SXT REPORT FOR WEEKS 8 & 9: 14-27 February 1993 =============================================== General Status -------------- This is a report covering the last fortnight as preparations for the Yohkoh science meeting absorbed so much of the operation's team time. SXT has had a couple of SEU errors which were recovered from quickly, but as the BCS has had similar problems I suspect it to be due to the phasing of the apogee of the Yohkoh orbit with the SAA. The errors, which are much less frequent than this time last year thanks to modifcation of the onboard software, are under investigation. The Sun was initially quite active but has quieted down significantly in the last three days; over the reporting period it has produced at least 7 M-class flares and about 50 C-flares. SXT has now taken over 942,000 images (~156,000 full-frame and 786,000 partial-frame images). Personnel --------- There has been a huge influx of people at ISAS for the science meeting held at a nearby conference center (see details below). Many of the 100 scientists that attended visited ISAS either before or after the meeting. Several are staying on for extended visits (Bob Bentley, Uri Feldman, George Doschek, George Simnett, etc.). Karen Harvey, Greg Slater, Nariaki Nitta, and Hugh Hudson are leaving next week for varying lengths of time. This will leave the operations team short handed for a while. We had a seminar by given by Karen Harvey entitled "The Role of Magnetic Flux Cancellation in XBPs". It detailed some of the work she has been doing with comparisons of Yohkoh data with Kitt Peak magnetograms and He 10830. There was lots of interested dialogue, particularly associated with an XBP flare and associated X-ray jet. She presented a scenario that corresponded very closely to that Shibata-san had independently arrived at in studying jets involving reconnection. Solar Activitiy and Interesting Events -------------------------------------- Many of the flare events were observed by Yohkoh but complete data will have to await reformating. However from just looking at the data collected at the KSC passes showed an interesting transition from an active Sun to a very much quieter configuration. The active regions have all seemed to be simple bipoles but we have noted that some have been reverse polarity, in fact an unusually high proportion. Another feature that these active regions have shared is a small XBP leading the leader spot. these have tended to be very active, often flaring and producing jets. One region produced a repeat of the 7 Dec 1991 flare/jet that Karen Harvey discussed in detail in her talk. Some of the velocities are in excess of 500 km/s and approach 1000 km/s in a few cases. Speaking of repeats one of the most exciting events occured when the solar activity had dropped to about B3 on GOES. There was an identical event to that of 24 Jan 92 (the poster helmet). This time however we seem to have better data coverage (half-resolution data, deeper exposures, and good ground based coverage). It coincided with the visit to ISAS of Jim Klimchuk and Dave Sime, so it has caused much excitment. So far the structure has survived 3 days, growing and expanding slowly. While there is wildly different interpretations of these events, Jim Klimchuck, Dave Sime, Karen Harvey and Keith Strong has agreed to work on this event together. Hopefully others interested in this problem will join as well. Sciences Progress ---------------- We have just finished the 3-day Yohkoh science meeting. There were many exciting results, many of them were far more quantitative than before showing a great deal of scientific progress. There were constructive and lively interchanges between the >100 participants from all over the world. Professor Uchida, Professor Ogawara, and Dr. Shibata should be congratulated for putting such an effective programme together. It was a lot of hard work on their part but worth in the eyes of the participants. The Lockheed team did very well. Greg Slater gave a great quantitative presentation on the scatter pattern seen in overexposed flare images. Gary Linford did well discussing temperatures of a small flare, the session chair had to call a halt to the deluge of questions. Karen Harvey gave a great talk on XBP's based on the 9/10 Dec 92 XBP run, again lots of debate. Nariaki Nitta won the most entertaining talk award given by Sakurai-san by somehow (sucessfully) linking AR flaring with bloodtype analysis. Actually it was one of the best attempts that I have seen to link the analysis of long-term active-region development to flaring in a sound statistical manner. Keith Strong presented a somewhat contriversal talk on the bright footpoints seen in the earliest phases of flares. There were several impressive presentations by the Hawaii group. One result, presented by Tom Metcalf, detailed the surprising result the active-region heating seems unrelated to large-scale currents. A truely excellent paper was presented by Hara-san on the temperature of coronal holes. He had very methodically analysed some SXT images of coronal holes, finding temperatures of about 2 MK. Still the most confounding result from the SXT data is the confined bright emission at the tops of loops that was presented by Uri Feldman. The length of time that the brightness gradient is maintained is longer than seems plausible for just about any conceivable physical mechanism. Several interesting results were also presented by the other Yohkoh experiments. The BCS team showed data from a survey of many bright flares which show a surprisingly low value for the average upflow rates in flares. The WBS team showed some gamma-ray spectra from the 4 big flares that they have observed so far. HXT images are begining to be used as commonly as SXT images in flares analysis now. The most pleasing aspect of the meeting was the way in which the data from different Yohkoh instrumentation and ground-based observatories is beginning to be analysed as a whole rather than by an individual event or instrument basis. This is a direct result of the holistic approach adopted for the Yohkoh software. SXT Operations -------------- With many of the Hawaii and Lockheed pointing experts here for the meeting we held a discussion of the problem of "de-jittering" SXT images. Jean-Pierre Wuelser demonstrated some new software that used HXA data to correct IRU data for x-ray image coalignment. It worked impressively. Greg Slater has managed to make a direct optical disk to optical disk copy here at ISAS. Astro-D, now know as ASCA, was launched successfully launched on 20 February. The short delay in the launch was very advantagous to Yohkoh as it means there is almost no interference with Yohkoh operations. The two spacecraft will slowly move into phase with each other over the next year when we stand to loose about half of our KSC and DSN passes. Keith Strong, 28-Feb-1993