NASA Goddard Space Flight Center, Laboratory for Extraterrestrial Physics, Greenbelt, Maryland 20771

We discuss Voyager 1 (V1) observations of the heliospheric magnetic field strength from 1978 through 1996. During this period the distance of V1 from the Sun increased from » 3 AU to 66 AU and its heliographic latitude increased from » 5° S to 33° N. The magnetic field strength profile observed by V1 is consistent with Parker's spiral field model when one considers (1) the solar cycle variation of the observed magnetic field strength at 1 AU, B₁(t) (which is a measure of the source field strength) and (2) the latitudinal and solar cycle variations of the solar wind speed V(t, q ). Both B₁(t) and V(t, q ) make significant contributions to the variation of the magnetic field strength variations observed by V1. There is no evidence for a "magnetic flux deficit" increasing with distance from the Sun. There is a solar cycle variation of the magnetic field strength in the outer heliosphere, which will affect the modulation of cosmic rays.

J. Geophys. Res., 103, No. A10, 23727-23732, Oct. 1998