Intense Flares Without Solar Energetic Particle Events

N. V. Nitta (LMSAL), E. W. Cliver (AFRL), H. S. Hudson (UCB)

Abstract:

We study favorably located (western hemisphere) X-class flares that were not associated with solar energetic particle (SEP) events. Three of the five such flares that occurred during the present cycle lacked coronal mass ejections (CMEs), consistent with the current paradigm. Soft X-ray data for these events show outward moving loops above the main flare loop during the impulsive phase, consistent with plasmoid-induced reconnection models. However, the outward moving loops appear to stop at a certain distance. We speculate that they are held back by overlying magnetic field, as implied in soft X-ray images. The flare that was associated with a CME (but not an SEP event) showed a fast (up to 2000 km/s) and unconstrained ejection, but it was on a small scale, as compared with ejections in SEP-associated flares, presumably explaining the rather narrow CME. These flares remind us of the need to understand flares in general, not just as a consequence or a secondary part of CMEs.

Something to remember:

During 1997-2001, a total of 22 SEP events occurred whose >10 MeV proton flux exceeded 100 PFU (Particle Flux Units), according to the list maintained by J. Kunches at NOAA/SEC. Most (18/19) of these intense SEP events that occurred during SOHO operations were accompanied by CMEs. Almost all these CMEs accompany >M5 flares (15/18, or 17/18 if we include likely big flares on the backside).

From the flare list, however, only less than 10 out of the 56 X-class flares during the same period are associated with >100 PFU SEP events. All of the 9 events with LASCO coverage show extended (>200 degrees) CMEs. But we still tend to expect particles from big flares in the well-connected longitudes.

Date Start Peak End Class Location

27-Nov-1999 12:05 12:12 12:16 X1.4 S15 W68

2-Mar-2000 08:20 08:28 08:31 X1.1 S14 W52

30-Sep-2000 23:13 23:21 23:28 X1.2 N07 W90

2-Apr-2001 10:04 10:14 10:20 X1.4 N15 W60

25-Nov-2001 09:45 09:51 09:54 X1.1 S23 W71

List of X-class flares (>W30) not associated with SEPs

The following figures show the Yohkoh/SXT full disk image at the beginning of or slightly before the flare (in reversed orange), the Wind/WAVEs dynamic spectrum (with the GOES 1-8 A light curve superposed), the Yohkoh/HXT light curves in 14-23 keV and 33-53 keV channels (again with the GOES light curve, in dotted line) for a shorter interval (indicated in the WAVES spectrum), the SXT flare sequence images (in green) with a 10’x10’ field of view at the location marked on the full-disk image. The times of these images are indicated with the HXT light curves.

This flare shows a slow (<40 km/s) ejection in SXT data as indicated by the white arrow. But it does not move beyond some point, at which the preflare longer exposure image indicates a closed loop structure (indicated by the black arrow). Indeed, no CME was observed. Essentially radio quiet, but close examination of a metric dynamic spectrum has revealed a weak type II burst (A. Klassen, 2002 personal communication.)

This flare, as discussed in detail by Green et al. (2002), is even less dramatic (no CME, no type II’s or type III’s). A similar ejection can be traced to a certain height (the white arrow), but it does not move beyond it. The presence of an overlying loop system is indicated (by the black arrow).

This flare shows a fast (up to 2000 km/s) and unconstrained ejection as indicated by the white arrow.But it was still on a small scale, and the associated CME was rather narrow.

This flare occurred at the start of the largest SEP event in this cycle. It is shown here for comparison with non-SEP events. Prior to the flare we see a typical S-shaped region. The ejection (the western part of the sigmoid) was on a much larger scale than the previous example.

Conclusions:

The intense flares not associated with SEPs do not show large-scale ejections or global waves (as discussed in Nitta et al. 2002).

These flares may help us understand how much of flare brightening is due to the ejective processes or how much to the essentially non-ejective small scale processes (cf. Cliver 1995).

References:

Cliver, E. W. 1995, Sol. Phys., 157, 285

Green, L. M., Matthews, S. A., van Driel-Gesztelyi, L., Harra, L., & Culhane, J. L., 2002, Sol, Phys., 205, 325

Nitta, N. V., Cliver, E. W., & Tylka, A. J. 2002, to be submitted to ApJL in Dec 2002