3 April 1999 Nariaki Nitta CHIEF OBSERVER'S REPORT for Week 14 29-Mar-99 to 4-Apr-99 GENERAL The solar activity was low, but the GOES level showed an upturn in the middle of the week as new regions arrived at the east limb. As of midnight of 4/5 April JST, we already count three M-class flares. The northern hemisphere was quite dynamic, with a likely eruption of a polar crown filament (30 March), and another eruption, again associated with a filament, on the NW limb (2 April). SXT TECHNICAL The analysis of the 20-Jan-99 flare (for a preliminary report, see http://www.solar.isas.ac.jp/sxt_co/990122.html ) aroused interesting discussion about the SXT off-axis response. Work is under way to see if appropriate corrections are provided by the program ``SXT_VIGNETTE'', as called in ``SXT_PREP.'' We may need substantial refinement to the program. The decreasing signal level of HXA resulted in substantial uncertainty in the determination of the Yohkoh pointing as derived from HXA limb address data. Jean-Pierre Wuelser has developed new software to make use of HXA scan data, and the result has been very encouraging. There is another problem applicable only to temporary pointing data reformatted after each KSC contact, because of occasional reversals of time tags. This has been a major obstacle for those who try to obtain quantitative results before the official reformatting, normally 3-6 weeks after the data aquisition. Greg Slater is fixing the problem. After the latter problem is completely solved, the whole pointing database from mid-1997 will be regenerated using HXA scan data. In the meantime, a warning message may be sent to the entire Yohkoh team, explaining what the user should be aware of when registering SXT images. SXT SCIENCE For Web material see Current Week: http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html Current Week: http://www.solar.isas.ac.jp/sxt_co/990402.html Index: http://www.solar.isas.ac.jp/sxt_co/index.html The current Nugget discusses flare eruptivity as observed by SXT. It is largely based on the seminar presentation (see below). CAMPAIGNS There were no formal campaigns this week. Please see the general coordination page at: http://sec.noaa.gov/solcoord/solcoord.html For SXT plans, finger campaign@isass0.solar.isas.ac.jp. PERSONNEL No change. SEMINARS Yohkoh Seminar on 1 April. Speaker: S. Akiyama (NAOJ/GUAS), Title: ``The Occurrence Probability of X-ray Plasma Ejections by Solar Flares.'' Although further refinement should be given to the analysis, this is probably the first time serious considerations are given to the effect of background on the detectability of X-ray ejections. SXT TABLE PLAN, WEEK 15 (4-Apr-99 to 10-Apr-99) Jim Klimchuk wants to observe coronal loops with SXT and TRACE to study their widths. We will probably coordinate with TRACE on Wednesday and Thursday. There is a possibility of another CCD bakeout, which was planned for March but was not carried out, so the following plan is taken as very tentative. Please watch out for daily FAX. ________________________________#_______________________________ JST Day UT Start Time Pass Table ID Monday 5-Apr-99 02:52 2 990405 P2 ARS1 DIF Tuesday 6-Apr-99 03:08 2 990406 P2 ARS1 DAR Wednesday 6-Apr-99 23:59 1 990406 P1 ARS2 LOOP Wednesday 7-Apr-99 01:40 2 990406 P2 ARS1 STD Thursday 8-Apr-99 00:13 1 990407 P1 ARS2 LOOP Thursday 8-Apr-99 01:56 2 990407 P2 ARS1 STD Friday 9-Apr-99 00:28 2 990408 P2 ARS1 STD Saturday 10-Apr-99 00:43 2 990409 P2 ARS1 STD Note that we keep the first part of Table ID (yymmdd) with reference to the UT date of the first pass. Continuing requests: KSC & SSOC Tohbans: If any KSC passes are likely to be cancelled (for example due to a typhoon) or an SXT table cannot be uploaded for some reason, please telephone and e-mail the Chief Observer immediately. (sxt_co@isass0.solar.isas.ac.jp, copy to sxt_st@flare2.solar.isas.ac.jp). SSOC Tohban: On the weekly visible diagram, please mark the official five passes first and then cross out those passes that will be given to other satellites. That way we can keep the numbering straight in the Yohkoh software system. SSOC Tohban: SXT operations do not currently include terminator off- pointing. It is unnecessary this week to ask the SXT Chief Observer for terminator off-pointing information. KSC Tohbans: In general flare mode supersedes table upload, ie if a flare is in progress please do not upload a new table, and contact the chief observer. Normally it is OK to go ahead with the planned table without change on the next pass, if it is available. Chief observers should keep an eye on this.