SXT Status Report
                       August 30 - September 13, 1998
                               (Weeks 36-37)

                     N. Nitta, H. Hudson, J.-P. Wuelser


SUMMARY

Activity was moderate to high. There were no operational problems for
Yohkoh or for SXT. Joint operations with Tenerife and many other
observatories proceeded under the leadership of Brigitte Schmieder.

SOLAR ACTIVITY

The GOES background level (see the plots, for example, on our weekly SXT Web
pages at http://www.solar.isas.ac.jp/sxt_co/index.html) hovered around the 
mid-B level. There were no X flares and 10 M flares during the interval.
A filament to the northeast of AR 8323 went off outside the Tenerife
observing hours, but the disappearance did not result in X-ray arcades.

OBSERVING CAMPAIGNS

A major campaign based on Tenerife ground-based observations has been
proceeding during Weeks 36/37.

SXT INSTRUMENT STATUS AND CALIBRATION ACTIVITIES

The arrival of Jean-Pierre Wuelser at ISAS marks the beginning of an effort
to straighten out the software and database system for Yohkoh pointing. We
have had some problems in this area and are pondering the options. The
system currently uses the IRU (gyros) on board for short time scales, and
the HXA (aspect sensor for HXT) on longer time scales.  An independent
calibration is the soft X-ray limb in SXT images, as defined by Tom
Metcalf's software.  The present situation is that the HXA limb address 
system we have been using since 1991 may be causing temporary problems 
because of the increasing noise spikes relative to solar output.
If the present system becomes unusable, we can work out an alternative
based on the HXA images (1-D) rather than the on-board determinations of
the limb addresses. We'll make a further report on progress here in the
next issue.

As a part of this activity, we have re-defined the Yohkoh "normal pointing"
twice more, each time over steps of 20-30 arc sec.

Correspondence with Wallops confirmed that one of the key data dumps
from the August eclipse was in fact not recorded. This dump contained two
of the four eclipse episodes and probably some images of the major flare
that happened in between. The loss was a result of mis-communication
between DSN and Wallops, an extremely rare phenomenon - we only know of one
other example during 1998. Clearly we've seen a case of Murphy's Law at
work here.


SCIENCE

As has become our practice, we have a weekly "science nugget" attached
to the Web version of the SXT weekly report. The anniversary of this 
system will be October 24, soon enough, at which time we'll probably 
staple them all together and publish a book! The new nuggets consist of:

12-Sep-98: Geometry of flare loops
 5-Sep-98: Proton flare in AR 8210
29-Aug-98: Solar eclipse: 22-Aug-98

The URL's for these and for the full list of science nuggets are on
http://www.solar.isas.ac.jp/sxt_co/index.html,
and the current week is also always kept on
http://www.solar.isas.ac.jp/sxt_co/SXTweekly.html.

OPERATIONS ISSUES

KSC passes lost to other ISAS spacecraft:

   Week 36: 1 pass lost to Akebono and 3 passes to HALCA.
   Week 37: 2 passes lost to Nozomi, 3 passes to Asuka, 3 passes to
     Haruka

VISITORS AND PERSONNEL

Jean-Pierre Wuelser arrived; George Simnett (ISAS visiting professor)
departed after a three-month visit during which we learned a lot about
particles and the heliosphere.

SEMINARS

Sep.  3 -  H. Hara (NAO): "Latitudinal Distribution of XBPs"

This was a further discussion of the automated XBP-tracking program
initiated by Hara and Nakakubo. In this installment, Hara gave strong
evidence for excesses of XBP occurrence at latitudes of about 60  degrees.
The report shows again how powerful this large database will be for
questions of this type. 

Sep. 10 -  G. Simnett (Birmingham/ISAS), "CIRs: Interpretations and
  Modulation of Cosmic Rays"

This continued the discusssion Simnett offerred in August regarding CIR
behavior. One of the crucial points of relevance here is the model of
coronal magnetic connectivity proposed by L. Fisk, which was inspired by
this kind of particle evidence. The time has clearly come for the
interplanetary evidence to be put together with the remote-sensing view
(Yohkoh's, for example) of the coronal field. It's surely premature but
worth speculating that even the XBP distribution might be related to this
kind of global relationship. 

TOHBANS (spacecraft operators)

Tohbans for Week 36

SSOC  : Sterling, Tonooka
KSC   : Ashizawa, Miyagoshi
SXT_CO: Nitta
SXT_SW: -

Tohbans for Week 37

SSOC  : Naito, Nitta
KSC   : Miyagoshi, Nagata (Kubo, Yashiro, Akiyama)
SXT_CO: Nitta
SXT_SW: -