Astronomy and Astrophysics – Astronomy
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh22a01h&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SH22A-01
Astronomy and Astrophysics
Astronomy
7513 Coronal Mass Ejections, 7519 Flares, 7524 Magnetic Fields, 7529 Photosphere
Scientific paper
A common belief is that solar events such as flares and coronal mass ejections (CME) are produced by magnetic field changes. Yet there is scant direct observational support of this idea. Modifications of the instruments used by the Global Oscillation Network Group permit full disk measurements of the line-of-sight component of the photospheric magnetic field to be made every minute. The observations have a resolution of 5 arc sec and a noise level of about 5 G per 2.5 arc second pixel. Several day-long sequences were studied to see if changes of the magnetic field at the times of flares and CMEs could be detected. The magnetograms were viewed as movies after various preprocessing steps. They were also used to make time series of the field strength averaged over the entire disk, over zones of selected latitudes and as coefficients of spherical harmonic transforms of the data. To date no signature of a magnetic field change that can be directly associated with flares or CMEs has been detected. Evidently such associated changes are either below our noise level of a fraction of a Gauss (depending on analysis method), take place predominantly outside the photosphere, or are mainly of a component of the vector magnetic field that is not well represented along the line of sight. This work utilizes data obtained by the Global Oscillation Network Group, managed by the NSO. The NSO is sponsored by the the National Science Foundation through a cooperative agreement with the Association of Universities for Research in Astronomy, Inc. This work was supported in part by ONR award N00014-91-J-1040.
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