Abstract
The Wuhan Ionospheric Oblique Backscatter Sounding System (WIOBSS) was applied as a bistatic radar to record the ionospheric E-region responses to a solar eclipse on 22 July 2009. The transmitter was located in Wuhan and the receiver was located in Huaian. The receiver observed anomalous echoes with larger Doppler shifts at the farther ranges compared with the echoes reflected by Es. According to the simulated ray propagation paths of the reflected and scattered waves, we considered that the anomalous echoes were scattered by E-region field-aligned irregularities (FAIs). The locations of the FAIs recorded by the WIOBSS were estimated with the International Geomagnetic Reference Field (IGRF) and the observed propagation parameters. These irregularities occurred at around the eclipse maximum and lasted for ~20–40 min. The steep plasma density gradient induced by the fast drop photo ionization under the lunar shadow was beneficial to the occurrence of gradient drift instability to generate the FAIs. They were different from the gravity wave-induced irregularities occurring in the recovery phase of the solar eclipse.
Highlights
Academic Editor: When the moon moves between the sun and the Earth, the extreme ultraviolet (EUV) radiation of the sun is completely/partially blocked by the moon, resulting in a total/annular or partial solar eclipse
The Chung-Li radar observed two patches of the field-aligned irregularities (FAIs); one patch appeared at the eclipse maximum with a remarkable Es peak frequency enhancement and the following irregularities occurred with a much higher signal-to-noise ratio (SNR)
The enhanced echo power as well as the newly emerging four- and five-hop waves recorded by the Huaian and Suzhou receivers showed that more waves were scattered due to the steeper plasma density gradient forming during the solar eclipse [23]
Summary
Academic Editor: When the moon moves between the sun and the Earth, the extreme ultraviolet (EUV) radiation of the sun is completely/partially blocked by the moon, resulting in a total/annular or partial solar eclipse. It is a rare astronomical phenomenon and the rapid solar radiation variations produced by a solar eclipse can bring an unusual influence on the atmosphere and ionosphere of the Earth [1,2,3]. There are few reports about solar eclipse-associated E-region FAIs. Whilst reviewing the observation data of the eclipse day of 22 July 2009, we found anomalous echoes on the Wuhan–Huaian link recorded by the Wuhan Ionospheric Oblique. A traditional monostatic radio system receives backscattering echoes to observe FAIs; a bistatic radio.
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