Presentation #207.01 in the session Solar X-ray and VUV Spectra: Observation, Modeling and Planetary Atmospheric Impacts I.
Forecasting the future state of the ionosphere is a fundamental challenge for near-space environment research and operations. In pursuit of this goal, the international space weather community recognizes the need for enhanced fundamental understanding of space weather and its drivers and for improved predictive models of various ionospheric and thermospheric parameters. We have developed a preliminary formulation of high-resolution empirical model of local total electron content (TEC) and investigated different representations of the solar ionizing flux in order to determine the solar flux proxy most suitable for TEC. The model is constructed for middle latitudes using 20 years of high-resolution TEC observations from the CEDAR Madrigal database (2000–2019) and uses multiple temporal delays (ranging from 24 h to 36 days for solar flux and from 3 to 72 h for geomagnetic activity) to describe TEC dependence on solar EUV and geomagnetic activity. Our study examined 11 descriptions of solar flux surrogates and measurements (TIMED SEE EUV, SOHO EUV, F10.7, the Mg II core-to-wing ratio, the Lyman-alpha composite, S10.7, raw S10.7, corrected F10.7, P10.7, E10.7, and FISM2 EUV) for two time periods, 2000–2019 and 2002–2019, using the same formulation of the empirical model. Our results indicate that the FISM2 EUV index performs the best, closely followed by the S10.7 index, the F10.7 proxy, and the Mg II index. We will illustrate the use of the model to characterize the background state of the ionosphere and to accurately identify TEC disturbances during several geomagnetic storms. Finally, we will outline unresolved questions in empirical modeling of TEC and electron density.