Spectral slopes of the magnetic field in Alfvén unit (top left), velocity (top right), outward Elsässer variable (bottom left), and inward Elsässer variable (bottom right) as functions of the radial solar wind speed V_r and radial distance to the Sun R. The data points were binned according to V_r and R, and the median value inside each bin was calculated, which is reflected in the colors and written in the plot. The bracketed numbers in the plots are the number of data points inside each bin. Bins with no more than 15 data points were discarded.