The coronal and interplanetary current sheet in early 1976

A comparison of Helios 1 and 2 observations of the interplanetary sector pattern in early 1976 with the maximum brightness curves in the K coronameter data at 1.5 R S shows that the latter may be identified with the footprints of the sector boundary surface to an accuracy of ≈ 10°. The neutral line computed by Wilcox et al (1980) from a potential field model, using Mt. Wilson photospheric magnetic field measurements and a source surface at 2.6 R S , is similar in shape to the K coronameter maximum brightness curves but extends to higher latitudes. The Helios observations give better agreement with the K coronameter curves for the one solar rotation on which a test of the latitutude extent of the neutral line was possible. The K coronameter results and the Helios data show that the sector boundary surface probably extended to ≈ 15° in the northern hemisphere and to ≈ 30° in the southern hemisphere, with little change between 1.5 R S and 1 AU. The surface was warped appreciably from a single tilted plane (a dipole configuration) suggesting a significant magnetic quadrupole contribution.