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<p>The present study investigates the cause of oscillation in the critical frequency (foF2) and peak height (hmF2) of the F2 layer during evening hours in the low solar activity year 2020 using 5-min resolution ionogram data from the midlatitude stations Nicosia (35.025°N, 33.157°E) and Athens (38.0°N, 23.5°E). Analysis of geomagnetically quiet days reveals that the normalized fluctuations in foF2 and hmF2 exhibit oscillations with periodicities ranging from 120 to 240&#xa0;min, which are associated with large-scale atmospheric gravity waves (AGWs)/traveling ionospheric disturbances. Observations reveal two distinct types of wave-induced oscillations in foF2 and hmF2: one that begins in the afternoon, intensifies after sunset, and fades before midnight; and another that initiates shortly after sunset and similarly weakens before midnight. Analysis of the events indicates westward-propagating acoustic-gravity waves (AGWs), with estimated propagation velocities ranging from 439 to 615 m/s for afternoon AGWs and 256 to 341&#xa0;m/s for solar terminator AGWs.</p>

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Signature of large scale gravity waves in foF2 and hmF2 observed at midlatitude stations during geomagnetically quiet days

  • 期刊论文

  • 发表日期：

    2025年7月23日

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  • N. Ankitha,
  • Asha Anie Varghese,
  • Blessy Varghese,
  • Gopika S. Vijayan,
  • Abraham Abraham,
  • Rekha Unni,
  • Tiju Joseph Mathew

摘要

The present study investigates the cause of oscillation in the critical frequency (foF2) and peak height (hmF2) of the F2 layer during evening hours in the low solar activity year 2020 using 5-min resolution ionogram data from the midlatitude stations Nicosia (35.025°N, 33.157°E) and Athens (38.0°N, 23.5°E). Analysis of geomagnetically quiet days reveals that the normalized fluctuations in foF2 and hmF2 exhibit oscillations with periodicities ranging from 120 to 240 min, which are associated with large-scale atmospheric gravity waves (AGWs)/traveling ionospheric disturbances. Observations reveal two distinct types of wave-induced oscillations in foF2 and hmF2: one that begins in the afternoon, intensifies after sunset, and fades before midnight; and another that initiates shortly after sunset and similarly weakens before midnight. Analysis of the events indicates westward-propagating acoustic-gravity waves (AGWs), with estimated propagation velocities ranging from 439 to 615 m/s for afternoon AGWs and 256 to 341 m/s for solar terminator AGWs.