8/9 February 2012 SDO-EVE and Arecibo ISR Ionospheric Capaign

The NASA SDO-EVE solar irradiance observations provide unprecedented high resolution in both time cadence and wavelength. The irradiance wavelengths of the highest importance in driving the altitude structure of the E- and F1-regions lie in two bands, a short wavelength XUV, 2 to 20 nm, and an EUV band from about 80 to 103 nm. Because of the low altitude of the E-region, 100-120 km, only remote sensing techniques are able to observe this region. Two main observational techniques are ionosondes and incoherent scatter radars (ISR). However, only the ISR can distinguish the critical valley region between the E- and F1-regions. A first EVE Arecibo ISR campaign was held on 8/9 February 2012. During daylight hours in the Puerto Rico sector the NSF Arecibo ISR operated in a special high resolution altitude mode through the ionosphere's E- and F1-regions. A total of 22 altitude profiles were obtained. The SDO-EVE instrument also operated its full instrument complement during these daylight hours. In terms of geomagnetic activity and solar dynamics, the entire period was very quiet. This study uses the USU Time Dependent Ionospheric Model (TDIM) to explore the challenges of modeling the E- and F1-region under these quiet conditions. The full irradiance, with excellent wavelength resolution, defines the major input to the TDIM. The Arecibo ISR observations provide the ground truth with both excellent plasma line electron density calibration and better than 1 km altitude resolution. The major objective of this first study is to determine both the sensitivity of the model to various other drivers such as photoelectron secondary ionization, [NO], neutral winds, and the neutral atmosphere as represented by a standard thermosphere model, i.e. MSIS86 and determine what is a necessary ISR observation altitude resolution for the E- and F1-region studies. Additional complications are observed in this dataset including a descending layer and also occurrence of sporadic E. Neither of these features are modeled by the TDIM.