Solar magnetic butterfly diagrams of the radial field (B_r) from MDI and GONG data. (a) Smoothed butterfly diagram of B_r, constructed from Carrington maps and combined datasets from SOHO/MDI and GONG. (b) Resolution-downgraded butterfly diagram, with latitudinal resolution reduced to match our observations of ι Hor (10° per pixel). (c) Field-weighted butterfly diagram. The location of each polarity is indicated, with error bars representing the standard deviation of field-strength-weighted latitudes. Linear fits with the corresponding speeds are indicated.