SXT Status Report 14 April - 27 April, 1998 (Weeks 16-17) H. Hudson, N. Nitta SUMMARY There have been many flares, including one M and one X, even though the GOES background level was a bit decreased. The largest sunspot group area was only 210 millionths. Yohkoh and SXT continue to operate well. SOLAR ACTIVITY Approximately a dozen C or greater events occurred. These included two rather spectacular over-the-limb events, an M1 proton flare in the SW (April 20) and an X1 in the SE (April 23). The latter originated about a day beyond the limb and had the characteristically sluggish hard X-ray variations associated with an over-the-limb event. It was caught with a new SXT flare observing sequence, which emphasizes ejections, and furthermore the preflare PFIs were properly situated to see the beginnings of the ejection. The coverage was excellent, including Nobeyama. The April 20 event is the subject of this week's science nugget. Again, a beautiful ejection was observed. SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES Data archiving is complete through Week 12 (ending at Spring Equinox). Terminator acquisition continues. No spacecraft re-pointing was necessary. SCIENCE The presence of ISAS Visiting Professor H. Aurass (from Potsdam) stimulated a great deal of new discussion. He is probably the longest-term visitor really knowledgable with meter-wave radio observations, and because SXT and the meter wavelengths both look at regions of similar plasma density, but by very different techniques, comparisons have always been one of the more exciting fields for Yohkoh data analysis. Work continued on the Web presentation of the third SOHO-Yohkoh CDAW (Coordinated Data Analysis Workshop), which took place the week of April 4, with several people cleaning up loose ends. This CDAW really brought us to a good position with respect to "Web reporting" as an alternative to yet another conference proceedings. The scheme of weekly reporting by the SXT Chief Observer on Web pages has continued. The current "science nugget" is now located under the official Yohkoh Web site at ISAS, and its URL is http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html. The previous science nuggets reported by SXT chief observers are listed in http://www.solar.isas.ac.jp/sxt_co/index.html. The newer ones are: 980320.html Cavity with bright core 980327.html AR dependence of flare characteristics 980403.html Message from the back side of the Sun 980410.html Further analysis of the 7-Apr-97 flare CME 980417.html Growth and Decay of AR 8203 980424.html Proton flare, April 20, 1998 The last entry is identical with SXTweekly.html and contains links to current-week operations information. We SXT chief observers seem to like this system - it helps us make current affairs available - and we would always appreciate feedback. We may further reorganize the Web site over the next few weeks. (Note that the Web site will be unreachable approximately between 25-Apr-98 09 UT and 26-Apr-98 09 UT due to power outage at ISAS). OPERATIONS ISSUES Week 16, two KSC passes lost to HALCA. Week 17, two KSC passes lost to HALCA. There were no special joint-observation campaigns during the past two weeks. The future period will see SOHO and TRACE joint observations, including a JOP planned by F. Clette. VISITORS AND PERSONNEL Thompson and Aurass departed; Canfield arrived and leapt into tohban duties. SEMINARS April 16: Huaning WANG (Beijing Observatory & NAOJ) "Magnetic separatrices and solar atmospheric heating in an active region" This was an especially timely talk, with H. Aurass present, because the general problem of coronal field mapping has such strong implications for meter-wave radio observations as well as Yohkoh. The approach taken appears to allow a better determination of the QSL (quasi-separatrix layers) important for 3D reconnection theory. TOHBANS Tohbans for Week 16 SSOC : K. Shibata, S. Yashiro KSC : Y. Nakagawa, T. Shimizu SXT_CO: N. Nitta SXT_SW: - Tohbans for Week 17 SSOC : S. Akiyama, R. Canfield KSC : T. Shimizu, S. UeNo SXT_CO: H. Hudson SXT_SW: -