Comparison between indices during geomagnetic disturbances

Auroral indices AE, AU, AL, and Troshichev index from Thule, PC (Polar Cap) are compared for geomagnetic disturbances of different intensities. To identify perturbations, the indices Dst and AE have been used. Fourteen storms have been analyzed, with Dst index minimum value between –50 nT and –600 nT (86% of them are great storms). The correlation coefficient, r, between AE and PC is above 0.65 for all storms analyzed. For AL index the correlation values are close to those of AE; but r is low for AU index. Thirty-five substorms were identified, with AE maximum values between 271 nT and 2218 nT. Eighty-one percent of them have a correlation coefficient between AE and PC above 0.6 and 47% above 0.8. The values obtained do not depend on disturbance intensity. The results suggest that PC index can be used as a fast indicator of global magnetic activity in the auroral oval even during great disturbances.