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

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: image, using a set of Gegenbauer polynomials, where ω(λ) is the angular velocity at latitude λ. The coefficients image, and image are free of crosstalk. We found that ≈9-day periodicity is statistically highly significant in the variations of image at the maximum of solar cycle 22. A similar periodicity is found in the variations of image during the descending phase of the cycle 22 with significant on ⩾99.9% confidence level. At this cycle maximum, a 30–40 day periodicity is found to be dominant among the variations in image, and this periodicity is found in image 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 periodicities of the differential rotation and TSI have a relationship with the production and the emergence rates of the large-scale solar magnetic flux.