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

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.

Flares at Earth and Mars: An Ionospheric Escape Mechanism?

“…No values of plasma drift speeds or upward fluxes of plasma were presented. A follow‐up study by Sojka et al () used the same model with improved solar irradiance input to characterize flare effects in the lower ionosphere, with topside results similar to those in Smithtro et al (). Using a fully numerical global model (TIME‐GCM), Qian et al (, ) conducted simulations of ionospheric enhancements ( E layer and TEC) resulting from different locations of flares on the solar disk, as well as differences in flare rise and decay times.…”

CONSTRAINING SOLAR FLARE DIFFERENTIAL EMISSION MEASURES WITH EVE AND RHESSI

“…The wavelength range of ~0.4-5 nm is thought to contain the bulk of flare-radiated energy (Rodgers et al 2006) and is the primary driver of ionospheric dynamics. Very few spectrally resolved observations exist in this range, and the detailed dynamics depend critically on the altitude of energy deposition, strongly determined by the (unknown) spectral energy distribution (e.g., Sojka et al 2013). Our physically modeled DEMs allow generation of synthetic X-ray spectra in this unobserved passband, filling a crucial gap in the needed input for modeling of upper atmospheric behavior.…”

Attribution of interminima changes in the global thermosphere and ionosphere

“…Furthermore, Liu et al . [] found no interminima change in daytime electron densities at the E region peak ( N m E ), which is seemingly inconsistent with an interminima EUV irradiance decrease, since N m E responds positively to EUV, as well as to soft X‐rays [e.g., Sojka et al ., ]. Jee et al .…”

“…Araujo-Pradere et al [2011] reported interminima TEC decreases above four GPS receiver stations but found no systematic interminima N m F 2 change among four ionosonde stations. Furthermore, Liu et al [2011] found no interminima change in daytime electron densities at the E region peak (N m E), which is seemingly inconsistent with an interminima EUV irradiance decrease, since N m E responds positively to EUV, as well as to soft X-rays [e.g., Sojka et al, 2013]. Jee et al [2014] reported daytime interminima decreases in altimeter-derived, over-ocean TEC data, as well as offsetting nighttime increases that resulted in no net global change.…”