density profiles in the equatorial, post-sunset ionosphere near 2000 local time (LT) every 100 minutes. Through its first two years of operation in 2010 and 2011, SSULI/F18 has provided a new perspective on the daily variability of the equatorial ionosphere and the seasonal climatology of this region as we transition out of solar minimum into the rise of the next solar cycle. We find that variations in the low-latitude, nightside electron density have no clear correlation with changes in solar flux, suggesting that the ionosphere is driven more by transport than by daytime production (photoionization). During this period, the most prominent departures to the daily and seasonal variations in the low-latitude ionosphere are associated with quasi-periodic geomagnetic disturbances driven mainly by solar co-rotating interaction regions (CIRs). For most of these ionospheric disturbances we observe significant increases in electron density at all altitudes but find little evidence of uplift in the F-layer, suggesting that penetration electric fields are not playing a strong role in shaping the equatorial, post-sunset ionosphere at these times. The SSULI electron density reconstructions are compared to output from the IDA4D assimilative model of the ionosphere to provide further insight into the short term and seasonal variability of the equatorial, nightside ionosphere during these solar minimum conditions.

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