Average position of the Venusian IMB at solar maximum. (a) The altitude of the dayside IMB (marked by black dots) as a function of SZA. The orange asterisks are the median value of these altitudes. The blue curve is the fitted altitude based on the median altitudes. (b) The IMB crossings (black dots), the fitted IMB location (blue line), the IMB location at solar minimum from Zhang et al. (2008a) (red line), and the IMB location at solar maximum from Zhang et al. (1991) (green line). The nightside IMB distance R_VSO is fitted as a function of X_VSO.