| 其他摘要 | The discovery of solar rotation is closely related to the discovery of sunspots. Early in seventeenth, the solar rotation was observed. The rotation of the pattern of magnetic fields is studied after the continuous record of magnetograms. Solar magnetic fields play an important role in existence and variability of solar activity. Much solar activity seems to be connected with the magnetic fields. In the dynamo theories, the differential rotation provides a mechanism for the conversion of a poloidal magnetic field into a toroidal field. Doing research about the rotation of solar magnetic fields is helpful in understanding the physical process of solar activity. The thesis, which is presented in five chapters, makes a study of the rotation of the photospheric magnetic fields about the rotation profile, the temporal variation and the difference in the rotation of different polarities. In chapter one, a brief introduction about the photospheric magnetic fields, surface magnetic features and the solar rotation relevant to my study is given first. The autocorrelation method and the cross-correlation method, which have been applied to analyze the rotation of the observed pattern of solar magnetic fields, are described and contrasted in detail. Then a review of the present status of the rotation of the photospheric magnetic fields is present, including its latitude-variation, its temporal variation, its north-south asymmetry, as well as its relationship with the strength of magnetic fields. Two different rotation laws, the normal differential rotation profile and the quasi-rigid rotation profile, as well as the possible reasons for the difference between them, are chiefly introduced. At the end of this chapter, the previous study of the rotation of different polarities is reviewed. In chapter two, through a cross-correlation analysis of the Carrington synoptic maps, the sidereal rotation rates of solar magnetic fields between ±60 deg latitudes are investigated. The rotation profile of magnetic fields is obtained: the sidereal rotation rates decrease from the equator to mid-latitude and reach their minimum values of about 13.16 deg/day (13.17 deg/day, sidereal) at 53 deg (54 deg) latitude in the northern (southern) hemisphere, then increase toward higher latitudes. Some possible interpretations are discussed for the resulting rotation profile. In chapter three, the differences in sidereal rotation rates between the positive and negative magnetic fields in the latitude range of ±60 deg are obtained separately. And the time-latitude distribution of the rotation rate differences is shown，which looks like a series of butterfly at low latitudes. For comparison, the time-latitude distribution of longitudinally-averaged photospheric magnetic field strength is shown. And it is concluded that the magnetic fields with leading polarity rotate faster than those with the following polarity at low and middle latitudes of both northern and southern hemispheres. However, at higher latitudes, the magnetic fields with leading polarity do not always rotate faster than those with following polarity. Further more, the relationship between the rotation rate differences and solar magnetic field strength is studied through the correlation analysis. Some possible interpretations are discussed for the resulting correlation coefficients. In chapter four, the rotation of the magnetic fields for the present solar cycle 24 is investigated still through a cross-correlation analysis of the Carrington synoptic maps. The temporal variation of sidereal rotation rates of positive and negative magnetic fields at some latitudes are shown, and it can be found that, at low latitudes, the negative fields generally rotate faster than the positive fields in the northern hemisphere, the positive fields generally rotate faster than the negative fields in the southern hemisphere. The mean rotation profiles of the total, positive and negative magnetic fields in the time interval are also obtained. The mean rotation rates of the positive polarity reach their maximum values at about 9 deg latitude in the southern hemisphere. The mean rotation rates of the negative polarity reach their maximum values at about 6 deg latitude in the northern hemisphere. The mean rotation profile of the total magnetic fields displays an obvious north-south asymmetry that the rotation seems to be more differential in the northern hemisphere. The latitude-variation of the rotation rate difference between positive and negative magnetic fields is further studied, and it is found that the magnetic fields with leading polarity rotate faster than those with the following polarity in each hemisphere, except for the zones around 52 deg latitude of the southern hemisphere and around 35 deg latitude of the northern hemisphere. In the last chapter, a brief summary of this thesis is provided and some unsolved questions about the differential rotation of the photospheric magnetic fields are mentioned. And a forecast for the future related research is put forward. |
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