SXT Status Report March 8 through March 21, 1999 (Weeks 11-12) H. Hudson SUMMARY Solar activity rose to a higher level during these two weeks. There were no technical difficulties with SXT, and we conducted some joint observations with TRACE and SOHO. A NASA press release on "S marks the spot" (sigmoids leading to CMEs) produced a great deal of publicity. SOLAR ACTIVITY There were eleven M-class events at the time of writing, dominated by AR8485 and 8487. The AR8485 spot group reached 610 millionths in area on the 17th. The disappearance of these regions then caused a precipitous drop in GOES flux level on the 19th. Choosing between the two competing regions was the tricky part of the coordinated observations during week 11! The NS interconnecting loops that had been so remarkable one rotation ago, in fact did not reappear as half expected. So it may be that the trans-equatorial loop visibility comes and goes with the active regions, in spite of the strong tendency for these structures not to link the core fields of these regions. Perhaps... this might be a good subject for a future science nugget. OBSERVING CAMPAIGNS SXT co-observed briefly with TRACE and SOHO (CDS) in an attempt to observe preflare signatures (N. Ranns, MSSL). Between 8485 and 8487 there was plenty of activity, but as is well-known, preflare signatures have been shown by earlier Yohkoh studies to be perplexing in their capriciousness and possible irrelevance. But theoretically, this should not be the case. Perhaps the sigmoids are telling us something different about preflare arrangements for flares. SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES A small stray-light jump took place on March 12, as noted in the "quick function survey" Web pages by four people, and this might mean an additional change in the SXT aperture filter. However it coincided closely with a re-definition of the Yohkoh pointing, so the change might have resulted from this reconfiguration instead. The Chief Observer has an action item to research this in a bit more detail, encouraged in this by Acton, who is in the process of tying up the loose ends of this instrument behavior. Perhaps in an earlier status report we commented that he is no longer quite so sure about the micrometeoroid theory. SXT OBSERVING SEQUENCE TABLES ----------------------------------------------------------------- JST Day UT Time Pass Table ID ================================================================= 8-MAR-99 2 990307 P2 ARS1 STD (*) 8-MAR-99 1 990308 P1 ARS2 STD 9-MAR-99 5 990308 P5 ARS2 DRK (*) 10-MAR-99 2 990309 P2 ARS2 DIF (*) 11-MAR-99 2 990310 P2 ARS2 STD (*) 12-MAR-99 2 990311 P2 ARS2 STD (*) 13-MAR-99 3 990312 P3 ARS1 STD (*) 14-MAR-99 2 990313 P2 ARS1 STD 16-MAR-99 4 990316 P3 ARS2 DAR 17-MAR-99 2 990317 P2 ARS2 DIF 18-MAR-99 2 990318 P2 ARS2 STD 19-MAR-99 3 990319 P3 ARS1 STD 20-MAR-99 3 990320 P3 ARS1 STD ===================================================== SCIENCE Science nuggets were: 19-Mar-99: A magnificent cusp 12-Mar-99: Impulsive X flare of May 2, 1998: retrospective 5-Mar-99: A compact beginning for a coronal mass ejection? The March 12 nugget resulted from a request by Sasha Kosovichev, who may have found another MDI wave (but with even more interesting properties). This flare preceded the SXT wave ( -?- ) on May 6, 1998 - see http://www.solar.isas.ac.jp/sxt_co/981225.html. The full list of nuggets is kept on http://www.solar.isas.ac.jp/sxt_co/index.html, and the current week's nugget is also always known as http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html. SEMINARS There were no ISAS seminars scheduled during this interval, owing to the Solar-B meeting during Week 11 and ASJ preparations in Week 12. We will resume after the ASJ meeting in Kyoto Mar. 25. YOHKOH OPERATIONS ISSUES HXT continues in the "cal mode" of observation. In this mode HXT gets 64 energy channels at 8-sec binning, as opposed to 4 channels at 1/2-sec binning. Because we have now accumulated many M-class flares in this mode, we may consider returning to the usual 4-channel mode. We regret that there is no general user software available yet for these HXT data. VISITORS AND PERSONNEL Phil Shirts and Alisdair Davey arrived. Alphonse Sterling returned, newly famous because of his incisive sound bites. TOHBANS (spacecraft operators) Tohbans for week 11 SSOC : S. Masuda, T.Watanabe KSC : A. Shiozawa, T.Takanashi SXT_CO: H. Hudson, T. Metcalf SXT_SW: - Tohbans for week 12 SSOC : S.Kubo, T.Shimizu KSC : T.Takanashi, S.Nagata SXT_CO: H. Hudson SXT_SW: P. Shirts, A. Davey