Flares and Active Region Current Systems

These two figures show the spatial relationship between a Solar flare, seen in both thermal and nonthermal X-rays by Yohkoh, and the vertical electric currents seen in the photosphere from a Mees Solar Observatory vector magnetogram. The M3.9 flare occurred in NOAA AR 7765 on 14 August 1994 at S12W08, and peaked in hard X-rays at 17:35:58 UT. The Haleakala Stokes Polarimeter vector magnetogram scan was begun at 16:32 UT. The flare is one of six strong hard X-ray flares observed by Yohkoh and studied in a paper in preparation by visiting scientist Jing Li and collaborators at the University of Hawaii and the National Astronomical Observatory of Japan.

The upper panel shows a Hard X-ray Telescope 23--33 KeV image, created using the pixons method. The low panel shows a Soft X-ray Telescope Al.1 (3--20 Angstrom) image; both use the IDL rainbow color scale. The red and white contours show the photospheric vertical current density (white -- upward, red -- downward) at the 1.5, 3, 4.5, and 6 sigma levels, where sigma = 1.99mA/M^2. The vertical magnetic field changes sign across the green lines. Solar North is up, east to the left. The images include 31 $\times$ 31 pixels with 2.24 arcsecond per pixel. The resolution of the current density maps is only about one-half that of the SXT, and comparable to that of the HXT.

The HXT image shows two bright footpoints; the SXT image shows them to be connected by a loop system that is bright at the top. The current system crosses the principal inversion line of the active region along two paths, one of which parallels the loops seen in soft X-rays. In this flare, and in all six of the major flares of the Li et al. study, the flare occurs at the edge of a current channel, not at the point at which the current density peaks.

The Yohkoh satellie is a project of the Institute of Space and Astronautical Science (ISAS), Japan, with important contributions from the US and UK, under the support of NASA and SERC, respectively. Mees Solar Observatory is supported by NASA.

Les Hieda, Kaila Rhoden, Jing Li, Garry Nitta, Tony Distasio

Janet Biggs, Dick Canfield, Sandy McClymont, Don Mickey, Kevin Reardon

Tom Metcalf, Kristin Blais, Jeffrey Douglas, Wayne Lu, Ken Ventura

Elaine Olsen, Mark Waterson, Litao Jiao, Hugh Hudson, Jean-Pierre Wuelser

Reni Kupke, Barry LaBonte, Alex Pevtsov