Dependence of IMB altitude on the solar activity and on the solar wind parameters. (a) The extrapolated terminator IMB altitudes Alt_ter (black points) distribute with the sunspot number (SSN) observed from the Earth. A linear regression (black line) was done to all of the data points. The mean Alt_ter in SSN bins of 5 Counts (green dots), the standard deviation in each bin (thin red error bars), and the standard error of the mean (thick red error bars) are shown. (b–d) Similar to (a), but the Alt_ter was normalized to the average SSN and is referred as the “IMB altitude.” There is no correlation between the IMB altitude and the solar wind velocity (P-value > 0.01).