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Examining the Role of Dispersion Relation and Collision Frequency Formulations on Estimation of Shortwave--Fadeout
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  • Shibaji Chakraborty,
  • Joseph Baker,
  • John Michael Ruohoniemi,
  • Kate Zawdie,
  • Robyn Fiori,
  • Nozomu Nishitani
Shibaji Chakraborty
Virginia Tech

Corresponding Author:[email protected]

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Joseph Baker
Virginia Tech
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John Michael Ruohoniemi
Virginia Tech
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Kate Zawdie
US Naval Research Laboratory
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Robyn Fiori
Natural Resources Canada
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Nozomu Nishitani
Institute for the Space-Earth Environmental Resaerch
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Over–the–Horizon (OTH) communication is strongly dependent on the state of the ionosphere, which is susceptible to solar flares. Trans–ionospheric high frequency (HF) signals experience a strong attenuation following a solar flare, commonly referred to as Short–Wave Fadeout (SWF). In this study, we examine the role of dispersion relation–collision frequency formulations on the estimation of flare–driven HF absorption seen in Riometer observation using a data assimilation framework. Specifically, the framework first uses modified solar irradiance models (such as EUVAC, FISM), which incorporate high–resolution solar flux data from GOES satellite X-ray sensors, to compute the enhanced ionization produced during the flare events. The framework then uses different dispersion relation–collision frequency formulations to estimate enhanced HF absorption. Finally, the modeled HF absorption is compared against the data to determine which combination of dispersion relation–collision frequency formulation best reproduces the Riometer observations. From the modeling work, we find that the Appleton–Hartree dispersion relation in combination with Schunk–Nagy collision frequency profile produces the best agreement with Riometer data.