RATAN-600 (South sector Periscope)

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RATAN-600 (South sector Periscope)
About the Features of the Vertical Magnetic
Field inSolar Corona using Polarization
Observations at Microwaves V.M. Bogod, Special
astrophysical observatory, Russia, vbog_at_sao.ru
L.V. Yasnov St.Petersburg State University,
Russia
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The Problem

• The high-altitude measurements and magnetic field
  distribution in active region above sunspot
  always were an important problem to verify
  existing models at heights from units to hundreds
  of Mm.
• The optical magnetic field measurements are only
  good working on the photosphere level, but on the
  chromosphere and low corona levels the model
  calculations are used. There is a problem with
  direct magnetic field measurements on these
  levels.
• The height of magnetic field on the corona levels
  above sunspot from various models is of about
  2-4 Mm. For example, from the paper Gary, G.
  A. 2001, Solar Physics 203, 71 follows (for the
  potential extrapolation of a photosphere magnetic
  field), that at these heights ?400-700 G, if the
  magnetic field on the photosphere level B 3000
  G.
• From the other side the radio astronomical
  polarization measurements give the opportunities
  to estimate the magnetic field strength on the
  levels of transition region and the low corona.
  It point that the magnetic field decrease with
  height not more than 20 , that is, up to ?2400
  G, if the field at photosphere level ?3000 G
  Akhmedov et al, 1982

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About comparison modelling and the measurements
of height structure of magnetic field in active
region.
Akhmedov etal, S.Ph., 1982
Fig. The reconstruction of magnetic field above
active region is shown according model
approximation Gary, 2001. Red dotted line
coincides with radio measurements and point to
less divergency.
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Fine coronal X-ray structure
SOHO data
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TRACE data
Fine X-ray structures
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Fine coronal X-ray structure?limchuk, 2000,
Solar Physics
Fig1. Full-resolution SXT image from the 26
December 1991 orbit beginning 1758 UT.
Dimensions are 189.00 _ 186.00. Loop footpoints
are marked with stars.
Fig20. Twisted magnetic flux tube of uniform
thickness surrounded by untwisted field that is
expanding with height.
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INTRODUCTION

• 1.Multiwave observations of active region
  polarization emission made at microwaves, can be
  effective tools for the study of magnetic field
  distribution with coronal height for sunspot
  associated sources. In the case the projection
  method is used for determinate the coronal
  heights of magnetic field.
• 2.In the work we use the multi-wave observations
  of radio polarization emission above sunspot at
  microwaves (RATAN-600) together with precise
  magnetic field data (SOHO MDI) in optics.
• 3. For the method it is important to do the
  microwave observations of polarization emission
  at many wavelengths simultaneously.
• 4. For measurements of the magnetic field
  strengths at coronal heights, the cyclotron
  theory is used.
• 5. It was discovered that magnetic fields with
  strength about 1000 Gauss may reach the heights
  of the solar atmosphere from 10 to 40 Mm.

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An example of multiwave solar scan with RATAN-600
(SP)
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Parameters of new spectral-polarization complex
for solar study with RATAN-600

• Frequency coverage 3 GHz 18GHz
• The band of separate channel 100 MHz
• 3. Number of frequency channels 80
• 4. Noise Temperature T 300 ?
• 5. Full dynamic range gt
• 6. Record speed about 2.5 mlsec for each channel
• 7. Recording parameters II(L)I(R)VI(L)-I(R
  )

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Geometrical base of the method
Fig. 1.To the explanation of the projection
effect. The principle of measurement of the
difference in locations of a radio source on the
level of the 3rd gyro frequency harmonic and the
optical structure (sunspot) is shown.
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Technique of determination of the structure of
magnetic field
The aim of processing of the scans of the Sun was
to determine the time dependence of the position
of a chosen detail of an active region in the
polarized emission - Using helio latitude
of a measured detail of AR, we
calculate the location of this detail on the
solar disk in the coordinate system of radio scan
.
Here - helio longitude
We have used the known time dependence of helio
longitude of the sources on the photosphere
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Technique of determination of the structure of
magnetic field (continuation).
Next, we minimized the expression for determining
the values of h and for each wavelength
under the study.
where N is the number of data series used (from 2
to 3).
The polarized radio emission above spot is
effective at frequencies corresponding to the
third harmonic of the electron gyrofrequency. In
this case the magnetic field may be determinate,
like Next, because we have the multi frequency
observations with instant records at each
wavelength, one can plot the dependence B(h) .
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The example of magnetic field measurements for
the AR 10933 and 10935 during Jan 7- 8 , 2007
with RATAN-600
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The height of magnetic field and its 2-D
structure (height latitude)
Magnetic field inclination
For binding of radio measurements of magnetic
field with optical photosphere value we use the
one-dimensional dipole approximation of a
magnetic field according (Takakura,1972
- altitude difference on time
Where d-depth of a dipole under photosphere,
h-height above photosphere Bo
magnetic field on the photosphere level
Here the latitude on the high radio
frequency
(where the magnetic field is maximal)
- the latitude on the arbitrary radio frequency

radius of a spot
Using SOHO MDI data
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Example of NOAA 0953 observations during
03-02.05.2007.
Sun optical map. To the right the AR NOAA 0953
in the form of unipolar spot.
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Comparison the multiwave radio observations
during May 2 3, 2007 with RATAN-600
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AR NOAA 10953 ?? 03-02.05.2007.
Fig.The height distribution of magnetic firld
for AR NOAA 10953. To the right, the MDI SOHO
data pointing to the stable spot structure.
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AR NOAA 10953 ?? 03-02.05.2007.
Fig. The magnetic field lines for AR NOAA 0953.
To the left the dependence of the magnetic field
magnitude on longitude (monotonic
?!) To the right the dependence of magnetic
field height on the horizontal distance X. The
comparison points the height spirality of
magnetic field with width about 0.4 degrees.
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Advantages of the method

• Instant spectra of intensity and polarization
  emission at many frequencies at microwaves.
• High convergence of the methods for study of
  stable active regions.
• The opportunity of determinate of inclination of
  magnetic field profile.
• !

The main errors of the method

• Aberration errors due to decentration of the
  beam. The error depends on wavelength and value
  of desentration. It is corrected by calculation.
• 3. Errors linked with variability of the source
  under study,
• 4. For the accuracy height measurements need the
  binding with optical data about magnetic field
  value on the photosphere.

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• CONCLUSION
• 1.The multiwave polarization radio measurements
  point to diversity of magnetic field structure
  with height.
• The radio data point that the magnetic field
  decrease with height but with less gradient then
  we know from the models.
• The method based on high coordinate measurements
  both in optics and radio, multi wave polarization
  measurements and high spatial resolution.
• 4. The method allow to construct not only
  dependence magnetic field with height, but also
  2-D form of magnetic field strength above a spot.

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THANK YOU FOR ATTENTION!
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About the features of the vertical magnetic
field insolar corona using polarization
observations at microwavesV.M. Bogod, Special
astrophysical observatory, Russia, vbog_at_sao.ru
L.V. Yasnov St.Petersburg State University,
Russia,
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• Thank You for Attention!

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Procedure of the height measurements
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