AN ANALYTIC SOLAR MAGNETIC-FIELD MODEL

We describe a simple analytic model for the magnetic field in the sola r corona and interplanetary space which is appropriate to solar minimu m conditions. The model combines an azimuthal current sheet in the equ atorial plane with an axisymmetric multipole field representing the in ternal magnetic field of the Sun. The radial component of the field fi lling interplanetary space is approximately monopolar at large helioce ntric distances as observed. These open field lines connect to the pol ar regions of the Sun and define the polar coronal holes which are pre valent at solar minimum and which are the source of the fast solar win d. By including both dipole and a quadrupole terms at the origin it is possible to construct a good representation of the coronal magnetic f ield in such conditions. We also note that the Parker spiral will be u nderwound relative to the case of the monopole because the open field Lines emanate from solar latitudes in excess of 60 degrees.