A wonderful X-class flare for RHESSI
Since RHESSI was launched on February 5, 2002, the Sun had steadfastly refused to commit to an X-class flare. This provided the RHESSI team with further (irritating) evidence that the occurrence of the biggest flares follows different statistical laws than apply to smaller ones; there had been some 40 M-class events during the first ten weeks of RHESSI operations. According to what we know about the statistics of flare occurrence, this should have corresponded to the occurrence of half-a-dozen X-class events. But, in the end there was a spectacular reward:
Fans of Yohkoh science nuggets will recognize the pattern in the TRACE image above. See for example  or  for comparable events as observed by Yohkoh. Such events (a) have spiny fans above their coronal arcades, in which (b) downward coronal flows persist; they (c) have unusual hard X-ray properties. All in all they are wonderful and are surely telling us some important things about the coronal restructurings that we study as flares or coronal mass ejections.
This flare will be the subject of many studies, and certainly the RHESSI data are far from a comprehensive analysis because it's all so new, but in this nugget we can show a few of the hot items flashing around the Web within the past week. Below are RHESSI light curves (highly preliminary and full of artifacts) plus a seldom-seen SRBL dynamic microwave spectrum:
Essentially the upper plot shows hard X-ray time profiles during the rise phase of the event; the lower plot shows the microwave spectrum over the whole interval. The plots are not coaligned well, but one can click on each image for a better view., For people actually interested in the artifacts and circumstances, see here.
Finally, some movies from TRACE, in two sizes (large, 350 kB; and huge, 1.2 MB):
The movies show most exquisitely the SAD ("Supra-Arcade Downflow") that the Yohkoh nuggets linked above mentioned; one immediate important question for these beautiful TRACE data is the temperature structure; RHESSI will be decisive here where Yohkoh could not.
April 26, 2002H. Hudson (firstname.lastname@example.org), with thanks to Eduard Kontar, David McKenzie, Jun Sato, and Harry Warren.