Upload
lalasa
View
35
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Nonlinear force-free extrapolation of coronal magnetic fields T. Wiegelmann, J.K. Thalmann, B. Inhester. Coronal magnetic field models Nonlinear Force-Free Fields (NLFFF) Consistency criteria for vector magnetograms and preprocessing Evolution of a flaring Active Region - PowerPoint PPT Presentation
Citation preview
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
1
Nonlinear force-free extrapolation of coronal magnetic fields
T. Wiegelmann, J.K. Thalmann, B. Inhester
• Coronal magnetic field models• Nonlinear Force-Free Fields (NLFFF)• Consistency criteria for vector
magnetograms and preprocessing• Evolution of a flaring Active Region• Non-force-free fields• Conclusions
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
2
Force-free magnetic field
j x B ~ 0
Vector magnetogrammeasurements
from Gary,Sol. Phys. 2001
NOTForce-free
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
3
NonLinear Force-Free Fields
• Compute initial a potential field (Requires only Bn on bottom boundary)
• Iterate for NLFFF-field, Boundary conditions:- Bn and Jn for positive or negative polarityon boundary (Grad-Rubin method)- Magnetic field vector Bx By Bz on boundary (MHD-relaxation, Optimization method)
Equivalent
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
4
Grad-Rubin methodAmari et al. 1997,2006, Wheatland 2004,06,07
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
5
MHD-relaxationChodura & Schlueter 1981,Valori et al. 2005
OptimizationWheatland et al. 2000,Wiegelmann 2004
NLFFF-consortium(Schrijver et al. 2006):
Optimization mostaccurate and
fastest method.
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
6
Consistency criteria for vectormagnetograms (Aly 1989)
If these relations are NOT fulfilled on the boundary, then the
photospheric data are inconsistent with the force-free assumption.
NO Force-Free-Field.
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
7
No net force
No net torque
Photosphere
Smoothness
Preprocessed boundary data
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
8
Preprocessing of vector magnetograms(Wiegelmann, Inhester, Sakurai, Sol. Phys. 2006)
• Use photospheric field vector as input.• Preprocessing provides consistent boundary data
for nonlinear force-free modeling.• Boundary is not in the photosphere
(which is NOT force-free).• The preprocessed boundary data
are chromospheric like.
Preprocessing can be improved by including chromospheric observations.
(Wiegelmann, Thalmann, Schrijver, DeRosa, Metcalf,Sol. Phys. 2008)
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
9
Chromospheric H-alpha preprocessing• H-alpha fibrils outline magnetic field lines.• With image-recognition techniques we get
tangent to the chromospheric magnetic fieldvector (Hx, Hy).
• Idea: include a term in the preprocessing tominimize angle of preprocessed magnetic field (Bx,By) with (Hx,Hy).
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
10
Test: Model Active Region(van Ballegooijen et al. 2007, Aad’s model)
Model contains the (not force-free) photospheric magnetic field vector and an almost force-free chromosphere and corona.
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
11
Comparison of NLFFF-codes with Aad’s modelMetcalf et al., Sol. Phys. 2008.-Good agreement for extrapolations from chromosphere.-Poor results for using photospheric data directly.-Improvement with preprocessed photospheric data.
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
12
Prepro-cessing
We test preprocessing with Aad’s model
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
13
Angle <B,H> inChromosphere
Force-free coronalmagnetic Energy
No pre-processing 19o 65%
Classical pre-
processing 9o 97%
H-Alpha pre-processing 1o 100%
Results: Comparison with Aad‘s Model
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
14
Evolution of flaring Active Region NOAA 10540(Extrapolation (optimization) from NAOJ/SFT-vector magnetograms;
Thalmann & Wiegelmann, A&A 2008, in press)
Solar Flare Telescope,Mitaka, Tokyo,(Sakurai et al.1995, operatingsince 1992)
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
15
Flaring Active Region NOAA 10540
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
16
Magneticenergy builds
up and isreleases during
flare
Plan:Study flaring
ARs with highertime cadence
with SDO
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
17
Next step: Magnetohydrostatics
Lorentz force
pressure gradient
gravity
Magnetohydrostatic optimization codeCartesian: (Wiegelmann, Neukirch, A&A 2006)
Spherical: (Wiegelmann, Neukirch, Ruan, Inhester, A&A 2007)
Codes workcorrectly for
smooth test cases
To Do:Application
to Data (STEREO,SDO)
01.04.2008 NJIT-seminarNewark, 01.04. 2008
NJITWiegelmann et al: Nonlinear force-free fields
18