Effect of solar soft X-rays on the lower ionosphere



New measurements of solar irradiance in the soft X-ray region of the spectrum from the SNOE satellite [Bailey et al., 2000] show that the full-disk solar irradiance in the ∼2–20 nm region is higher than a standard model [ Hinteregger et al., 1981] by a factor of ∼4 at all levels of solar activity. This confirms contentions developed from several lines of evidence, [e.g., Richards and Torr, 1984; Richards et al., 1994] but to a larger degree than previously suspected. This finding has many implications for the thermosphere and ionosphere, two of which are examined here. Greatly improved agreement between measurement and model of the photoelectron spectrum is obtained when the solar soft X-ray input is adjusted to the SNOE measurements. We also found good agreement between electron density profiles measured by the incoherent scatter radar at Millstone Hill [ Buonsanto et al., 1992] and our model, solving a fundamental problem identified in that work.