Property evolution of the shock and the ambient medium. (a): ratios δ (blue) of the standoff distances (Δ) normalized by ROCs and Alfvén Mach numbers, M (pink). The shaded areas denote δ normalized by the minimal and maximal ROCs plus the errors propagated from surface fittings and the errors of M propagated from δ. (b): Alfvén speeds, V_A, for γ = 4/3. The errors of V_A are propagated from M and the shock velocities. The V_A derived by Gopalswamy & Yashiro (2011) (asterisk) and Kim et al. (2012) (diamond) are marked. (c): coronal magnetic field strength, B, for γ = 4/3, calculated using the SDR method. The filled circles represent B derived from the density model of Leblanc et al. (1998). The solid line is the empirical magnetic field model in Dulk & McLean (1978). The B estimated in Kim et al. (2012) and Gopalswamy & Yashiro (2011) are marked by diamonds and asterisks.