26 April 1999 Hugh Hudson CHIEF OBSERVER'S REPORT for Week 17 19-Apr-99 to 25-Apr-99 GENERAL Have we reached solar minimum? We are getting a bit desperate here! The good news is that the ARS2 campaign, staring at the disk passage of a single active region, could proceed safely. There have been no rival regions since the NW limb quieted down, and we felt safe enough to leave SXT in ARS2 over the weekend. On Saturday morning the target AR became conspicuously S-shaped, as noted by the KSC tohbans in GBO mail, and then at about 22:00 we got a B5 flare from the sigmoid. This is in Big Bear and Hawaii time range, so we hope that they got good data. SXT TECHNICAL There was some worry about an overexposure glitch, but that may have been confusion with very bright very compact flares in the NW region just before it disappeared. Otherwise, no problems - we have almost completed a terminator cycle and will resume offpoint terminator preparations for the UVCS campaign coming up in early May. 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/990423.html Index: http://www.solar.isas.ac.jp/sxt_co/index.html This week's Science Nugget comments on a "notch" seen clearly in an active region from ten days ago. This notch structure is a frequently-seen characteristic, but one seldom discussed in the science nuggets (or elsewhere) so far as we're aware. We conclude that coronal heating depends strongly on some other factor than B. CAMPAIGNS SXT continued ARS2 support of the BBSO/Mees/SOHO/TRACE observations of AR 8518. 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 Barry LaBonte departed after a lengthy list of various contributions, including the suggestion that an AR of the type we've discussed might be analogous - structurally - to Konishiki. SEMINARS There was a Yohkoh seminar on 22 April: H. Nakajima (Nobeyama): "Radio and Hard X-Ray Observations of Flares with Sub-Second Time Structures" Quite interesting - trapping of particles occurs, but may differ on longer and shorter time scales! SXT TABLE PLAN, WEEK 18 (26-Apr-99 to 2-May-99) DRAFT The items below show the whole week devoted to the AR stare, which we assume will continue until AR8518 wends its way fully to the west. ________________________________#_______________________________ JST Day UT Start Time Pass Table ID Saturday 23-Apr-99 19:42 3 990423 P3 ARS2 STARE* Monday 25-Apr-99 16:48 2 990425 P2 ARS2 STARE* Tuesday 26-Apr-99 17:03 2 990426 P2 ARS2 STARK* Wednesday 27-Apr-99 17:18 2 990427 P2 ARS2 STIF * Wednesday 27-Apr-99 22:27 5 990427 P5 ARS2 STARE* Thursday 28-Apr-99 15:51 2 990428 P2 ARS2 STARE* Friday 29-Apr-99 16:06 2 990429 P2 ARS2 STARE* Saturday 30-APR-99 14:39 2 990430 P2 ARS2 STARE Sunday 1-MAY-99 14:54 2 990501 P2 ARS2 STARE As previously, the (*) in a table name means that the UT date and the JST date don't match. 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.