Top row: radial surface vector field difference between a) modelled B without preprocessing and H_obs, b) modelled B^pre and H_obs, c) initial potential and H_obs. Middle row: latitudinal surface vector field difference between d) modelled B without preprocessing and H_obs, e) modelled B^pre and H_obs, and f) initial potential and H_obs. Bottom row: longitudinal surface vector field difference between g) modelled B without preprocessing and H_obs, h) modelled B^pre and H_obs, and i) initial potential and H_obs. The vertical and horizontal axes show latitude, θ and longitude, φ in degree on the photosphere respectively.