The X flares of the new cycle

Science Nugget: Nov 27, 1998

A. Coverage

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.


B. Eruptivity

The question of eruptivity is a key one for our understanding of flare physics. The classical large-scale reconnection model of course requires some form 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.

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