Radio Versus EUV/X-Ray Observations of the Solar Atmosphere |
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Authors: | White SM |
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Institution: | (1) Department of Astronomy, University of Maryland, College Park, MD , 20742, U.S.A |
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Abstract: | This paper reviews the contrasting properties of radio and EUV/X-ray observations for the study of the solar atmosphere. The
emphasis is placed on explaining the nature of radio observations to an EUV/X-ray audience. Radio emission is produced by
mechanisms which are well-understood within classical physics. Bremsstrahlung tends to be dominant at low frequencies, while
gyro-resonance emission from strong magnetic fields produces bright sources at higher frequencies. At most radio frequencies
the images of the Sun are dominated almost everywhere by bremsstrahlung opacity, which may be optically thick or thin depending
on circumstances. Where gyro-resonance sources are present they may be used as sensitive probes of the regions above active
regions where magnetic field strengths exceed several hundred gauss, and this unique capability is one of the strengths of
radio observations. Typically a gyro-resonance radio source shows the temperature on an optically thick surface of constant
magnetic field within the corona. Since each radio frequency corresponds to a different magnetic field strength, the coronal
structure can be `peeled away' by using different frequencies. The peculiarities of radio observing techniques are discussed
and contrasted with EUV/X-ray techniques. Radio observations are strong at determining temperatures and coronal magnetic field
strengths while EUV/X-ray observations better sense densities and reveal coronal magnetic field lines: in this way the two
wavelength domains are nicely complementary. |
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