Synoptic global tendencies of solar background magnetic fields at the 19th cycle

Abstract

On the basis of H synoptic maps of background magnetic fields for the 19th cycle, we take one map for every ten rotations and in a continuous manner for the maximum of the cycle, where we take for the analysis all maps within the maximum of the cycle. We constructed tendential polynomial surfaces to represent the field that is proportional to the positive magnetic flux. It is shown that with the polynomial surfaces of fust degree it is always possible to represent the field, except for the map immediately precedink the process of polarities' inversion at the Sun. In addition. the "surface gradient" of that magnitude shows that inversion of polarities at the Sun as a whole occurs earlier (13 rotations) than the onset of the change of polarities at the Sun's poles. Maps whose tendential surfaces improve with increasing order of the surface are those at the beginning. at maximum and immediately aftei' maximum of the cycle. In particular. the two only maps whose representation becomes better with a surface of fourth degree or more occur at the beginning of the cycle and at the medium phase of the cycle. In those maps, the ribbons proportional to ilet flux equal to zero are antisymmetric.