SXT Status Report February 8 through February 22, 1999 (Weeks 7-8) H. Hudson, L. Acton, D. McKenzie, G. Slater SUMMARY Solar activity was moderate during these two weeks, the GOES level rising to near C but without any X-class flares. SXT and its calibration software have recovered from the entrance-filter rupture at the beginning of February, and everything is now normal. We have been supporting observing programs with ground-based observers (Sac Peak and the VLA) and with TRACE and SOHO, as available. SOLAR ACTIVITY There were five M-class flares during the interval, and two sunspot groups with areas larger than 600 millionths. One of these (NOAA 8458) produced a lovely LDE/CME event (Feb. 16) that resulted in a bright trans-equatorial cusp structure, as described in the science nugget for Feb. 19 (see below). In general these interconnecting loop structures displayed remarkable behavior, and SXT images of the rising phase of this solar maximum show us such structures far better than those of the decline of the past maximum. Unfortunately Yohkoh did not directly observe the Feb. 16 event because of the timing of orbit night. OBSERVING CAMPAIGNS The Sac Peak flare observing campaign, led by Gianna Cauzzi and Roberto Falciani, ended on Feb. 12 as scheduled, and clearly has re-established the truth of Murphy's Law. As soon as they stopped looking, flaring resumed in full force. SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES There is no particular technical news from this epoch. The accumulation of terminator images for the stray-light database continues, following the rupture of Feb. 1, and the operational consequences of this new condition have all been worked out. Normal pointing was redefined on Feb. 20. An annular solar eclipse also occurred on Feb. 16, and incidentally the lunar shadow went straight through the "candle flame" of the LDE cusp structure. R. Kano and T. Watanabe successfully ran the special Yohkoh command sequence allow for the shadow's presence, and SXT serendipitously got some nice images (see the Feb. 19 nugget for one of them). SXT OBSERVING SEQUENCE TABLES ----------------------------------------------------------------- JST Day UT Time Pass Table ID ================================================================= 08-FEB-99 04:56 1 990208 P1 ARS1 TERM 06:39 2 990208 P2 ARS2 STD 09-FEB-99 05:13 2 990209 P2 ARS2 DARKCAL 10-FEB-99 05:29 2 990210 P2 ARS2 DIFF 11-FEB-99 04:02 2 990211 P2 ARS2 STD 13-FEB-99 04:33 2 990213 P2 ARS1 STD 15-FEB-99 2 990215 P2 ARS2 VLA 5 990215 P5 ARS2 VLA 16-FEB-99 2 990216 P2 ARS1 ECLIPSE 17-FEB-99 2 990217 P2 ARS1 DARKCAL 18-FEB-99 2 990217 P2 ARS1 DIF 5 990217 P5 ARS1 STD 19-FEB-99 2 990218 P2 ARS2 VLA 2 990218 P5 ARS2 VLA 20-FEB-99 2 990219 P2 ARS1 STD ===================================================== SCIENCE Although many interesting things happened during these two weeks, by far the most impressive had to do with the transequatorial loops connecting the large N and S active regions, or rather connecting their peripheries. These loops displayed many interesting behavior patterns, including siphon flow, zipper motions, and cusp formation - apparently homologous - as the active regions roiled and moiled. The weekly science nuggets dealt with some of this: 19-Feb-99: Transequatorial loops: the movie 12-Feb-99: Jets in giant interconnecting 5-Feb-99: What holds an arcade up? Actually the question asked on Feb. 5 probably became less easily answerable as the trans-equatorial loops developed. The URL's for these and for the full list of science nuggets can be found on http://www.solar.isas.ac.jp/sxt_co/index.html, and the current week's nugget is also always kept on http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html. A very minor science point - the Yohkoh operators got a chance to see the Feb. 16 M-class flare in H-alpha, in real time, at the Sagamihara City science museum. Quite beautiful! SEMINARS Feb. 18, 1999 M. Shimojo (GUAS/NAO) "Studies of Solar Coronal X-ray Jets" This talk dealt with Shimojo_san's thesis work, a comprehensive observational and theoretical effort on one of Yohkoh's best discoveries, the X-ray jets. There was a great deal of friendly discussion, and also great amazement at the TRACE jet movie that concluded the presentation. YOHKOH OPERATIONS ISSUES HXT has re-entered 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. The effect on SXT is to eliminate the quiet-mode PFI's following a given flare, for the duration of that orbit. We hope that the two major spots at the limb will produce big flares now! VISITORS AND PERSONNEL D. Mckenzie and G. Slater returned to the U.S. TOHBANS (spacecraft operators) Tohbans for week 7 SSOC : R.Kano, M.Sawa KSC : S.Akiyama, T.Ishii SXT_CO: D. McKenzie, H. Hudson SXT_SW: G. Slater Tohbans for week 8 SSOC : K. Akita, J. I. Khan KSC : T. Ishii, S. Kawashima SXT_CO: H. Hudson SXT_SW: G. Slater