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Ionospheric Sluggishness: A Characteristic Time-Lag of the Ionospheric Response to Solar Flares
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  • Shibaji Chakraborty,
  • John Michael Ruohoniemi,
  • Joseph Baker,
  • Scott Bailey,
  • Robyn Fiori,
  • Kate Zawdie
Shibaji Chakraborty
Virginia Tech

Corresponding Author:[email protected]

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John Michael Ruohoniemi
Virginia Tech
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Joseph Baker
Virginia Tech
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Scott Bailey
Virginia Polytechnic Institute and State University
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Robyn Fiori
Natural Resources Canada
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Kate Zawdie
US Naval Research Laboratory
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The term “ionospheric sluggishness” is used to describe the time delay between maximum radio absorption in the ionosphere following the time of maximum irradiance during a solar flare. Sluggishness is one of the characteristic properties known to be maximized around D-region heights and can be used for studying lower ionospheric (D-region) and mesospheric chemistry. This article is our first attempt to estimate ionospheric sluggishness using high frequency (HF, 3 – 30 MHz) instruments. Specifically, we report on first estimates of sluggishness from riometer and SuperDARN observations following a solar flare and propose two new methods to estimate sluggishness. Sluggishness is shown to be anti-correlated with the peak solar X-ray flux and positively correlated with solar zenith angle and geographic latitude. The choice of instrument, method, and reference solar waveband effects the sluggishness estimation. A simulation study was performed to estimate the effective recombination coefficient, which was found to vary between 4-5 orders of magnitude. We suggest that the effective recombination coefficient is highly sensitive to D-region’s negative and positive ion chemistry.
Apr 2021Published in Journal of Geophysical Research: Space Physics volume 126 issue 4. 10.1029/2020JA028813