SXT REPORT FOR WEEK 13: 21 MARCH 1993 - 28 MARCH 1993 GENERAL STATUS SXT continues to function well after passing its one-millionth-image milestone. In fact, SXT has taken a total of 1,008,855 images (165,784 full frame and 843,071 partial frames). We have had some SEU problems but they have been recovered quickly by the KSC tobans. The Sun has been moderately active over the last week, producing 2 M flares and at least 43 C flares. The GOES background level started the week at around the C1 level but dropped to about B4 by the end of the week. Japan is particularly beautiful at the moment with the Magnolia trees in full flower and the famous cherry blossoms starting to show. The "Yohkoh Flares" came in second in a game of yakyu (baseball) to a team of graduate students from the University of Tokyo. This was a good result for the "Flares" as we nearly came in third but managed to force extra innings by a late-innings rally. The final score was 13-12, which, astronomically and statistically speaking, is a draw. There are a lot of aching astronomers around here today. PERSONNEL Gary Lindford and Marilyn Bruner arrived at ISAS this week bringing the Lockheed team back up to full strength. Gary is back for his final month of operations and will be here until mid April. Marilyn will be at ISAS for about 3 months and is learning the job of chief observer from Keith Strong. Richard Shwartz is here from GSFC for a month and Lidia van Driel-Gesztelyi is visiting for a couple of weeks. Bachtiar Anwar has just successfully completed his Ph.D. on SXT data and is returning soon to Indonesia. We wish him well. George Simnett left at the beginning of the week. SOLAR ACTIVITY Although we observed some good flares, the most interesting events have been associated with large scale coronal evolution. The return of the longitudes that produced the huge helmet streamer associated with a polar crown filament eruption last rotation was not disappointing. The phenomenon was repeated on 23 March 93 but we were looking down on it this time instead of from the side. We suspect the polar crown filament reformed and then was destabalized again. Comparison of these two events should producing some fascinating insights to the evolution and structure of such events. There were some spectacular, large-scale, dynamic loops visible off the S.E. limb earlier on 21 March 93 between 14:05 and 20:40 UT. They were initially seen as a large (~140,000 km) of broad, diffuse loops. These slowly faded as they expanded and within 5 hours had almost entirely disappeared, however in the next 40 minutes they reappeared as a fine web of loops in response to a new stimulus from a nearby active region. These should provide good examples for loop cooling and scale height studies. An active region coming over the northeast limb showed the now classic behavior of a small, leading bipole interacting with the region and surrounding quiet Sun. A thin jet was reported by the tobons that lasted for over 30 minutes on 22 March 93 at 16:04 UT. SCIENCE PROGRESS Watanabe-san reported that he has collected most of the papers from the February Science meeting near ISAS and is ready to get them printed. Richard Schwartz has been helping several of us to access relevant GRO data and compare it to Yohkoh data. There seems to be some exciting possibilities in this area because of GRO's significantly higher sensitivity combined with he imaging capabilities of Yohkoh. Keith Strong has been evaluating some of the Gamma-ray flares jointly observed by Yohkoh and GRO in October 1991. Unfortunately, Yohkoh had not yet started full DSN coverage and the coverage in most events is very poor. We must await the next large burst of gamma-ray flares to get comprehensive joint data. Hugh Hudson has been putting the final touches to a paper to be submitted to Nature about the thermal bursts observed at loop footpoints during the impulsive phase of flares. In developing this paper there appears to be a wealth of details that only a longer and more detailed paper can describe so we are starting to plan that project while completing this one. These observations seems to be linked to the discovery of the large, early blue shifts seen in the BCS data for some flares. George Simnett, George Doschek, Len Culhane, and Keith Strong are looking at a series of Yohkoh flares which have good GRO coverage during the impulsive phase, show large BCS blue shifts, and occurred at a time when the Sun had few other regions on the disk so we can look very early and see exactly when the plasma dynamics were first visible. Hugh Hudson and Lidia van Driel-Gesztelyi have been surveying large flares observed by Yohkoh and found that all X flares are clearly white-light flares too. This detailed study has only been made possible by the new alignment software from Jean-Pierre Weulser and Tom Metcalf. Marilyn Bruner is planning on analyzing the SXT data that was taken in conjunction with her SPDE rocket flight. SXT OPERATIONS SXT suffered from three SEU errors this week (19 March Pass 2, 24 March Pass 4, and 25 March pass 1). The Mainframe 1 computer was down several times early in the week, sometimes during operations. This resulted in the SXT tables not being properly archived. An error was made in the table load by updating the wrong table because the archive was out of phase. The net result, because, fortunately, the new table and archived table were almost identical, was to load additional changes to the table that were unnecessary. We have been making preparations to make joint observations with the NIXT rocket. Nariaki Nitta has been supplying SXT images to the NIXT team for planning. A meeting has been called for Wednesday 31 March to plan Yohkoh operations modes and the corresponding SXT tables. Keith Strong, 28-Mar-1993