MLAT difference between T89 and (T96, T01, T04, TA15b, and TA15n) against the r_GSM position of the BBF. The color scale represents the ratio of the normalized Hp30 geomagnetic index (input parameter in T89) to the normalized input parameters with the highest correlation (E_KLV, Sym-h, W₁, B-index, and N-index for T96, T01, T04, TA15b, and TA15n, respectively). The solid black line indicates the mean value. Normalization was performed using the median value.