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Abstract
Context.As the coronal magnetic field can usually not be measured
directly, it has to be extrapolated from photospheric measurements into
the corona. Aims.We test the quality of a nonlinear forcefree
coronal magnetic field extrapolation code with the help of a known
analytical solution.Methods. The nonlinear forcefree equations
are numerically solved with the help of an optimization principle. The
method minimizes an integral over the forcefree and solenoidal
condition. As boundary condition we use either the magnetic field
components on all six sides of the computational box in Case I or only
on the bottom boundary in Case II. We check the quality of the
reconstruction by computing how well forcefreeness and
divergencefreeness are fulfilled and by comparing the numerical
solution with the analytical solution. The comparison is done with
magnetic field line plots and several quantitative measures, like the
vector correlation, Cauchy Schwarz, normalized vector error, mean vector
error and magnetic energy. Results.For Case I the reconstructed
magnetic field shows good agreement with the original magnetic field
topology, whereas in Case II there are considerable deviations from the
exact solution. This is corroborated by the quantitative measures, which
are significantly better for Case I.Conclusions. Despite the
strong nonlinearity of the considered forcefree equilibrium, the
optimization method of extrapolation is able to reconstruct it; however,
the quality of reconstruction depends significantly on the consistency
of the input data, which is given only if the known solution is provided
also at the lateral and top boundaries, and on the presence or absence
of flux concentrations near the boundaries of the magnetogram.
Original language  English 

Pages (fromto)  737741 
Journal  Astronomy & Astrophysics 
Volume  453 
Issue number  2 
DOIs  
Publication status  Published  1 Jul 2006 
Keywords
 Sun: magnetic fields
 Sun: corona
 Sun: photosphere
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Dive into the research topics of 'Testing nonlinear forcefree coronal magnetic field extrapolations with the TitovDémoulin equilibrium'. Together they form a unique fingerprint.Projects
 1 Finished

Solar&Magnetospheric Plasma Theory PP/E1: Solar and Magnetospheric Plasma Theory
Neukirch, T., Hood, A. W., Parnell, C. E., Priest, E., Roberts, B. & Wright, A. N.
1/04/07 → 31/03/12
Project: Standard