Responses of the D region ionosphere to solar flares revealed by MF radar measurements

• Published in: Journal of atmospheric and solar-terrestrial physics 2019-01, Vol.182, p.211-216
• Main Authors: Li, Na, Lei, Jiuhou, Luan, Xiaoli, Chen, Jinsong, Zhong, Jiahao, Wu, Qian, Xu, Zhengwen, Lin, Leke
• Format: Article
• Language: English
• Subjects: Electron density; MF radar; Reflection height; Solar flare
• ISSN: 1364-6826; 1879-1824
• DOI: 10.1016/j.jastp.2018.11.014

Electron density (Ne) and effective reflection height (H', where the electron density reaches its peak value) in the D region observed by medium frequency (MF) radar at Kunming (25.6°N, 103.8°E) were utilized to quantitatively study the ionospheric response to solar flares. It was found that the H' and Ne had profound responses to solar flares. The results showed a sharp decrease in the H' from 76 to 80 km during the non-flare period to nearly 58 km with flares, and a sudden increase in the Ne from below 4×108 m3 in non-flare period to 1.8×109 m3 during 13 M-level flares. The behavior of Ne was strongly and positively correlated with the variation of the X-ray flux, with the largest coefficient being 0.93, while the changes of H' exhibited a strongly negative correlation of −0.96 with that of the X-ray flux. Moreover, variations of H' and ΔNe depended on not only the flare level, but also upon the onset time and duration of flare. •Ne and H' from MF radar are used to quantify the ionospheric D region response to solar flares.•During solar flare periods, the H' delines rapidly from near 76 km–58 km, and ΔNe is greater than 8×108 m3, up to 1.7×109 m3.•Ionospheric response to solar flares depends on the level, onset and duration of the solar flare.