Solar Radius Variations at 48 GHz Correlated with Solar Irradiance

Maps of the whole Sun at 48 GHz made during the period 1991-1993, using the large dish of Itapetinga Radio Observatory with the multibeam system, allowed solar limb determinations with unprecedented precision. From a large sample of maps, the solar radius at 48 GHz is found to vary in time. The observations showed that there is an apparent decrease of the measured radius as the solar cycle declines. We estimated the decrease to be 8'' for half of the solar cycle. The 48 GHz solar radius variations are found to be very well correlated with the solar irradiance.

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