Applied Research Corporation, Landover, Maryland

This paper presents observations of the radial and latitudinal variations of the interplanetary magnetic field measured by the Voyager 1 (V1) and Voyager 2 (V2) spacecraft from mid-1977 to mid-1985. The data extend from 1 to 20 AU and from -5° to 26° in heliographic latitude. Data obtained at 1 AU are used to separate temporal variations from radial variations, and plasma measurements from V2 are used to consider the effect of temporal variations in the bulk speed. Observations of the radial variation of the large-scale magnetic field strength in the ecliptic agree with the predictions of Parker's model when temporal variations in the magnetic field and bulk speed are taken into account. The latitudinal variation of the magnetic field observed by V1 is in agreement with the predictions of Parker's model to first approximation. The magnetic field strength at higher latitudes is somewhat lower than expected on the basis of observations made in the ecliptic, but this could be due to an increase in bulk speed and/or a decrease of solar magnetic field strength with latitude. Fluctuations in the strength of the magnetic field are small compared to the large-scale field itself, and they decrease in amplitude with increasing distance approximately as R^-1/4. Fluctuations in the components are relatively large, and they make a significant contribution to the mean field that is not described by Parker's model.

J. Geophys. Res., 92, No. A9, 9885-9892, Sept. 1987