PREDICTION OF THE INTERPLANETARY MAGNETIC-FIELD STRENGTH

A new model of the coronal and interplanetary magnetic field can predi ct both the interplanetary magnetic field strength and its polarity fr om measurements of the photospheric magnetic field. The model includes the effects of the large-scale horizontal electric currents flowing i n the inner corona, of the warped heliospheric current sheet in the up per corona, and of volume currents flowing in the region where the sol ar wind plasma totally controls the magnetic field. The model matches the MHD solution for a simple dipole test case better than earlier sou rce surface and current sheet models. The strength and polarity of the radial interplanetary magnetic field component predicted for quiet ti me samples in each year from 1977 to 1986 agree with observations made near the Earth's orbit better than the hybrid MHD-source surface mode l (Wang and Sheeley, 1988). The results raise the question of whether coronal holes are the only solar source of the interplanetary magnetic field in the solar wind. If some interplanetary flux originates outsi de coronal holes, the model can match the observed field using the acc epted 1.8 saturation correction factor for lambda 5250 Angstrom magnet ograph observations. Requiring open flux to come exclusively from coro nal holes requires an additional factor of two.