The latitudinal structure of the heliospheric current sheet during solar activity cycles 21 and 22

Source surface heliomagnetograms from the Wilcox Solar Observatory from 1976 to 1994 were used to determine the evolution of the heliospheric current sheet (HCS) latitudinal extent during solar cycles 21 and 22. We divided the data into four periods, two during the ascending (1976–1978, 1987–1989) and two during the descending phases (1982–84, 1991–94) of the activity cycles. Time intervals near solar maximum activity when the HCS cannot be uniquely determined for every day were not included. We observed a marked difference in the HCS temporal evolution for the ascending and descending periods. A different latitudinal distribution is also present in all four intervals used. For the descending phases of the cycles analysed a two-sector structure is clearly predominant, whereas for one of the ascending phases (1976–1978) a four-sector structure is more prominent. Results clearly demonstrate that the evolution of the HCS is far from being uniform during consecutive cycles, nor is it the same before and after the polar field reversals.