HR: 1330h
AN: SH13A-01    [Abstracts]
TI: Conical Current Sheets in a Source-Surface Model of the Heliosphere
AU: * Schulz, M
EM: mike.schulz@lmco.com
AF: Lockheed Martin Adv Tech Ctr, Dept ADCS, Bldg 255, 3251 Hanover Street, Palo Alto, CA 94304 United States
AB: Different methods of modeling the coronal and heliospheric magnetic field are conveniently visualized and intercompared by applying them to idealized axisymmetric field models. Thus, for example, a dipolar B field with its moment parallel to the Sun's rotation axis leads to a flat heliospheric current sheet. More general solar B fields (still axisymmetric about the solar rotation axis for simplicity) typically lead to cone-shaped current sheets beyond the source surface (and presumably also in MHD models). As in the dipolar case [Schulz et al., Solar Phys., 60, 83-104, 1978], such conical current sheets can be made realistically thin by taking the source surface to be non-spherical in a way that reflects the underlying structure of the Sun's B field. A source surface that seems to work well in this respect [Schulz, Ann. Geophysicae, 15, 1379-1387, 1997] is a surface of constant F = r^-kB, where B is the scalar strength of the Sun's main magnetic field and k (~ 1.4) is a shape parameter. This construction tends to flatten the source surface in regions where B is relatively weak. Thus, for example, the source surface for a dipolar B field is shaped somewhat like a Rugby football, whereas the source surface for an axisymmetric quadrupolar B field is similarly elongated but somewhat flattened (as if stuffed into a cone) at mid-latitudes. A linear combination of co-axial dipolar and quadrupolar B fields generates a somewhat pear-shaped source surface. If the region surrounded by the source surface is regarded as current-free, then the source surface itself should be (as nearly as possible) an equipotential surface for the corresponding magnetic scalar potential (expanded, for example, in spherical harmonics). The solar wind should then flow not quite radially, but rather in a straight line along the outward normal to the source surface, and the heliospheric B field should follow a corresponding generalization of Parker's spiral [Levine et al., Solar Phys., 77, 363-392, 1982]. In particular, heliospheric current sheets (of which there are two if the underlying solar B field is mainly quadrupolar) should emanate from neutral lines on the corresponding source surface. However, because the source surface is relatively flattened in regions where such neutral lines tend to appear, the radial component of the heliospheric B field at r ~ 1 AU and beyond is much more nearly latitude-independent in absolute value than one would expect from models based on a spherical source surface.
DE: 2134 Interplanetary magnetic fields
DE: 2169 Sources of the solar wind
DE: 7509 Corona
DE: 7511 Coronal holes
DE: 7524 Magnetic fields
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2005 Joint Assembly