Large-scale structure of the heliospheric magnetic field - 1976-1991

A uniform set of computed large-scale coronal fields derived from photospheric field observations now exists for the interval 1976 to the present. Using this data base we can begin to compare Solar Cycle 21 with Solar Cycle 22. The character of the field and its evolution are the same, but many of the particulars are different. The polar field was about 25 percent stronger at solar minimum in 1986 than in 1976, consequently the heliospheric current sheet was confined to a narrower latitude range. In the rising phase of Cycle 21 a strong 4-sector pattern developed; the same pattern was not present in Cycle 22. Other differences include the timing of the polar field reversals and changes in latitudinal extent of the current sheet.