The Relationship Between Flare Hard X-Ray Sources and Photospheric Electric Currents

fl206.li_j01
Posted:  25-Apr-95
Updated: 26-Nov-95, 09-Aug-96
Events specified: Flares of 15-Nov-91 22:37 UT, 26-Dec-91 21:36 UT, 16-Jul-92 16:55 UT, 20-Aug-92 09:03 UT, 7-Jun-93 14:15 UT, 4-Jul-93 07:48 UT, and 14-Aug-94 17:35 UT

Authors: J. Li, T. R. Metcalf, R. C. Canfield, J.-P. Wuelser University of Hawaii

T. Kosugi National Astronomical Observatory of Japan

Abstract:

We analyze the spatial relationship between solar flare hard x-ray sources observed with HXT and photospheric electric currents observed at Mees Solar Observatory. Canfield et al. (1991) demonstrated that energetic particle precipitation tends to occur at the edges of sites of high vertical current. They did not, however, have a direct, observation of the particle precipitation and used H-alpha Stark wing emission as a proxy. Canfield et al. (1992) confirmed the H-alpha observation for the 1991 November 15 flare using HXT images as a direct observation of energetic particle precipitation. In this study, we will perform the same analysis on a larger sample of flares to determine how ubiquitous the observed spatial relationship is.

Initially, we will examine seven flares with good coverage from both HXT and MSO:

Date Time NOAA Class

1991 Nov 15   22:37 - 22:38   6919   X1.5
1991 Dec 26   21:36 - 21:38   6985   M4.2
1992 Jul 16   16:55 - 16:56   7222   M6.8
1992 Aug 20   09:03 - 09:04   7260   M2.9
1993 Jun 07   14:15 - 14:22   7518   M5.4
1993 Jul 04   07:48 - 07:49   7530   M1.6
1994 Aug 14   17:35 - 17:37   7765   M3.9

Present Status:

We have analyzed much of the data for the seven events and find preliminarily that the relation between sites of hard x-ray emission and sites of high vertical current is confirmed for all seven events.

References:

Canfield et al., 1991, Phil. Trans. Roy. Soc. London, A336, 381 Canfield et al., 1992, Publ. Astron. Soc. Japan, 44, L111

Update 09-Aug-96

We are about finishing the a paper on the relsationship between HXR sites and vertical electric current in large flares. We are going to submit the paper to ApJ. Here is the abstract from the paper:

Title

What is the Spatial Relationship Between Hard X-Ray Footpoints and Vertical Electric Currents in Solar Flares?

Authors

Jing Li, Thomas R. Metcalf, Richard C. Canfield, and Jean-Pierre W\"ulser Institute for Astronomy, University of Hawaii 2680 Woodlawn Drive, Honolulu, HI 96822, U.S.A.}

Takeo Kosugi National Astronomical Observatory of Japan Mitaka, Tokyo 181, Japan

abstract

We examine the spatial relationship between solar hard x-ray sources observed with the Hard X-Ray Telescope (HXT) aboard Yohkoh and photospheric electric currents observed at Mees Solar Observatory. Canfield \etal\ (1993) concluded that energetic electron precipitation tends to occur at the edge of sites of high vertical current. They did not, however, have a very direct diagnostic of the particle precipitation; they used \Ha\ Stark-wing emission as a proxy. In this paper, we analyze hard x-ray sources and vertical currents in six large flares of M/X x-ray class. Our results confirm that electron precipitation sites avoid strong vertical currents at the photosphere in large flares. The stronger HXR sources coincide with the magnetic footpoints having a small or insignificant vertical current density, and a weak magnetic field. This is consistent with a ``cornucopia''-shaped magnetic morphology in which precipitating electrons are deflected away from the strong magnetic footpoint by magnetic mirroring.

Update 26-Nov-95

We are nearing completion of the manuscript describing our findings on the teambb proposal fl206.li_j01 entitled "The Relationship Between Flare Hard X-Ray Sources and Photospheric..." Details follow:

"What is the spatial relationship between Hard X-Ray footpoints and vertical electric currents?"

Jing Li, Thomas R. Metcalf, Richard C. Canfield, and Jean-Pierre Wuelser Institute for Astronomy, University of Hawaii, Honolulu, HI 96822, U.S.A.

Takeo Kosugi National Astronomical Observatory, Mitaka, Tokyo 181

Abstract

We examine the spatial relationship between solar hard x-ray sources observed with HXT aboard Yohkoh and photospheric electric currents observed at Mees Solar Observatory. Canfield et al (1993) demonstrated that energetic particle precipitation tends to occur at the edge of sites of high vertical current. They did not, however, have a direct observation of the particle precipitation and used Ha Stark wing emission as a proxy. In this paper, we analyze hard x-ray sources and vertical currents in six large flares with M/X x-ray class. Our results show that electron precipitation sites avoid strong vertical currents at the photosphere in large flares. The stronger HXR sources avoid with the magnetic footpoints having high vertical current densitiies, and strong magnetic fields. The weaker HXR sources (if there is one) coincide with the magnetic footpoints having small or insignificant current densities and weak magnetic fields. This is consistent with the "Cornucopia" flare model (Hudson, 1995) in which precipitating electrons are deflected away from the stronger magnetic footpoint by a magnetic mirror.