Some aspects of geomagnetic disturbances at polar latitudes

At polar latitudes, K-p is not always a good indicator of geomagnetic disturbances. We devise an index K* for one specific station, similar to the K index, which can be calculated automatically. Good correlation is found between K* and K-p, but Sigma K* appears to order the quietest days better than Sigma K-p. Moreover, we find that the daily variance sigma(2) correlates well with K* and K-p, implying that the daily variation amplitude increases when driven by geomagnetic disturbances at these polar latitudes.