Analysis of Solar Irradiance Inputs into the ITM System

Solar input to the ionosphere and thermosphere has long been modeled using readily available proxies such as sunspot number and the flux at radio wavelengths such as F10.7. While such proxies have a long observational history, they are typically averaged over long periods of time (81 days to 1 year), washing out day-to-day variability and the 27-day solar rotation cycle. Additionally, both of the parameters were found to saturate during the recent solar minimum, with the ionosphere and thermosphere contracting more than expected based on the variability of these parameters alone. The recent availability of measurements of EUV and X-ray spectra from SDO and TIMED makes it possible to drive ITM models directly with the solar radiation that heats the neutral gases and ionizes them as plasma. Here we examine several potential solar indices, including He II, Mg c-w, and a new index constructed from TIMED/SEE and SDO/EVE data. In addition, we discuss the feasibility of incorporating these into current ITM models.