Plot of the measured parameter ﹩C^{2}_{N}﹩ as a function of heliocentric distance r. The units of ﹩C^{2}_{N}﹩ are ﹩\mathrm{m}\,^{-20/ 3}﹩. Each point represents a measurement of a different radio source observed at a specific solar elongation. The solid line represents a model for ﹩C^{2}_{N}﹩ from prior observations (eq. [4]). The flanking dashed lines represent a factor of 3 scatter above and below this relationship due to natural variability in the solar wind.