STRUCTURE AND EVOLUTION OF THE LARGE SCALE SOLAR AND HELIOSPHERIC MAGNETIC FIELDS

The structure and evolution of the large scale photospheric and coronal magnetic fields in the interval 1976 - 1983 have been studied using observations from the Stanford Solar Observatory and a potential field model. The solar wind in the heliosphere is organized into large regions in which the magnetic field has a component either toward or away from the sun. The model predicts the location of the current sheet separating these regions. Near solar minimum, in 1976, the current sheet lay within a few degrees of the solar equator having two extensions north and south of the equator. Soon after minimum the latitudinal extent began to increase. The sheet reached to at least 50 degrees from 1978 through 1983. The complex structure near maximum occasionally included multiple current sheets. Large scale structures persist for up to two years during the entire interval.;During most of the solar cycle the heliospheric field cannot be adequately described as a dipole. For much of the cycle the quadrupole and occasionally octupole moments of the field are more important, especially for the structure in the ecliptic. The complex field configuration near maximum does not correspond to a dipole rotating from north to south as the polar fields change as has been previously suggested. The large latitudinal extent of the current sheet over much of the cycle affects the propagation of cosmic rays. The coronal field does not fully participate in differential rotation, similar to coronal holes. Locations of coronal holes coincide with strong field regions on the source surface. Correlations exist between coronal and photospheric structures but work remains to be done in relating the coronal features to photospheric and deeper lying structures.;To minimize the errors in determining the heliospheric field structure, particular attention has been paid to decreasing the distorting effects of rapid field evolution, finding the optimum source surface radius, determining the correction to the sun's polar field, and handling missing data. The predicted structure agrees with direct interplanetary field measurements taken near the ecliptic and with coronameter and interplanetary scintillation measurements which infer the three dimensional interplanetary magnetic structure.