Comparison of the dynamics of the AU and PC indices

The properties of AU and PC data were analyzed with different methods. It is shown that the dynamical behavior of the AU and PC time series, as analyzed by the structure function (SF), are very similar, while the SF of the AL time series shows different behavior. The SF of the AL data has a slope of 0.5 up to about 2 hours, after which it quickly decreases to about 0.1. On the other hand the slope of the SFs of AU and PC data continuously decreases to about 0.2, and in a longer time scale. It is suggested that the dissipative auroral electrojet currents have a characteristic time scale of 2 hours, and this underlies the AL dynamics. In contrast with this, the nondissipative Hall currents that most influence the AU and PC dynamics, do not seem to have a distinct characteristic time scale. However, the crosscorrelation between the PC and AL indices is higher than that of the PC and AU indices, especially during wintertime. This is argued to result from the polar cap currents being more interconnected with the westward electrojets than with the eastward electrojets, in spite of the difference in their dynamic behaviors.