Global structure and dynamics of large‐scale fluctuations in the solar wind: Voyager 2 observations during 2005 and 2006

The Voyager 2 (V2) observations of daily averages of the solar wind during 2005 and 2006 from 75.3 AU to 81.6 AU between ≈25.7°S and 27.1°S show both a step‐like trend in the speed V(t) and “large‐scale fluctuations” of the magnetic field strength B, speed V, density N and temperature T. The distribution functions of B, N, and NV2observed by V2 are lognormal and that of V is approximately Gaussian. We introduce a method for specifying the boundary conditions at all latitudes (except near the poles) on a Sun‐centered surface of radius of 1 AU, based on solar magnetic field observations. This paper uses only the boundary conditions at the latitude of V2 and a 1‐D time‐dependent MHD model to calculate the radial evolution of the large‐scale fluctuations of B(t), V(t) and N(t) at distances between 1 and 90 AU. This model explains the V2 observations of a lognormal distribution of B and the Gaussian distribution of V, but not the observed lognormal distributions of N and NV2. The lognormal distribution of B observed by V2 was produced primarily by dynamical processes beyond 1 AU.