2011 SuperDARN Workshop       

SuperDARN observation of March 9, 2011 X-class solar flare

S.G. Shepherd and E.D.P. Cousins
Thayer School of Engineering, Dartmouth College, Hanover, NH USA

abstract. Enhanced x-ray flux resulting from an X-1 class solar flare on March 9, 2011 had a rapid and dramatic effect on the Earth's ionosphere that was observed by many of the SuperDARN radars. The x-ray flux, recorded by the GOES spacecraft, caused a rapid increase in ionization which, in turn, was seen by many of the SuperDARN radars as a positive (toward the radars) Doppler velocity on all beams, combined with a reduction in backscattered power, and a slower recovery to quiescent conditions. Although seen mostly in Doppler spectra from ground or sea scatter the effects were also seen in Doppler measurements from ionospheric scatter. Observations show enhanced ionization causing D-region absorption of HF transmissions during the most intense period of x-ray flux and recovery beginning shortly after the x-ray-induced ionization begins declining from its maximum level. The observed effects are mostly consistent with expectations, with the radars closest to the sub-solar point recording the strongest response and radars located on the night-side, where they are shielded from the impinging x-rays, seeing little to no response. There are, however, differences from the expected behavior and SuperDARN appears to be well-suited to contribute to a better understanding of the complicated ionospheric response to x-ray events.

Sakaguchi KaoriNICT Japan