Correlation of cusp latitude with Bz and AE (12) using nearly one year's data

This investigation reports the statistical correlation of cusp latitude with the interplanetary magnetic field (IMF) Bz and the AE (12) index. Eleven months of data from 1979 were collected, subject only to the criteria that the IMP 8 spacecraft be outside the magnetopause to measure the IMF and that the daily average of AE (12) exceed 200 nT. In general, the latitudes of the poleward cusp boundaries display higher correlation coefficients than do the latitudes of the equatorward boundaries. The best correlations of cusp latitudes with AE involve no time delay, while the best correlations with Bz involve a 30‐min time delay. The strongest correlation (R = 0.77) occurs between the 30‐min time‐delayed Bz and the latitude of the poleward cusp boundary. The latitude of the equatorward cusp boundary correlates best with the time‐retarded southward Bz (R = 0.75). The best correlations of the cusp latitudes with AE (R = 0.68–0.71) are generally not as good as those with the time‐delayed Bz.