Significance of the high-latitude geomagnetic index AES-80: comparison with the PC index

A new index AES-80 was derived in order to provide a measure of the geomagnetic activity at high southern latitudes (Ballatore et al., 1998). The comparison between the southern hemisphere AES-80 with the northern hemisphere PC index is reported here for the period May 1994–April 1995. It is found that during southward IMF the two parameters record the geomagnetic disturbances rather similarly. In contrast, during northward IMF, only AES-80 is capable of recording geomagnetic activity occurring in the nominal polar cap region. In agreement with this finding, a slightly higher correlation coefficient is found between AES-80 and PC during southward IMF than during the northward IMF condition. Although at any time the two indices reflect opposite seasons, the overall correlations found between the two indices are significant, independent of the specific UT interval considered. The UT modulation (which should possibly be taken into account in the use of the indices) has been calculated for the AES-80 and the PC index. The results show that, for the specific period considered, the PC index dependence on UT is more significant than that of the AES-80 parameter.