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Title: Photospheric and coronal magnetic fields

Abstract

Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

Authors:
 [1]
  1. (USAF, Geophysics Laboratory, Hanscom AFB, MA (United States))
Publication Date:
OSTI Identifier:
5030606
Alternate Identifier(s):
OSTI ID: 5030606
Report Number(s):
CONF-910878--
Journal ID: ISSN 0034-6853; CODEN: RGPSB
Resource Type:
Conference
Resource Relation:
Journal Name: Reviews of Geophysics and Space Physics; (United States); Journal Volume: 29; Conference: 20. general assembly of the International Union of Geodesy and Geophysics (IUGG), Vienna (Austria), 11-24 Aug 1991; Related Information: Shea, M. A
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; PHOTOSPHERE; MAGNETIC FIELDS; SOLAR CORONA; CHARGE-COUPLED DEVICES; CORRELATIONS; INFRARED SPECTRA; RESEARCH PROGRAMS; SOLAR GRANULATION; SPATIAL RESOLUTION; SUNSPOTS; USA; ATMOSPHERES; DEVELOPED COUNTRIES; NORTH AMERICA; RESOLUTION; SEMICONDUCTOR DEVICES; SOLAR ACTIVITY; SOLAR ATMOSPHERE; SPECTRA; STARSPOTS; STELLAR ACTIVITY; STELLAR ATMOSPHERES; STELLAR CORONAE 640104* -- Astrophysics & Cosmology-- Solar Phenomena

Citation Formats

Sheeley, N.R., Jr. Photospheric and coronal magnetic fields. United States: N. p., 1991. Web.
Sheeley, N.R., Jr. Photospheric and coronal magnetic fields. United States.
Sheeley, N.R., Jr. Tue . "Photospheric and coronal magnetic fields". United States. doi:.
@article{osti_5030606,
title = {Photospheric and coronal magnetic fields},
author = {Sheeley, N.R., Jr.},
abstractNote = {Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.},
doi = {},
journal = {Reviews of Geophysics and Space Physics; (United States)},
number = ,
volume = 29,
place = {United States},
year = {Tue Jan 01 00:00:00 EST 1991},
month = {Tue Jan 01 00:00:00 EST 1991}
}

Conference:
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  • Daily magnetogram observations of the large-scale photospheric magnetic field have been made at the John M. Wilcox Solar Observatory at Stanford since May of 1976. These measurements provide a homogeneous record of the changing solar field through most of Solar Cycle 21. Using the photospheric data, the configuration of the coronal and heliospheric fields can be calculated using a Potential Field -- Source Surface model. This provides a 3-dimensional picture of the heliospheric field-evolution during the solar cycle. In this report the authors present the complete set of synoptic charts of the measured photospheric magnetic field, the computed field atmore » the source surface, and the coefficients of the multipole expansion of the coronal field. The general underlying structure of the solar and heliospheric fields, which determine the environment for solar - terrestrial relations and provide the context within which solar-activity-related events occur, can be approximated from these data.« less
  • Daily magnetogram observations of the large-scale photospheric magnetic field were made. These measurements provide a homogeneous record of the changing solar field through most of Solar Cycle 21. Using the photospheric data, the configuration of the coronal and heliospheric fields can be calculated using a Potential Field -- Source Surface model. This provides a 3 dimensional picture of the heliospheric field evolution during the solar cycle. This note announces the publication of UAG Report 94, an Atlas containing the complete set of synoptic charts of the measured photospheric magnetic field, the computed field at the source surface, and the coefficientsmore » of the multipole expansion of the coronal field. The general underlying structures of the solar and heliospheric fields, which determine the environment for solar-terrestrial relations and provide the context within which solar-activity-related events occur, can be approximated from these data. The provision of a homogeneous data set of the solar magnetic field over nearly an entire sunspot cycle in a convenient, inclusive package will stimulate the studies of the large-scale structures of the solar and heliospheric magnetic field, encourage others to consider the relationship of the large-scale, ambient field structures to activity on short-time scales and smaller spatial scales, and enable the inclusion of the heliospheric field in analyses of solar-terrestrial relations.« less
  • The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.
  • The magneto-frictional method for computing force-free fields examines the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. The energy of the sheared field can be arbitrarily large compared with the potential field. It is possible to fit the magnetic energy, as a function of shear amplitude, by a simple functional form. The fit parameters depend only on the distribution of normal field in the photosphere and the form of the shearing displacement. The energy is relatively more enhanced if the shear occurs: (1) where the normal field is strongest;more » (2) in the inner region of the dipole, near the axis; or (3) over a large fraction of the dipole area.« less