Solar Cycle Variations of Coronal Neutral Lines and Polar Regions Activity

摘要

Observations of the corona, of prominences, of polar faculae and of large scale magnetic fields show solar activity over all latitudes, in contrast with sunspot activity, which is limited to mid-latitudes. The global behavior of the solar activity is considered here thanks to the analysis of chromospheric synoptic maps which include the location of Ha and Ca II k prominences. The process of migration of neutral lines during the cycle (supposed to represent the large scale coronal magnetic field) is shown. After subsequent averaging of the maps, a discrete number of latitude zones is found: not more than 10, the most probable number being 3 or 5. This suggests the occurrence of dominant modes (1=3 and 1=5) of the large scale coronal magnetic field and inferred coronal structures for different epochs of the solar cycle. The geoactivity of coronal streamers could be related to the modes, noticing the dipole (1=1) mode is almost absent. A more detailed analysis points to the importance of the poleward migration of neutral lines (with v = 5 to 40 micro sec-1). The non-symmetric behavior of the N and S hemisphere as well as the erratic behavior of the corresponding sunspot activity in each hemisphere is emphasized which reflects the behavior of both the radial component and the toroidal component of the field. Reprints. (jhd)