t. i. kaltman, v. m. bogod st. petersburg branch of special astrophysical observatory, russia
DESCRIPTION
On the Structure of Magnetic Field and Radioemission of Sunspot-related Source in Solar Active Region. A. G. Stupishin, L. V. Yasnov Radio Physics Research Institute, St. Petersburg University, Russia. T. I. Kaltman, V. M. Bogod - PowerPoint PPT PresentationTRANSCRIPT
On the Structure of Magnetic Field and Radioemission of Sunspot-related Source in
Solar Active Region
T. I. Kaltman, V. M. Bogod
St. Petersburg branch of Special Astrophysical Observatory, Russia
A. G. Stupishin, L. V. Yasnov Radio Physics Research Institute, St. Petersburg University, Russia
Goal:
To develop methods of physical condition diagnostics in the transition region and the lower corona on the base of reconstructed magnetic field and observations of radio emission on RATAN-600 radiotelescope.
RATAN-600 characteristics:
frequency range: 0.75 … 18.2 GHz
112 frequencies in R and L polarization
max. angular resolution: 2 arcsec
brightness temperature limit: 5∙10-5 K
To estimate physical conditions in particular active regions with simple configuration AR 10933, AR 10935.
AR 10933
RATAN-600 scans
MDI
Source separation
6 GHz
12 GHz
14 GHz
16 GHz
-282" 19"-207" -131" -56"
sun: 2007/01/05: 5.02[cm]Ta,L
2000 AR 10933:
RATAN scans compare with:
UV 195Å (EIT)
Photosphere Magnetic Field (MDI)
Lines of reconstructed Magnetic Field
Magnetic field reconstruction:
1. Source data of 3D photospheric magnetic field – Hinode/SOT instrumentHinode is a Japanese mission developed and launched by ISAS/JAXA, with NAOJ as domestic partner and NASA and STFC (UK) as international partners. It is operated by these agencies in co-operation with ESA and NSC (Norway).
2. 180-degree ambigity was resolved using minimal temperature method (Metcalf, T.R.: 1994, Solar Phys. 155, 235) with optimization suggested at (Leka, K.D., Barnes, G., Crouch, A.D., Metcalf, T.R., Gary, G. A.,
Jing, J., Liu, Y.: 2009, Solar Phys. 260, 83) (inhomogeneous initial temperature).
3. Potential magnetic field was reconstructed according (Nakagawa, Y., Raadu, M.A.: 1972, Solar Phys. 25, 127; Allissandrakis, C.E.: 1981, Astron. Astrophys.
100, 197) (concerning Bz component is not perpendicular to photosphere).
4. On the base of reconstructed potential field (as initial condition) and full 3D magnetic field on photosphere (as boundary condition) non-linear force-free field (NLFFF) was calculated by Landweber iteration algorithm (Wiegelmann, T.: 2004, Solar Phys. 219, 87).
Gyroresonance levels at 3 cm (10 GHz), 3rd harmonic:
at 1.25 Mm
at 1.75 MmReconstructed magnetic field – 3D view
3D view
AR 10933
dTTbTb ii 1
dheTdT kin
dh
)5()4()3()2()1()( s
Emission transition equation solution:
Optical thickness depends on: • emission mode (o-, x-mode), • wavelength, • angle, • magnetic field, • electron density, • electron temperature.
ffs )(
Calculated maps of brightness temperature
Effective heights of optical thickness = 1
0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4
0,0
5,0x105
1,0x106
1,5x106
2,0x106
h, 104 km
Tkin, K
Observations vs. model
Temperature distribution:
Obtain calculated scans by convolutionwith the telescope beam
Modify distribution
Model parameters adaptation procedure
0.0 0.2 0.4
0.0
0.5
1.0
1.5
2.0
2.5
Tki
n, 10
6 K
0.0 0.2 0.41
10
h, 109 cmh, 109 cm
N, 10
9 c
m-3
Model electron temperature and density
AR 10933
6 8 10 12 14 16 18
0.1
1
10
6 8 10 12 14 16 185
10
15
20
25
30
35
40
45si
ze, a
rcse
c
6 8 10 12 14 16 18
104
105
106
Flu
x, s
fu
Tb, K
, GHz, GHz
, GHz
, GHz6 8 10 12 14 16 18
0.1
1
10
Flu
x (R
-L),
sfu
, GHz , GHz
Flu
x (R
-L),
sfu
6 8 10 12 14 16 180.1
1
10P
ola
riza
tion d
egre
e, %
6 8 10 12 14 16 180
20
40
60
80
100
Left polarization
Right polarization
Observation
Model
Spectra: observations vs. model
Observations vs. model: scansAR 10933
Left
Right
ObservationModel
Difference
6 8 10 12 14 16 18
0
1
2
3
4
5
Flu
x, s
fu
f, GHz
I=(R+L)/2
RATAN-600
gr
ff
Effective heights of the free-free emission
Spectrum by RATAN-600,
gyroresonance (gr) and
free-free (ff) emission mechanisms
AR 10935
ConclusionsMethod of active region physical condition diagnostic, based on
– multiwave observation of polarized emission in centimetric waverange on RATAN-600, – Magnetic field extrapolation,– Calculation of radioemission
allows– To estimate the electron density distribution at different height in different parts of active
region, – To estimate the relative contribution of cyclotron and free-free emission at different
wavelengths,– To estimate the contribution of various cyclotron emission harmonics,– To correct active region structural component sizes estimations.
Analyses based on AR 10933 and 10935 shows that reconstructed magnetic field corresponds to observed sizes of radiosources at high frequencies, but at low frequencies observed sizes is smaller that modeled ones. It can be solved by introduction of different density and temperature distribution over and outside the spot. Another possible reason is not full adequacy of magnetic field reconstruction.
Reconstructed magnetic field of simple one-spot active region can be used to modeling of active region structure and matches well with microwave observations in general.
Comparison of observed and calculated radioemission give us the follow estimation of physical condition in analyzed active regions:
– Low corona begins at the heights 2.0 … 2.3 Mm, – Corona temperature is 2.5 MK at low heights and, possibly, rises to 3.0 MK higher,– Electron density in low corona is about 1.5 … 1.8∙109 cm-3.