Solar cycle dependence of spatial correlation in the solar wind

We investigate the spatial correlation properties of the solar wind using simultaneous observations by the ACE and WIND spacecraft. We use mutual information as a nonlinear measure of correlation and compare this to linear correlation. We find that the correlation lengthscales of fluctuations in density and magnetic field magnitude vary strongly with the solar cycle, whereas correlation lengths of fluctuations in B field components do not. We find the correlation length of |B| ~ 120 Re at solar minimum and ~ 270 Re at maximum and the correlation length of density ~ 75 Re at minimum and ~ 170 Re at minimum. The components of the B field have correlation lengths ~ correlation length |B| at minimum.