Abstract
In order to study the long-term periodicity variations of the solar radius, daily solar radius data from 1978 February to 2000 September at the Calern Observatory are used. Continuous observations of the solar radius are difficult due to the weather, seasonal effects, and instrument characteristics. Thus, to analyze these data, we first use the Dixon criterion to reject suspect values, then we measure the cross-correlation between the solar radius and sunspot numbers. The result indicates that the solar radius is in complete antiphase with the sunspot numbers and shows lead times of 74 months relative to the sunspot numbers. The Lomb-Scargle and date compensated discrete Fourier transform methods are also used to investigate the periodicity of the solar radius. Both methods yield similar significance periodicities around similar to 1 yr, similar to 2.6 yr, similar to 3.6 yr, and similar to 11 yr. Possible mechanisms for these periods are discussed. The possible physical cause of the similar to 11 yr period is the cyclic variation of the magnetic pressure of the concentrated flux tubes at the bottom of the solar convection zone.
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