Abstract.A model of t h e large-scale magnetic f i e l d structure above 2. d sector p a t t e r n i s r e l a t e d t o t h e f i e l d p a t t e r n a t t h i

A quasi‐stationary corotating structure in the interplanetary magnetic field has been observed with the Imp 1 satellite during 3 solar rotations. The interplanetary field is directed predominantly away from the sun for 2/7 of a rotation, then toward the sun for 2/7 of a rotation, then away from the sun for 2/7 of a rotation, and finally toward the sun for 1/7 of a rotation. The interplanetary magnetic field magnitude and the solar wind velocity, density, and flux are discussed with regard to this sector structure. As the structure rotates past the earth once every 27 days it influences geomagnetic activity and cosmic‐ray density. A recurring stream of protons of a few Mev energy is almost entirely contained within one sector. The solar source of the recurring geomagnetic storm of December 2, 1963, is associated with a ghost unipolar magnetic region in the solar photosphere.

On physical grounds it is suggested that the sun's polar field strength near a solar minimum is closely related to the following cycle's solar activity. Four methods of estimating the sun's polar magnetic field strength near solar minimum are employed to provide an estimate of cycle 21's yearly mean sunspot number at solar maximum of 140 ± 20. We think of this estimate as a first order attempt to predict the cycle's activity using one parameter of physical importance based upon dynamo theory.

The structure of the heliospheric magnetic field changes substantially during the 11‐year sunspot cycle. We have calculated its configuration for the period 1976–1982 by using a potential field model, continuing our earlier study near solar minimum in 1976–1977 (Hoeksema et al., 1982). In this paper we concentrate on the structure during the rising phase, maximum, and early decline of sunspot cycle 21, from 1978 to 1982. Early in this interval there are four warps in the current sheet (the boundary between interplanetary magnetic field toward and away from the sun) giving rise to a four‐sector structure in the interplanetary magnetic field observed at earth. The location of the current sheet changes slowly and extends to a heliographic latitude of approximately 50°. Near maximum the structure is much more complex, with the current sheet extending nearly to the poles. Often there are multiple current sheets. As solar activity decreases, the structure simplifies until, in most of 1982, there is a single, simply shaped current sheet corresponding to a two‐sector interplanetary magnetic field structure in the ecliptic plane. The sun's polar fields, not fully measured by magnetographs such as that at the Stanford Solar Observatory, substantially influence the calculated position of the current sheet near sunspot minimum. We have determined the strength of the polar field correction throughout this period and include it in our model calculations. The lower latitude magnetic fields become much stronger as the polar fields weaken and reverse polarity near maximum, decreasing the influence of the polar field correction. The major model parameter is the radius of the source surface, the spherical surface at which the field lines become radial. Correlations of interplanetary magnetic field polarity observed by spacecraft with that predicted by the model calculated at various source surface radii indicate that the optimum source surface radius is not significantly different from 2.5 RS during this part of the solar cycle.

We have investigated solar wind flow properties associated with very low helium to hydrogen abundance ratios (A(He)) observed with Los Alamos instrumentation on IMP 6, 7, and 8 during the 1971 ‐ 1978 interval. A characteristic pattern has been discovered, consisting of correlated interplanetary field reversals, high plasma density, low and nearly identical H+ and He++ bulk velocities, low H+ and He++ kinetic temperatures and minimums in their ratio. A superposed epoch analysis of 74 well defined sector boundary crossings observed during the 1971–1978 interval provides impressive verification of the above correlation, featuring a pronounced minimum in A(He) at the sector boundary passage. Our epoch analysis provides the cleanest pattern of plasma characteristics yet found in the vicinity of the current sheet associated with sector boundaries. Because coronal streamers straddle the current sheet close to the sun, the pattern discovered is the ‘signal’ of a coronal streamer at 1 AU. Our results provide important constraints on models of helium dynamics in coronal streamers and the low speed solar wind.