On Evolution of the Photospheric Magnetic Fields on the Sun: Separation of Active/Dissipative/Background Fields by Optimum Thresholds

The distribution of the magnetic flux in the Sun's photosphere is studied using NSO/Kitt Peak Carrington rotation maps of the magnetic flux in the period from 1975 to 2003. In principle it is possible to separate the magnetic fields using these magnetic data into three types: background fields, dissipative fields coming from the active regions and the active region fields themselves. This contribution discusses determination of the optimum thresholds for such separations of the magnetic fields. The threshold between background fields and dissipative fields is derived from the average minimal values of the magnetic flux measured in high latitudes where/when no active region flux and only minimum of the dissipative flux are detected. It's value is 2.8 Gauss. Contrary it is presented that there is no common value of the threshold between the dissipative fields and the active regions fields valid for the whole period under study. It is shown that value of this threshold is in fact unique not only for each Carrington rotation map but that it is specific even for each particular active region. Usually accepted value of 25 Gauss seems to be only the minimal limit of this threshold. Its maximal limit is exceeding value of 110 Gauss. Nevertheless just separation between the background fields and the sum of the dissipative and the active region fields allows to discuss the temporal and latitudinal behaviour of these two types of the magnetic fields during evolution of the solar cycles.

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