Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions

Radio observations of some active regions (ARs) obtained with the Nobeyama radioheliograph at λ=1.76cm are used for estimating the magnetic field strength in the upper chromosphere, based on thermal bremsstrahlung. The results are compared with the magnetic field strength in the photosphere from observations with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar Observing Station of Beijing Astronomical Observatory. The difference in the magnetic field strength between the two layers seems reasonable. The solar radio maps of active regions obtained with the Nobeyama radioheliograph, both in total intensity (I-map) and in circular polarizations (V-map), are compared with the optical magnetograms obtained with the SMFT. The comparison between the radio map in circular polarization and the longitudinal photospheric magnetogram of a plage region suggest that the radio map in circular polarization is a kind of magnetogram of the upper chromosphere. The comparison of the radio map in total intensity with the photospheric vector magnetogram of an AR shows that the radio map in total intensity gives indications of magnetic loops in the corona, thus we have a method of defining the coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysing the I-maps, we identified three components: (a) a compact bright source; (b) a narrow elongated structure connecting two main magnetic islands of opposite polarities (observed in both the optical and radio magnetograms); (c) a wide, diffuse, weak component that corresponds to a wide structure in the solar active region which shows in most cases an S or a reversed S contour, which is probably due to the differential rotation of the Sun. The last two components suggest coronal loops on different spatial scales above the neutral line of the longitudinal photospheric magnetic field.

Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions

Radio observations of some active regions (ARs) obtained with theNobeyama radioheliograph at λ=1.76 cm are used for estimating the magnetic fieldstrength in the upper chromosphere, based on thermal bremsstrahlung. The resultsare compared with the magnetic field strength in the photosphere from observa-tions with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar ObservingStation of Beijing Astronomical Observatory. The difference in the magnetic fieldstrength between the two layers seems reasonable. The solar radio maps of active re-gions obtained with the Nobeyama radioheliograph, both in total intensity (I-map)and in circular polarizations (V-map), are compared with the optical magnetogramsobtained with the SMFT. The comparison between the radio map in circular polar-ization and the longitudinal photospheric magnetogram of a plage region suggeststhat the radio map in circular polarization is a kind of magnetogram of the upperchromosphere. The comparison of the radio map in total intensity with the photo-spheric vector magnetogram of an AR shows that the radio map in total intensitygives indications of magnetic loops in the corona, thus we have a method of definingthe coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysingthe I-maps, we identified three components: (a) a compact bright source; (b) a nar-row elongated structure connecting two main magnetic islands of opposite polarities(observed in both the optical and radio magnetograms); (c) a wide, diffuse, weakcomponent that corresponds to a wide structure in the solar active region whichshows in most cases an S or a reversed S contour, which is probably due to thedifferential rotation of the Sun. The last two components suggest coronal loopson different spatial scales above the neutral line of the longitudinal photosphericmagnetic field.