Measurements of 3-D Sunspot Coronal Magnetic Fields From Coordinated SOHO EUV and VLA Radio Observations

Details Measurements of 3-D Sunspot Coronal Magnetic Fields From Coordinated SOHO EUV and VLA Radio Observations Measurements of 3-D Sunspot Coronal Magnetic Fields From Coordinated SOHO EUV and VLA Radio Observations

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sh32c02b&link_type=abstract

American Geophysical Union, Spring Meeting 2001, abstract #SH32C-02

Physics

7509 Corona, 7524 Magnetic Fields, 7534 Radio Emissions, 7549 Ultraviolet Emissions

Scientific paper

Three-dimensional sunspot coronal magnetograms were derived from coordinated extreme-ultraviolet (EUV) and radio observations of NOAA region 8108 (N21 E18) on 1997 November 18. The EUV spectra and images, obtained with the Coronal Diagnostic Spectrometer (CDS) and the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO) satellite, were used to derive differential emission measure (DEM) distributions for each spatial pixel (i.e., along each line of sight) of the region's images. These were subsequently used to calculate maps of the expected thermal bremsstrahlung brightness temperature at the Very Large Array (VLA) radio observing frequencies of 4.9 and 8.4 GHz. The thermal bremsstrahlung maps reproduce neither the structure nor the intensity of the observed maps, and indicate that thermal gyroemission must also contribute to the observed radio emission. Under the assumptions of a monotonic increase in temperature and a monotonic decrease in magnetic field strength with height above the sunspot, we derived the temperature distribution of the coronal magnetic field strength that reproduced simultaneously the observed right-hand and left-hand circularly polarized radio emission at 4.9 and 8.4 GHz for each spatial pixel in the sunspot maps. This was done by placing harmonics of the radio observing frequencies in appropriate plasma temperature intervals, integrating along the line of sight, and iterating until a solution was obtained. Magnetic field strengths corresponding to 3rd harmonic gyroemission at 4.9 GHz (580 Gauss) are found in coronal plasmas at temperatures as high as 2.2*E6 K, while magnetic field strengths corresponding to 2nd harmonic gyroemission at 8.4 GHz (1500 Gauss) are found in coronal plasmas at temperatures as high as 1.1*E6 K.

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