The solar wind in the outer heliosphere

Abstract

We review recent plasma and magnetic field results stemming from Voyager 1 and 2 observations of the solar wind in the outer heliosphere. The solar wind speed profiles in 2002 are dominated by shock-related speed increases followed by long ramps of decreasing speed. Significant variability in the density and temperature are seen on all time scales. Transient events near solar maxima drive the formation of MIRs which are increasingly important at large radial distances. Both the density and magnetic field magnitude are consistent with the predictions of Parker's solar wind model. The solar wind pressure changes at all latitudes over the solar cycle, resulting in an oscillation of the heliospheric boundary positions. As the Voyagers move farther out, the effect of the interstellar medium on the solar wind increases. Observed speeds at Voyager 2 are about 60 km/s lower than those in the inner heliosphere due to interaction with the interstellar neutrals.