Scatter plots of every population member for each parameter. The horizontal purple line denotes 95% of the maximum χ^-2. The central vertical purple line is the optimum value for each parameter, with error bars given by the neighbouring vertical purple lines. The vertical blue lines in the bottom left and middle panels are the values obtained from fitting the velocity profile in Eq. (3) to observational data (see Sect. 4). The bottom right panel shows the optimal meridional flow profile (bold purple) with acceptable profiles represented by the surrounding purple shading.