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- Title
A Modeling Framework for Estimating Ionospheric HF Absorption Produced by Solar Flares.
- Authors
Chakraborty, S.; Baker, J. B. H.; Fiori, R. A. D.; Ruohoniemi, J. M.; Zawdie, K. A.
- Abstract
Over‐the‐Horizon communication is strongly dependent on the state of the ionosphere, which is susceptible to solar flares. Trans‐ionospheric high frequency (HF, 3–30 MHz) signals can experience strong attenuation following a solar flare that lasts typically for an hour, commonly referred to as shortwave fadeout (SWF). In this study, we examine the role of dispersion relation and collision frequency formulations on the estimation of SWF in riometer observations using a new physics‐based model framework. The new framework first uses modified solar irradiance models incorporating high‐resolution solar flux data from the GOES satellite X‐ray sensors as input to compute the enhanced ionization produced during a flare event. The framework then uses different dispersion relation and collision frequency formulations to estimate the enhanced HF absorption. The modeled HF absorption is compared with riometer data to determine which formulation best reproduces the observations. We find the Appleton‐Hartree dispersion relation in combination with the averaged collision frequency profile reproduces riometer observations with an average skill score of 0.4, representing 40% better forecast ability than the existing D‐region Absorption Prediction model. Our modeling results also indicate that electron temperature plays an important role in controlling HF absorption. We suggest that adoption of the Appleton‐Hartree dispersion relation in combination with the averaged collision frequency be considered for improved forecasting of ionospheric absorption following solar flares. Plain Language Summary: Sudden bursts of electromagnetic radiation from the Sun, also known as solar flares, alter the physical properties of the ionosphere. The sudden enhancement in incoming solar radiation affects over‐the‐horizon radio communication channels on the dayside of the Earth, commonly known as shortwave fadeout (SWF). This study describes a new approach for estimating ionospheric radio wave absorption, using different formulations of wave dispersion relation and collision frequency and compares their relative merits using direct observations of absorption in the ionosphere. We examine how different physical parameters, such as the location of the transmitter, intensity of the solar flare, ionospheric composition, and background conditions, such as electron temperature impact SWF. Key Points: A new high frequency (HF) absorption model reproduces observations more accurately than the existing D‐region Absorption Prediction model with an average skill score of 40%Incorporating a broad range of solar irradiance wavebands and plasma‐neutral interactions can significantly improve HF absorption predictionModel results suggest changes in the D‐region electron temperature can impact the HF absorption experienced by traveling radio waves
- Subjects
OVER-the-horizon radar; REMOTE sensing by radar; IONOSPHERE; ATMOSPHERIC physics; SHORTWAVE radio
- Publication
Radio Science, 2021, Vol 56, Issue 10, p1
- ISSN
0048-6604
- Publication type
Article
- DOI
10.1029/2021RS007285