A well observed and unusually oriented flare

Science nugget: Nov 28, 1997

Data of the X-class flare on Thanksgiving Day were downlinked at Wallops, and were already copied to the ISAS archive about 12 hours later. Without delay we reformatted the data. The flare was very well observed by Yohkoh. It occurred in AR 8113. First, the Sun about 20 minutes before the flare onset is shown. The boxes show the FOV of quarter and half resolution images of SXT. They correspond to 5.2 arcmin and 10.4 arcmin. High cadence images, in full resolution, are taken in the 2.6 arcmin FOV. (Click on the picture to see a larger, more visible,version.)

The HXT channels are 14-23 keV, 23-33 keV, 33-53 keV, 53-99 keV. Unlike the X9 flare of 6-NOV-97, no serious saturation is seen in the HXT data.
Next, time sequence SXT images are shown. These are half resolution (2x2 summation, 5.2 arcmin FOV) images. The central part is substituted by less severely saturated full resolution images Also, HXT L-band (14-23 keV) images are superimposed. As far as these SXT images are concerned, ejections are seen in the southeast direction. Look at the image of 13:13:12. Emission was already growing just to the left of the inset. It seems detached from the bright area in the next frame, moving out of the FOV at 13:15:58, leaving some loop structures behind. A similar pattern is seen again in the last frame, but the direction is slightly different. (Click on the picture to see a larger, more visible, version.)

A more complete view of the plasma ejection is given in a movie of 10.4 arcmin FOV images. The ejection first goes in the southeast direction, then turns to north east, probably following some field lines. Incidentally, the ejection seems to be repeated

mpg movie here.
Lastly, we roughly described the motion of the plasma ejection. As the movie (see above) shows clearly, it really does not look much like your classic "plasmoid" rising vertically; the projected motion is roughly perpendicular to the projection of the local vertical, and it does not look like a twisted flux rope. The figure below shows the locations of position measurements from the quarter resolution data (10' FOV); these were arbitrarily taken along one of the support shadow rays for concreteness.

(Click on the graph to see a larger, more visible, version.)

The resulting distance-vs-time plot is shown below, superposed on the HXT M2 (33-53 keV) light curve on a linear scale. The zero reference for distances is the brightest point in the post-impulsive phase, taken to be the top of a compact loop or arcade. The slope corresponds to 330 km/sec; sorry the distance scale is not shown (the Y axis is labeled with the HXT count number).

(Click on the graph to see a larger, more visible, version.)

Further analysis of this and other flares continues.

Nariaki Nitta 28-Nov-97 (email nitta@isass0.solar.isas.ac.jp)