Measurements of the magnetic field and the gradient of temperature in the solar atmosphere above a flocculus using radio observations

Abstract

Simultaneous observations made at several wavelengths in microwave range using the high spatial resolution of radiotelescope RATAN-600 make it possible to develop methods of measuring the magnetic fields in the solar corona and the chromosphere. In this paper we develop a method of measuring the magnetic fields from thermal bremsstrahlung and demonstrate it, using observations of a flocculus (plage) during August 1-3, 1977. The observations show that the flocculus under investigation possessed bipolar magnetic structure with peak to peak amplitude of magnetic field strength of about 40 G at the level of the upper chromosphere and the transition region (with a r.m.s, error of 5.7 G for favourable conditions). The radio astronomical map of the magnetic field is in agreement with the Mt. Wilson magnetic field map to within the experimental error. It follows that the average longitudinal magnetic field above the ftocculus does not drop significantly with height above the photosphere up to the CCTR (chromosphere-corona transition region). An analysis of the spectra of polarized radio emission also gives an opportunity to determine the temperature gradient in the CCTR (which proved to amount to about 1000 K km -1 and to follow their variation with height.

Coronal Magnetic Fields Derived From Simultaneous Microwave and Euv Observations and Comparison With the Potential Field Model

“…Subsequently, the intensity (I) and polarization (V) components are given by Bogod & Gelfreikh (1980) derived the following relationship between the observed polarization degree (V/I) and the longitudinal magnetic field of the radiation source B l :…”

“…Bogod & Gelfreikh (1980) measured the magnetic field strength in the upper chromosphere as approximately 40 G from one-dimensional observations of RATAN-600 in the microwave range. Grebinskij et al (2000) observed the circular polarization of bremsstrahlung at 17 GHz using the Nobeyama Radioheliograph (NoRH;.…”

Sunspots at centimeter wavelengths

“…This characteristic radio morphology found with the WSRT has continued to be discussed with the VLA observations (Vourlidas et al 1997, Zlotnik et al 1998. In contrast, observations with the RATAN-600 have emphasized the spectral information available at 5 frequencies with 1-D spatial resolution (Akhmedov et al 1982;Bogod & Gelfreikh 1980, Krüger et al 1986). In these works, extensive calculations of theoretical radio spectra and maps of intensity and polarization were compared with the corresponding observations for agreement.…”

Radio Emissions from Solar Active Regions

“…The polarization of free-free emissions has been observed with the RATAN-600 (Bogod and Gelfreikh 1980), the VLA (Schmelz et al 1992) and the NoRH (Shibasaki et al 1994;. If the observation is made at a frequency where both RCP and LCP emissions are optically thin, one can simply determine the line-of-sight magnetic field in the source from the degree of circular polarization (12) assuming that the In the contour images, contours are plotted at 5%, 10%, .…”

“…The polarization of free-free emission could be used to determine the line-of-sight component of the coronal magnetic field (Bogod and Gelfreikh 1980). On the other hand, gyro-resonant emission is, in general, very optically-thick and otherwise too weak to be used for polarization measurement.…”