Modeling the ionospheric E and F1 regions: Using SDO-EVE observations as the solar irradiance driver

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ABSTRACT

[1] Over the altitude range of 90–150 km, in dayside nonauroral regions, ionization is controlled almost entirely by solar ultraviolet irradiance; the response time for ionization during solar exposure is almost instantaneous, and likewise, the time scale for recombination into neutral species is very fast when the photoionizing source is removed. Therefore, if high-resolution solar spectral data are available, along with accurate ionization cross sections as a function of wavelength, it should be possible to model this ionospheric region with greater accuracy. The Extreme Ultraviolet Variability Experiment (EVE) instrument on the National Aeronautics and Space Administration Solar Dynamics Observatory (SDO) satellite, launched in February 2010, is intended to provide just such solar data, at high resolution in both wavelength and time cadence. We use the Utah State University time-dependent ionospheric model to assess the sensitivity in modeling that this solar irradiance data provide, under quiet solar conditions as well as during X-class flares. The sensitivity studies show that the E and F1 regions, as well as the valley region, are strongly dependent upon wavelength in both electron density and ion composition.

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