Evolution of latitude zonal structure of the large-scale magnetic field in solar cycles

Properties of a latitude zonal component of the large-scale solar magnetic field are analyzed on the basis of H alpha charts for 1905-1982. Poleward migration of prominences is used to determine the time of reversal of the polar magnetic field for 1870-1905. It is shown that, in each hemisphere, the polar, middle-latitude, and equatorial zones of the predominant polarity of a large-scale magnetic field can be detected by calculating the average latitude of the prominence samples referred to one boundary of the large-scale magnetic field. The cases of a single and three-fold polar magnetic field reversal are investigated. It is shown that the prominence samples referred to one boundary of the large-scale magnetic field do not have any regular equatorward drift. They manifest a poleward migration with a variable velocity to 30 m sec super(-) super(1) depending upon the phase of the cycle. The direction of migration is the same for both low- and high-latitude zones. Two different time intervals of poleward migration are found. One lasts from the beginning of the cycle to the time of polar magnetic field reversal, and the other lasts from the time of reversal to the time of minimum activity. The velocity of poleward migration of prominences during the first period is from 5 to 30 m sec super(-) super(1) , and the second period is devoid of regular latitude drift.