J. -L. Xie, X. -J. Shi, J. -C. Xu
The daily sunspot numbers of the whole disk as well as the northern and
southern hemispheres from January 1, 1945 to December 31, 2010 are used to
investigate the temporal variation of the rotational cycle length through the
continuous wavelet transformation analysis method. The auto-correlation
function analysis of daily hemispheric sunspot numbers shows that the southern
hemisphere rotates faster than the northern hemisphere. The results obtained
from the wavelet transformation analysis are: there exists no direct
relationship between the variation trend of the rotational cycle length and the
variation trend of solar activity in the two hemispheres; the rotational cycle
length of both hemispheres has no significant period appearing at the 11 years,
but has significant period of about 7.6 years. Analysis concerning the solar
cycle dependence of the rotational cycle length shows that in the whole disk
and the northern hemisphere acceleration seems to appear before the minimum
time of solar activity. Furthermore, the cross-correlation study indicates that
the rotational cycle length of the two hemispheres has different phases, and
the rotational cycle length of the whole disk as well as the northern and
southern hemispheres also has phase shifts with the corresponding solar
activity. What's more, the temporal variation of North-South (N-S) asymmetry of
the rotational cycle length is also studied; it displays the same variation
trend as the N-S asymmetry of solar activity in a solar cycle as well as in the
considered time interval, and it has two significant periods of 7.7 and 17.5
years. Moreover, the N-S asymmetry of the rotational cycle length and the N-S
asymmetry of solar activity are highly correlated. It's inferred that the
northern hemisphere should rotate faster at the beginning of solar cycle 24.
View original:
http://arxiv.org/abs/1112.1578
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