Regularities of variation of the heliospheric current sheet orientation during the solar activity cycle

Evolution of spatial orientation of the heliospheric current sheet (HCS) has been studied in detail using synoptic maps of the HCS configuration over the period 1971–1989. Analysis involves all phases of the sunspot cycle except for two years of maximum solar activity. The helmet-like coronal streamers are confirmed to be structural elements of the HCS. The r.m.s. deviation of a real HCS configuration from a plane does not exceed about 10° during most of the sunspot cycle length. Hence, minimum-type corona should be observed every time the HCS is oriented parallel to the line-of-sight, independent of the cycle phase. Such occasions have been observed apart from the sunspot minimum epochs at the solar eclipses of 31 August, 1932 and 11 July, 1991.Regularities of variation of the two following parameters of the HCS orientation have been revealed: obliquity to the solar equator plane (heel or tilt) and longitudinal orientation (yawing). Behaviour of the above parameters is repeated in different cycles. However, heeling and yawing occur probably not synchronous but rather independent of one another.