Abstract
An investigation of variations in solar radio emission at 3.3 mm wavelength as observed with an antenna of half-power beamwidth of 2.8 arc-min indicates the existence of hot stable regions associated with sunspots. These regions are enhanced from 240 K (4%) to more than 3200K (50%) over the quiet center of the disk temperature of 6 600K. Positions of maximum enhancement occur near the neutral lines of primarily bipolar magnetic fields as determined from magnetograms of the longitudinal component of the field. Fourteen of the 113 regions studied were observed to produce flares reported as importance class 2 or greater during the period from mid-February through mid-August 1967. Eleven of the regions which flared had an enhancement of 8.5% or greater and a temperature gradient of 0.5%/deg or greater.
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Mayfield, E.B., Higman, J. & Samson, C. Variations in solar emission at 3.3 mm wavelength and their relation to flares. Sol Phys 13, 372–388 (1970). https://doi.org/10.1007/BF00153558
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DOI: https://doi.org/10.1007/BF00153558