Disturbances in Sporadic-E During the Great Solar Eclipse of August 21, 2017

The great solar eclipse traveled eastward through the American Continent from coast to coast on August 21, 2017 and provided a rare opportunity to investigate the ionospheric responses to the rapid solar radiation variations. We have analyzed the peak electron density and density gradient variations in Sporadic E (Es) and applied the data of four Digisondes close to the eclipse path. All the four Digisondes have recorded the same interesting phenomena. One is the depletion on the fbEs (blanketing frequency of Es layer) curve during the solar eclipse and the other is the enhancements on the semi-transparency parameter of Es layer Delta f after the solar eclipse, where Delta f = ftEs-fbEs, and ftEs is the top frequency of Es layer. The wind disturbances on the tidal wind and the photoionization decrease during the eclipse are put forward as a possible reason for the peak plasma density reduce. The periodic gravity waves have been observed in both ionospheric E and F region. However, the Delta f enhancements occurred after the gravity waves had passed through the Es layer. Thus, we suggest that the solar induced waves did not raise the plasma density gradient directly. Gravity waves breaking may occur in the Mesosphere/Lower Thermosphere region to deposit momentum and produce turbulence, and so the accompanying instabilities may be generated to enhance the electron density gradient in E-region.

Automated summary

The great solar eclipse on August 21, 2017 provided a rare opportunity to investigate the ionospheric responses to rapid solar radiation variations. Analysis of peak electron density and density gradient variations in the Es layer during the eclipse suggested possible reasons for the peak plasma density reduce, including wind disturbances and photoionization decrease. Observations of periodic gravity waves in the ionospheric E and F region indicated that solar induced waves did not directly raise the plasma density gradient.