An Interpretation of the Differences in the Solar Differential Rotation during Even and Odd Sunspot Cycles

Abstract

Using the data on sunspot groups during the period 1879-2004, we have found that the solar equatorial rotation rate during the odd-numbered sunspot cycles is well correlated with the equatorial rotation rate of the preceding even-numbered sunspot cycles, which is similar to the well-known Gnevyshev & Ohl rule (G-O rule) in sunspot activity. This indicates that a 22 yr cycle in the equatorial rotation rate begins in an even-numbered cycle and ends in the following odd-numbered cycle, the same as a solar magnetic cycle (Hale cycle), as inferred from the G-O rule. On the other hand, the latitudinal gradient of the solar rotation during the even-numbered cycles is found to be well correlated with that of the preceding odd-numbered cycles. This result indicates that a 22 yr cycle in the latitudinal gradient begins in an odd-numbered cycle and ends in the following even-numbered cycle. That is, the phase of the beginning of a 22 yr cycle in the latitudinal gradient is different by about 180° relative to the beginning of a 22 yr magnetic cycle.