Evidence of a diffuse magnetopause boundary.

Observational evidence is presented to show that the magnetosphere-magnetopause boundary was diffuse during the Pioneer 8 magnetopause traversal on Dec. 14 and 15, 1967. This boundary was characterized by proton fluxes of significantly lower intensity than those observed in the magnetosheath. In addition, the angles of flow associated with the fluxes at the boundary were more diverse than those observed in the magnetosheath. Proton energy spectra are presented to indicate the change in the spectral shape at the boundary. The observational evidence is consistent with calculations by Axford and Dryer of a viscous magnetopause boundary layer, which is a function of an anomalous nonclassical kinematic viscosity. The observational evidence presented for the diffuse magnetosphere boundary may also be consistent with Dungey's model reconnection of magnetic field lines and an open magnetosphere.