qs050.klimchuk05 Posted: 11-Mar-93 Updated: 06-Nov-93, 7-Aug-94, 27-May-95, 22-Aug-95, 07-Jul-96 Events specified: N/A
Collaboration: J. Klimchuk (NRL), D. Webb, S. Kahler
CMEs represent disruptions of large-scale structures of closed magnetic fields in the low corona. Although many aspects of CMEs have been well studied, we still know very little about the source regions from which CMEs erupt, especially with regard to the magnetic field configuration at the surface and in the lower atmosphere. We will address this question by locating and studying structures on the disk which are related to the origins of CMEs.
Coronagraph images have revealed that, although CMEs are usually fairly symmetrical at higher heights, they often show a high degree of asymmetry at lower heights overlying active regions and prominences. Also, associated active regions and prominences are of smaller scale than CMEs and often offset from the axis of the CME. First, we will select for study Yohkoh X-ray events on the disk which suggest an eruptive character. Then we will determine the locations of the structures involved with these events with the large-scale magnetic field patterns as delineated by surface polarity patterns and inversion lines. Data used for this project will include synoptic presentations of the polarity patterns and coronal holes from NOAA-SEL, of the photospheric magnetic field from Stanford and NSO-Kitt Peak, of the computed source surface field from Stanford, and of the white light corona from Mauna Loa Observatory. The SXT Synoptic charts being produced (e.g., qs043) should also be useful for our study.
Webb and Kahler bring great expertise to this effort through their many years of experience analyzing and interpreting X-ray data, including imaging data from AS&E telescopes on OSO-4, Skylab and sounding rockets, as well as CME observations from coronagraphs on Skylab, SMM and P-78 and from the Helios photometers.
Required Observations: Thin-filter, full frame SXT images at a cadence of about one frame every hour or orbit. SXT synoptic charts would be helpful but not necessary for the study. The other synoptic charts mentioned above are readily available in Solar-Geophysical Data Bulletins or from other published sources.
Update 07-Jul-96
We submitted a paper to the Journal of Geophysical Research:
Abstract
We use Yohkoh Soft X-ray Telescope (SXT) images of eruptive events visible against the solar disk to examine the coronal structures and the boundaries of the large-scale magnetic fields considered to be involved in coronal mass ejections (CMEs). From an initial list of about 100 large-scale (i.e., >20 deg.) events, we selected five for detailed study. The transient X-ray structures in these events spanned distances across the solar surface ranging from 35 to >100 heliographic degrees, comparable to the spans of white light CMEs observed at the limb. Each of these coronal arcades overlay two or three neutral lines or a single, highly convoluted neutral line in the direction orthogonal to the long axis of the arcade. The results imply that multipolar magnetic systems may be a common configuration of the source fields of many CMEs, as opposed to the common paradigm that CMEs involve the eruption of simple, bipolar structures.
(Original Version as of 7-May-96) We use Yohkoh Soft X-ray Telescope (SXT) images of eruptive events visible against the solar disk to examine the coronal structures and the boundaries of the large-scale magnetic fields that might be involved in coronal mass ejections (CMEs). From an initial list of about 100 large-scale (i.e., >20 degrees) events, we selected five for detailed study. The transient X-ray structures in these events spanned distances across the solar surface ranging from 35 to >100 heliographic degrees, comparable to the spans of white light CMEs observed at the limb. Two or three neutral lines or a single, highly convoluted neutral line were associated with each of these coronal eruptions. The results imply that multipolar magnetic systems may be a common configuration of the source fields of many CMEs, as opposed to the common paradigm that CMEs involve the eruption of simple, bipolar structures.
Update 22-Aug-95
We have begun to develop an algorithm for detecting the occurrence of Earthbound CMEs that is based on the post-eruption soft X-ray arcades that are usually formed. A CME will be deemed to have occurred if the intensity in some minimum number of contiguous pixels is enhanced by some minimum amount over some minimum period of time. We will determine the most appropriate values for these three basic parameters: number of pixels, intensity enhancement, and duration.
Update 27-May-95
We have recently been preparing a manuscript for submission to Geophysical Research Letters. The authors are Webb, Kahler, McIntosh, and Klimchuk. The abstract follows.
We use Yohkoh Soft X-ray Telescope (SXT) images of eruptive events visible against the solar disk to examine the coronal structures and the boundaries of the large-scale magnetic fields involved in coronal mass ejections (CMEs). Starting with a large number of large-scale events, we studied five in detail. The size scales of the transient X-ray structures involved in these events ranged from 35 to >100 heliographic degrees, comparable to the spans of CMEs observed at the limb. Two or three neutral lines or a single, highly convoluted neutral line were associated with all of these coronal eruptions. The results imply that multipolar magnetic systems may be a common configuration of the source fields of many CMEs, as opposed to the common paradigm that CMEs involve the eruption of a simple, single neutral line structure.
Update 7-Aug-94
We have begun to analyze in detail the following events: 12-Nov-91, 27-Apr-92, 01-Jun-92, 17-Jun-92, 04-Nov-92, and 14-Apr-94. Preliminary results were presented by Webb at the spring Solar Physics Division / Americal Geophysical Union meeting in Baltimore and at the July COSPAR meeting in Hamburg, Germany. We have found that some events appear to be related to double neutral lines and changing coronal holes, and we are now attempting to understand the 3-D magnetic configurations that are involved.
Update 06-Nov-93
In July, Dave Webb visited Stanford to make further plans with Jim Klimchuk. It was agreed that Webb and Kahler should begin reviewing the SXT movie for candidate events for which there is a clear LDE (long duration event) signature in the GOES X-ray signal and for which there is good ground-based data. Klimchuk would later identify specific images for detailed analysis. The Yohkoh software was successfully installed on the workstation at AFGL, the home site of Webb and Kahler.