Scheme of the algorithm to obtain effective energy of each proton channel by comparison with the two sets of GLE modelling. The solid and dash curves are converted differential spectra from rigidity to kinetic energy, based on the two fitting functions for the 2005-01-20 GLE, respectively, and symbols are fluences of GOES 11 proton channel P2–P11 for this event, calculated by subtracting background fluxes at different times (1 day and 7 days before the onset). The two crossed straight lines demonstrate the scheme to estimate the effective energy for P9. The horizontal line marks the measured fluence level. The vertical line indicates the effective energy at which the fluence best matches the MBF fitting of this event.