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Long-term Variations of Solar Differential Rotation  

K. J. Li   Submitted: 2012-05-08 18:17

Long-term variations of solar differential rotation and sunspot activity are investigated through re-analyzing the data on parameters of the differential rotation law obtained by Makarov, Tlatov, and Callebaut (1997), Javaraiah, Bertello, and Ulrich (2005a, b), and Javaraiah et al. (2009). Our results indicate that the solar surface rotation rate at the Equator (indicated by the A parameter of the standard solar rotation law) shows a secular decrease since cycle 12 onwards, given by about 1,-,1.5 imes10-3(deg day-1 year-1). The B parameter of the standard differential rotation law seems to also show a secular decrease since cycle 12 onwards, but of weak statistical significance. The rotation rate averaged on latitudes (0o,-,40o) does not show a secular trend of statistical significance. Moreover, the average sunspot area shows a secular increase of statistical significance since cycle 12 onwards, while a negative correlation is found between the level of sunspot activity (indicated by the average sunspot area) and the solar equatorial rotation in the long run.

Authors: K.J. Li, W. Feng, X.J. Shi, J.L. Xie, P.X. Gao, H.F. Liang
Projects: None

Publication Status: Accepted by Solar Phys.
Last Modified: 2012-05-09 12:09
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The cyclic behavior of solar full-disk activity  

K. J. Li   Submitted: 2008-07-02 18:03

In order to describe the cyclic behavior of solar full-disk activity (the surface magnetic fields, filaments, the green (Fe XIV, 5303AA) corona local maxima intensities, and torsional oscillations), we propose a new concept, a 'full-disk activity cycle', which consists of two successive normal cycles: a high-latitude activity cycle following a low-latitude activity cycle. When solar activity begins to progress into a full-disk activity cycle, it latitudinally rushes to the poles, starting from middle latitudes (about 400) at about a normal cycle minimum. At the solar poles, magnetic polarity reversal takes place on both the solar hemispheres, and opposite reversals occur on the opposite hemispheres, resultingly, the new appearing magnetic polarity at high latitudes on a hemisphere will become the leading magnetic polarity of regions at low latitudes on the same hemisphere in the following normal cycle. After that the latitudinal drift of solar activity reaches the solar poles at about the maximum time of the normal cycle, solar activity begins to latitudinally migrate in a reverse direction; it moves toward the equator continually till almost arriving at the solar equator and lasting for about 1.5 normal cycles. When a full-disk activity cycle progresses from a high-latitude activity cycle into a low-latitude activity cycle, the next full-disk activity cycle begins. Two successive full-disk activity cycles have a normal cycle overlapped in time, but are spatially separated. The characteristics of full-disk activity cycles are summarized as well. At present we do not know why a full-disk activity cycle begins at mid-latitudes, it is perhaps related with solar differential rotation, further work is required to uncover the physical mechanisms behind the concept.

Authors: K. J. Li, Q. X. Li, P X. Gao, and X. J. Shi
Projects: None

Publication Status: JGR Space Physics (accepted)
Last Modified: 2008-09-23 20:57
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Long-term Variations of Solar Differential Rotation
The cyclic behavior of solar full-disk activity

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