(Week 48, 1998)
The Soft X-ray Telescope operated well as usual. See the weekly operations report for details. Solar activity was extremely high this week, with four X flares (part of the subject of this week's science nugget, see below).
In the display above (click to enlarge), the colored lines show the times of SXT images that currently are on-line at ISAS. The purple lines are flare mode. The gaps will be considerably reduced when the NASA telemetry arrives and gets reformatted. For a summary index listing of the weekly science reports, click here.
Already thirteen X-class flares have occurred in this cycle, as listed below in the usual NOAA format but with comments regarding Yohkoh coverage and the "eruptivity" of the flare. Note please that only 23 X-class flares occurred during the Yohkoh coverage of the past maximum, so we are well on the way to the peak - HESSI, hurry up please!
Date Time Imp Locus Yohkoh coverage Eruptive commentary 4-NOV-97 05:58 X2.1 2B Full-frame data - (from 06:10:02) 6-NOV-97 11:55 X9.4 S19E64 Good coverage faint ejecta to SW 27-NOV-97 13:17 X2.6 N19W64 Good coverage strong ejecta >13:13 to SE 23-APR-98 05:55 X1.2 S19E105 Good coverage ejecta, fast and slow, to E 27-APR-98 09:20 X1.0 2B S19E54 Rise phase only "slow LDE" with ejecta to E 2-MAY-98 13:42 X1.1 3B S15W15 Rise phase only jet >13:36 to NE 6-MAY-98 08:09 X2.7 S16W67 Good coverage Moreton wave? + loop ejection 18-AUG-98 08:24 X2.8 No coverage - 22-NOV-98 06:42 X3.7 S30WL Main phase only Ejecta to SW (>06:39) 22-NOV-98 16:23 X2.5 S29WL Late rise, peak Ejecta to SW 23-NOV-98 06:44 X2.2 S30WL Decay phase - 24-NOV-98 02:20 X1.0 S30WL From peak only - 28-NOV-98 05:52 X3.3 N17E46 Good coverage Complex ejection to E
The following plots also summarize the Yohkoh coverage graphically, with a similar format as for the weekly GOES plot shown at the top of this page. The yellow line gives the GOES low-channel light curve, and the tick marks show the SXT image times, with purple indicating flare mode. At the time of writing, we had complete databases for all of the events except for one. In the table above, "good coverage" means that flare mode extended across the impulsive phase.
The question of eruptivity is a key one for our understanding of flare physics. The classical large-scale reconnection model of course requires some for of eruption, and subsequent to the discovery of the Masuda flare, with its suggestion of a cusp (eruptive signature?) in a relatively compact flare, a search by Shibata et al. of a complete sample of limb events showed that all of them appeared to have evidence for ejective motions. Is this evidence for the formation and/or eruption of plasmoids?
These X-class flares give us a good opportunity to ask this question where the answer is likely to be "YES". In fact, (Yohkoh) obtained good coverage for 9 of the 13 X flares, where "good" is defined as coverage of the impulsive phase The Yohkoh new-cycle data on major flares thus confirm the Shibata et al. conclusions, namely that ejection is omnipresent. The new-cycle flare data are better than the old data for this purpose, because SXT now runs an "ejection special" program that provides good cadence with large fields of view (10 arc min and 5 arc min), so that we can make a more evenhanded survey for ejectivity.
Of course, simply because a flare ejects matter does not meant that large-scale reconnection has anything to do with energy release! Most of these ejecta are faint, many go at odd angles relative to the local vertical, and in no case do we see obvious inflow as a source of reconnection energy - see the critique of model predictions (.ps file) by Hudson and Khan for more discussion.
Comments to: hudson@isass0.solar.isas.ac.jp