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

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

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aas...200.0307b&link_type=abstract

American Astronomical Society, 200th AAS Meeting, #03.07; Bulletin of the American Astronomical Society, Vol. 34, p.642

Astronomy and Astrophysics

Astronomy

Scientific paper

Three-dimensional sunspot coronal magnetograms were derived from coordinated extreme-ultraviolet (EUV) and radio observations of NOAA regions 8108 (N21E18 on 1997 November 18) and 8539 (N20W12 on 1999 May 13). 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 the differential emission measure (DEM) and the plasma electron density for each spatial pixel (along each line of sight) within both regions. These were subsequently used to calculate maps of the expected thermal bremsstrahlung brightness temperature at the Very Large Array (VLA) radio observing frequencies of 1.4, 4.9, 8.4, and 15 GHz. The thermal bremsstrahlung maps reproduce neither the structure nor the intensity of the observed maps, and indicate that thermal gyroemission must dominate the observed radio emission. The radio observations were used to constrain the magnetic scale height and the gross temperature structure of the atmosphere. These, along with the DEM, electron density, and observed radio brightness temperature maps, were used to derive the temperature distribution of the coronal magnetic field strength B(T) that reproduced simultaneously the observed right-hand and left-hand circularly polarized emission at the radio observing frequencies for each spatial pixel in the images. Magnetic field strengths corresponding to 3rd harmonic gyroemission at 4.9 GHz (580 Gauss) are found in coronal plasmas at temperatures as high as 3.2 MK, while magnetic field strengths corresponding to 3rd harmonic gyroemission at 15 GHz (1800 Gauss) are found in coronal plasmas at temperatures as high as 1.6 MK. B(T) was ultimately converted to B(h) and compared with extrapolations from photospheric magnetograms.

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