NUGGET INDEX FOR 1998

	980110 : The coherent dimming of the entire corona Coherent coronal dimming is hinted at by the continuous exponential decay of the GOES plot. Rather than the occultation of an active region by the Sun's limb, could it be the coherent decay of the many dim regions in the absence of new coronal flux injection?
	980117 : The curiously smooth emergence of AR8131 This active region showed initial x-ray brightening of stable structures without any obvious flaring. The initial behavior of AR8131 is rather inconsistent with the usual picture. The solution lay in the SXT image, showing two separate emergences.
	980124 : A typical data request The Yohkoh chief observer often gets requests about data at specific times of interest to somebody. In this case the request dealt with an IPS phenomenon seen on 12 Jan. 1998 but shows only effects attributable to solar rotation and the normal coming and going of miscellaneous things.
	980131 : The X-ray Doppler Telescope (XDT) The XDT rocket consists of an innovative X-ray telescope with narrow pass bands in the red and blue wings of the Fe XIV emission line, enabling it to measure the coronal 'line of sight' velocity field. From an SXT perspective, its success has been an important step scientifically.
	980207 : A peaceful day on the X-ray Sun The solar activity was very low this week, much like during solar minimum. However, there were some nice eruptive events, which did not produce much X-ray emission. News of a successful XDT launch accompanied news of further SXT entrance filter deterioration.
	980214 : Observations of expanding Active Region loops The SXT collaborated with SOHO in observing the expansion of coronal loops in the outer portions of active regions. SXT observed slow motion (10-30 km/s) in AR 8151, however it remains for Doppler analysis to show whether this is plasma motion or the successive brightening of loops.
	980221: Refinement of Eclipse planning The SXT plans for the YOHKOH partial Solar eclipses. A series of rapid quarter resolution (256x256) full sun images and partial images will hopefully show grazing occultation of any active regions that are present at that time..
	980227 : An X-ray Solar eclipse The highlight this week was of course the solar eclipse. Partial-Sun images 10 seconds apart were acquired of a small active region just on the edge of the moon's apparent path. Available are full-Sun movies of the eclipse to view.
	980306 : An extraordinarily high latitude region This week saw an extremely large-scale postflare loop system that apparently arose in an active region just crossing the E limb at the amazing latitude N48. It is seen edge on and was probably associated with a massive CME projected outwards to the side.
	980313 : Loops interconnecting same-hemisphere active regions These loops interconnect two high latitude active regions in the south, one region of which produces an M class flare. After the flare the interconnecting loops change into loops that seem to have evolved via some subtle mechanism associated with the energy released from the flare.
	980320 : A stable filament channel with a hot core A retrospective nugget examining the unusually stable filament structure that was clearly visible for 3 rotations in July 1997. The core of this structure is clearly x-ray hot. This phenomena is rarely observed since it needs to acquire a special orientation.
	980327 : AR dependence on flare characteristics During 22-27 March 1998, there was one flare a day that was more intense than C5. Although not comprehensively covered by YOHKOH they seemed to vary according to their region, producing cusps, or not.
	980403 : Message from the back side of the Sun Emission from the Southern limb, presumably due to a large region on the back side of the Sun, was observed to be occasionally dynamic. When the region rotated into view it was no longer at high latitudes suggesting a dynamic nature.
	980410 : Further analysis of the 7-Apr-97 CME Flare This major event demonstrates the characteristic sigmoid signature of a preflaring active region. This region was also comprehensively covered by the EIT, and joint analysis at the SoHO-Yohkoh Workshop at ISAS proved particularly insightful.
	980417 : Growth and Decay of AR 8203 We notice four C6-9 flares around 15-Apr-98, all from region AR 8203. The region eventually appeared to exhaust itself in the succession of flares, one of which was associated with a CME as observed by LASCO.
	980424 : Proton flare of April 20 Excellent coverage by SXT of this flare, including the pre-flare event before SXT switched automatically to flare mode coverage.
	980508 : M flare ejecta and Loop filling Yohkoh successfully observed the M class flare from region NOAA 8210 that threw off material. This is viewable as movies taken in SXT's flare mode and also graphically demonstrates the filling of coronal loops near the flare origin.
	980515 : Observations by a Solar spacecraft Flotilla A unique opportunity to make coincident observations by three telescopes (Yohkoh, SoHO and TRACE) of the same Solar region. This week saw plenty of activity including M class flares and the rather extraordinary failure of a massive arcade to erupt.
	980522 : Filament channel seen in many wavelengths This week we examine a filament channel that is currently on the southeast limb. By exploiting many different wavelength images, including SOHO EIT, it is shown that the filament as lying in a channel outlined by bright edges.
	980529 : Connecting structure between distant Active Regions We again encounter a large connecting magnetic structure spanning the gap between two ARs. It appears to fluctuate in brightness over several days, betraying its persistent presence. Whether it formed from smaller structures is not clear, but you can see a movie of this phenomenon.
	980605 : Cycle variation of X-ray Bright Points (XBPs) SXT has observed XBPs since 1993. It has been found that the number of XBPs doesn't appear to follow the number of sunspots. Accounting for bright sunspots drowning out dim XBPs, it appears that the generative dynamos for XBPs and sunspots differ dramatically.
	980612 : A Sigmoidal Learning Curve All is revealed in this nugget which shows the complete coverage of a CME, from the initial S shaped sigmoidal signature to the Geomagnetic interaction as the Earthward bound ejecta reaches the Earth. Successful prediction of these events is one of the motivations behind the Yohkoh.
	980619 : The sigmoid that wouldn't quit A collection of movies that act as a follow-up to last week's dramatic exhibition. The sigmoid remnants from last weeks eruption showed further eruption potential. Indeed the region once again erupted behind the Southwest limb of the Sun, the event being captured by SXT and LASCO.
	980626 : X-ray transit of Mercury Yohkoh observes the first X-ray transit of Mercury. The observations were used, firstly, to calibrate the SXT and HXT roll positions, and secondly to look for scattered light, since the disc of Mercury should, in principle, appear to be a completely black object.
	980704 : Images of the X2 flare of May 2, 1998 The SXT helps observes this very powerful flare. Before eruption two symmetrical but strongly tilted arcs are seen, these seem to vanish as the flare proceeds to erupt. The ejection is interestingly non-radial initially, but probably straightens out at later times.
	980711 : An amazing triple jet Three simultaneous jets is an extremely rare occurrence. They exhibit similar properties, although one seems to have excited a longer lived loop structure. This all leaves questions as to the mechanism behind this simultaneity and the relation between the corona and the jet shapes.
	980718 : Global connectivity A retrospective nugget from when the sun was at a solar minimum. At that time active regions were embedded in a quiet corona, devoid of large X-ray features. This allowed a less confusing study of this flux emergence.
	980725 : Global CME manifestation in X-rays Another retrospective account, this time of the CME of 5th Oct 1996. This event occupied nearly the entire western hemisphere, originating from a region beyond the limb. Large scale dimming accompanied the CME which caused some of the most widespread events seen by the SXT.
	980801 : Active region seen by SXT and TRACE The combined efforts of the two telescopes sought to identify the signatures of magnetic flux emergence in Active Regions. Coordinated exercises like these are rare but are important in clarifying the mechanisms behind coronal loop heating..
	980808 : Hida Campaign - Jet observed by SXT and TRACE Another nugget dedicated to the search for magnetic flux emergence. The signatures of which include arch filament systems (AFSs), surges, X-ray jets and loop brightenings. These images show a jet, coming from a nicely cusped active region.
	980815 : WSF Campaign - Loop brightening observed by SXT and TRACE The beginning of the Whole Sun Fortnight campaign targeted the magnetic field and coronal morphologies of two active regions in the northern hemisphere. They exhibit developing loop brightening as shown by the TRACE and SXT images.
	980822 : An X4 Eruptive Flare This week Yohkoh comprehensively observed several X class flares from a single Active Region. Accompanying this event was a significant reconfiguration of the coronal surrounding region. This reconnection may be followed in a movie.
	980829 : Solar eclipse as seen by the Yohkoh spacecraft Yohkoh observed four episodes of the solar eclipse that could be seen in SE Asia on 22 August 1998. The apparent complicated motion of the moon is due to Yohkoh's orbital motion around the Earth .
	980905 : Proton flare in AR 8210 This nugget follows the two week period of progressively intensifying flares that began in late April. Yohkoh observers examine one such flare, noting its eruptive nature and lack of an impulsive signature in the hard X-ray time profiles.
	980912 : Geometry of flare loops The appearance of loops projected onto the image plane is considered mathematically. Demonstrating the progressively complex nature of more realistic models. this work is important in describing how these loops are heated.
	980919 : An over-the-limb event This LDE originated from a large Active Region beyond the limb. This event is interesting as it involves a large arcade, which are usually associated with CMEs. In such an event coronal dimming is observed. These observations show such effects.
	980926 : Emerging flux and coronal activity Emergent flux is observed as Arch Filament Systems (AFSs) near active regions, these draw photospheric material out into the corona. When seen in different wavebands the effects of these AFSs do not coincide spatially, perhaps implying a complex heating interaction with the corona.
	981002 : A Compact Loop-top Source This nuggets examines the top region of a M class solar flare near the solar limb. A SOHO-EIT image shows a bright source at the top of the loops. This 2MK gas is cool to the reported Masuda Sources found at the loop-top which can be superhot, 100MK.
	981009 : A potpourri of solar activity This week saw transequatorial interconnecting loops, a flare, a jet and the sigmoidal signature of potentially eruptive regions. The Sun produced several examples of events we've seen in previous nuggets.
	981016 : The Neupert Effect The Neupert Effect states that in a flaring event the Hard X-ray emission is at first proportional to the rate of change of the Soft X-ray emission. This is sometimes observed empirically and sometimes not, however it is a general feature of most theoretical mechanisms.
	981023 : An anniversary sigmoid/halo CME marks SOHO's return A year of nuggets has produced another sigmoidal region. The GOES sensitivity isn't sufficient to allow anything other than a hint of the Neupert Effect for such long lived arcades which flare in this fashion..
	981030 : A fine tracery of hot loops A look back to the CME event of 25th July. The eruptive region shows a fine tracery of loops that appear to move horizontally, in agreement with what was observed at the time. In addition a cool spine is observed in the filament heating process that causes the local corona to cool.
	981106 : Sideways ejections These unusual ejections are identified by their cusps which do not point radically away from the disc center. These flares (nearly up to X class) came from a back to front sigmoidal region. Presumably a strong large scale coronal structure is collimating these unusually oriented flares and jets.
	981113 : Repeated brightening in a flare loop Here we look at a coronal loop associated with a C3 flare. The light curves of this loop show fluctuating brightness, perhaps a pulse that travels along the loop and efficiently reflects where the loop is terminated, although it appears to travel too slowly for an Alven Wave.
	981120 : A hideous daily difference image Images taken a day apart can be used to form 'difference images'. These are useful in showing regions of emergent or changing flux. This example shows a vast interconnection between regions, a cusp and regions of cooling. Such images have great potential to reveal even more.
	981127 : the X flares of the new cycle Already thirteen X-class flares have occurred in this solar cycle and Yohkoh has obtained good coverage for 9 of the them. These help identify the characteristics of plasmoid formation and quite often their eruption.
	981204 : Skinny Arcade or Fat Jet? This feature has the appearance of a fat twisted jet, however it accompanied the disappearance of magnetic filaments. So perhaps this is actually a very skinny arcade instead? Either way it seems it was triggered by microflare/jet activity.
	981211 : A confused arcade? This unusual arcade presents a long axis that is perpendicular to the equator. In the early Solar cycle the strong magnetic fields of the Active Regions may be sufficient to cause high latitude arcades to develop odd orientations which evolve slowly in this fashion.
	981218 : homologous compact flares Yohkoh observes these two non-ejecting almost identical flares. The similarity of the events hints at repeated heating of a single magnetic structure. One perhaps one triggering the other? The heated material may originate from irradiated plasma at footpoints near the bright compact regions.
	981225 : A Moreton wave at last? These large scale coronal shocks are seen frequently in UV light. Here we see, in X-rays, an arc shaped wave front propagating Northwards at speeds exceeding 1000 km/s. It is not clear whether this is in fact a photospheric wave or some magnetic effect coupled to the surface.