Solar Physics Division Meeting 2000, June 19-22
Session 14. Flares and Transients
Oral, Chair: P. L. Bornmann, Thursday, June 22, 2000, 11:00am-12:00noon, 1:30-2:30pm, Forum

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[14.06] High Cadence Flare Observations

H. Wang, J. Qiu, C. Denker, T. Spirock, H. Chen, P.R. Goode (BBSO)

We analyzed high cadence observations of a C5.7 flare of 1999 August 23 at Big Bear Solar Observatory (BBSO). The observing wavelength was 1.3~Å\ in the blue wing of H\alpha line. The observations were made with a 12-bit SMD camera with a cadence of 33~ms and an image scale of 0.3\arcsec\ pixel-1. In addition, the time profile of hard X-rays obtained by BATSE (with the cadence of 1.024~s) and BBSO high resolution magnetograms are compared with H\alpha observations to understand detailed particle precipitations of this event. The important results are:

(1) In H\alpha-1.3~Å, three flare kernels were observed in the early phase of the flare. The flare started in a non-magnetic area at the magnetic neutral line. We may have detected the top of a low-lying loop which was the initial energy release site. While the other two kernels may be the footpoints of another overlying flare loop formed after the magnetic reconnection.

(2) We analyzed the temporal behavior of the three flare kernels in the impulsive phase when hard X-ray emission was significant. We found that during a 7~s period, the H\alpha-1.3Å~ brightenings at one of the footpoints showed very good temporal correlation with the hard X-ray flux variation. Therefore, from the spatially resolved H\alpha offband observations, we identified this flare kernel as the source of hard X-ray emission.

(3) From the footpoint which exhibited best correlation with the HXR, the H\alpha-1.3Å~ emission showed high frequency fluctuation in a time scale of a few tenths of a second. The amplitude of the fluctuation was more than three times above the noise. Such fluctuation was not evident in other flare kernels which did not show good correlation with the hard X-ray emission. Therefore, the observed high frequency fluctuation might be the real signature of fine temporal structure related to the HXR elementary bursts.

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