Astronomy and Astrophysics – Astrophysics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sp51a01g&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SP51A-01
Astronomy and Astrophysics
Astrophysics
7500 Solar Physics, Astrophysics, And Astronomy, 7509 Corona, 7519 Flares, 7524 Magnetic Fields, 7531 Prominence Eruptions
Scientific paper
When plasma β >1 then the gas pressure dominates over the magnetic pressure. This ratio as a function along the coronal magnetic field lines varies from β > 1 in the photosphere at the base of the field lines, to β << 1 in the mid-corona, to β > 1 in the upper corona. Almost all magnetic field extrapolations do not or cannot take into account the full range of β . They essentially assume β << 1 , since the full boundary conditions do not exist in the β > 1 regions. We use a basic parametric representation of the magnetic field lines such that the field lines can be manipulated to match linear features in the EUV and SXR coronal images in a least squares sense. This research employs free-form deformation mathematics to generate the associated coronal magnetic field. In our research program, the complex magnetic field topology uses Parametric Transformation Analysis (PTA) which is a new and innovative method to describe the coronal fields that we are developing. In this technique the field lines can be viewed as being embedded in a plastic medium, the frozen-in-field-line concept. As the medium is deformed the field lines are similarly deformed. However the advantage of the PTA method is that the field line movement represents a transformation of one magnetic field solution into another magnetic field solution. When fully implemented, this method will allow the resulting magnetic field solution to fully match the magnetic field lines with EUV/SXR coronal loops by minimizing the differences in direction and dispersion of a collection of PTA magnetic field lines and observed field lines. The derived magnetic field will then allow β > 1 regions to be included, the electric currents to be calculated, and the Lorentz force to be determined. The advantage of this technique is that the solution is (i) independent of the upper and side boundary conditions, (ii) allows non-vanishing magnetic forces, and (iii) provides a global magnetic field solution, which contains high- and low- β regimes and maximizes the similarity between the field lines structure and all the coronal images of the region. The coronal image analysis is crucial to the investigation and for the first time these images can be exploited to derive the coronal magnetic field in a well-posed mathematical formulation. This program is an outgrowth of an investigation in which an extrapolated potential field was required to be "inflated" in order to have the field lines match the Yohkoh/SXT images (Gary & Alexander 1999, Solar Physics, 186, 123). The field lines were radially stretched resulting in a better match to the coronal loops of an active region. The PTA method of radial and non-radial deformations of field lines to provide a match to the EUV/SXR images will be presented.
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