Plasma ejection and flow

Science Nugget:  May 21, 1999

Introduction

In the early part of this week the Sun was fairly active, producing a number of impressive flares (see above). On 17-May two events closely spaced in time erupted from the same region on the west limb; both flares were associated with the ejection of plasma. We'll show some images of this plasma motion. Some previous science nuggets have also dealt with plasma ejections from flares. Browse through the master list to find some of these discussions and more images.

The Flares

The events under discussion here took place between 03:40 and 05:30 UT on 17-May. As shown in the GOES X-ray light curve, the peak of the first event was at about the C4 level; the second event was bigger, peaking at just over M2. This image shows the appearance of the Sun at 03:08 UT, just before the first flare; the location of the two flares is shown in the boxed region at the west limb.

Plasma motion

What makes these flares interesting is the ejection of plasma from the flaring region. In the movies linked below, one can see plasma flowing away from the bright overexposed kernel of the flare. In this field of view, north is toward the top of the frame, and the solar limb cuts more or less directly across the middle of the image. (See the field of view plot above for orientation.)
 

Links to movies:

JAVAScript movie (820 kbyte) Animated GIF movie (804 kbyte) MPEG movie (71 kbyte)
 

The sudden brightening at 04:57 UT is the second flare. One can observe plasma flowing northward from the flare site, into the nearby structures just at the top edge of the field of view. Furthermore, the plasma impacting the northern structure appears to be deflected in two directions, as if the path of the ejection is "forked". The simplest explanation is that the plasma follows the magnetic field lines, and the different field lines leading out of the flaring region go in different directions.

The field of view of these images is quite large: 10.5 x 10.5 arcmin. The angular resolution is 9.8 arcseconds per pixel (i.e., seven thousand kilometers per pixel). Thus the path of the ejected plasma is some 140 thousand kilometers, and the inferred speeds are between 350-600 km/sec. This is not so extreme, but falls neatly into the range of speeds observed for ejecta from other flares (e.g., Shibata et al. 1995, ApJL, 451, L83). It is interesting that the ejected material in the present case is preferentially channeled along the magnetic field lines connecting to the structure in the north. This stands in distinct contrast to other examples of flare ejecta which have not been so narrowly focused; see for example the ejection movies of this previous nugget. Instead the present case is probably more similar to the "Jets in Giant Interconnecting Loops" described in the nugget for Week 7, 1999.


May 21, 1999: David McKenzie
(mckenzie@isass0.solar.isas.ac.jp)