Quasi 9 and 30–40 days periodicities in the solar differential rotation

Abstract

Using the daily Mt. Wilson Doppler velocity data during 1986–1994 (solar cycle 22), we studied the short-term variations of the order of a few days to a month timescales in the solar differential rotation. We represent the differential rotation in the form: ω (λ) = View the MathML source+View the MathML source (5 sin2 λ-1)+View the MathML source (21 sin4 phi - 14 sin2 λ+1), using a set of Gegenbauer polynomials, where ω (λ) is the angular velocity at latitude λ. The coefficients View the MathML source, View the MathML source, and View the MathML source are free of crosstalk. We found that ≈ 9-day periodicity is statistically highly significant in the variations of View the MathML source at the maximum of solar cycle 22. A similar periodicity is found in the variations of View the MathML source during the descending phase of the cycle 22 with significant on greater-or-equal, slanted 99.9% confidence level. At this cycle maximum, a 30–40 day periodicity is found to be dominant among the variations in View the MathML source, and this periodicity is found in View the MathML source during almost throughout the period 1986–1994. The ≈ 9-day periodicity in the variation of the differential rotation approximately matches with the known quasi 10-day periodicity in the total solar irradiance (TSI) variability. Hence, we speculate that there exists a relationship between the differential rotation and TSI variability. We suggest that the 9–10 day eriodicities of the differential rotation and TSI have a relationship with the production and the emergence rates of the large-scale solar magnetic flux.