Abstract
The 22 July 2009 solar eclipse with an obscuration of > 83% at Chung-Li (24.9°N, 121.2°E, Dip 35°N) in Taiwan during noon hours has provided a unique opportunity for us to examine its impact on E-region irregularities which were observed simultaneously by the 52 MHz coherent radar and a co-located ionosonde. Significant observations revealed that the daytime E-region strong backscatter echoes at multiple heights and a sudden intensification of the weak sporadic E-layer during the 22 July 2009 solar eclipse. These results follow the research findings of Patra et al. (2009). As the incident solar radiation suddenly blocked by intruding Moon during solar eclipse events that would generally create night-like ionospheric conditions, it is surmised that the E-region irregularities were indeed induced by the eclipse associated effects. The induced effects resulted in faster recombination of molecular ions, generation of gravity waves and electric fields that could have created a conducive environment to excite plasma irregularities through a gradient-drift instability mechanism. The vertical shears of radar Doppler velocity and the peak radar backscatter at the node of Doppler velocity shear, as resolved by the coherent scatter radar with interferometer technique, were possibly due to the upward propagating gravity waves and wave-induced polarization electric fields. The present observational results should not only be highly useful to ascertain plausible mechanisms responsible for nighttime E-region irregularities, but also provided evidence that a solar eclipse could generate E-region plasma irregularities over temperate mid-latitudes for the first time.
Highlights
Observing a solar eclipse provides a unique opportunity to study various atmospheric processes as it temporarily cuts off solar radiation which is responsible for almost all the physical mechanisms occurring within the Earth’s atmosphere
Away from equatorial regions, Patra et al (2009) and Thampi et al (2010) used VHF radars located at Gadanki (13.5°N, 79.2°E, Dip 12.5°N), a low-latitude station in India, and at Shigaraki (35.85°N, 136.1°E, Dip 48°N), a mid-latitude station in Japan, to investigate local E-region responses to solar eclipses; both stations have observed E-region plasma density irregularities during partial solar eclipses which occurred on 11 August 1999 and 22 July 2009, respectively
It would be most interesting to investigate whether daytime E-region irregularities are observed during the longest solar eclipse which occurred on 22 July 2009 over a typical equatorial ionization anomaly crest zone station such as Chung-Li (Geographic Lat. 24.9°N, Geographic Long. 121.2°E, Dip 35°N) which is located at temperate mid-latitudes exactly in between the Gadanki and Shigaraki latitudes and where the nighttime backscatter echoes using the 52 MHz radar have been long reported (Chu et al 1996; Chu and Wang 1997)
Summary
Observing a solar eclipse provides a unique opportunity to study various atmospheric processes as it temporarily cuts off solar radiation which is responsible for almost all the physical mechanisms occurring within the Earth’s atmosphere. Away from equatorial regions, Patra et al (2009) and Thampi et al (2010) used VHF radars located at Gadanki (13.5°N, 79.2°E, Dip 12.5°N), a low-latitude station in India, and at Shigaraki (35.85°N, 136.1°E, Dip 48°N), a mid-latitude station in Japan, to investigate local E-region responses to solar eclipses; both stations have observed E-region plasma density irregularities during partial solar eclipses which occurred on 11 August 1999 and 22 July 2009, respectively. Both Patra et al (2009) and Thampi et al (2010) hypothesized that a solar eclipse could provide ‘night-like’ conditions which allow the excitation of plasma instability and the generation of plasma irregularities.
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