Coronal and interplanetary magnetic field models

Abstract

We provide an historical perspective of coronal and interplanetary field models. The structure of the interplanetary medium is controlled by the coronal magnetic field from which the solar wind emanates. This field has been described with “Source Surface” (SS) and “Heliospheric Current Sheet” (HCS) models. The “Source Surface” model was the first to open the solar field into interplanetary space using volumetric coronal currents, which were a “source” for the IMF. The Heliospheric Current Sheet (HCS) model provided a more physically realistic solution. The field structure was primarily a dipole, however, without regard to sign, the shape appeared to be a monopole pattern (uniform field stress). Ulysses has observed this behavior. Recently, Sheeley and Wang have utilized the HCS field model to calculate solar wind structures fairly accurately. Fisk, Schwadron, and Zurbuchen have investigated small differences from the SS model. These differences allow field line motions reminiscent of a “timeline” or moving “streakline” in a flow field, similar to the smoke pattern generated by a skywriting plane. Differences exist in the magnetic field geometry, from the Parker “garden hose” model affecting both the “winding angle” as well as the amount of latitudinal “wandering.”