Comparison between the polar cap index, PC, and the auroral electrojet indices AE, AL, and AU

Abstract

The newly introduced index PC for magnetic activity in the polar cap has been examined to establish to which extent it can serve as an indicator of auroral electrojet activity. PC is derived from a single nearpole station, as a 15‐min average index. We have derived it for two stations, one in the northern hemisphere (Thule) and one in the southern hemisphere (Vostok). The simplicity of the PC index enables us to make a large data base for statistical investigations. We have thus used 7 years of PC values for the two stations to analyze the relationship between PC and the auroral zone indices AE, AU, and AL statistically. We find a very high correlation between PC and AE during winter and equinox, the linear correlation coefficient being ≈0.8–0.9 for Thule and ≈0.7–0.8 for Vostok. During summer the correlation is less because the PC index is then disturbed by polar cap currents controlled by the northward and east‐west components of the interplanetary magnetic field. We therefore stress the importance of having PC available from both the northern and southern hemisphere. From event studies we find that PC is sensitive both to DP 2 type electrojet activity and to substorm intensifications of the westward electrojet in the midnight or postmidnight sector but less sensitive to substorm intensifications of the westward electrojet in the premidnight sector. We conclude that PC can serve as a fast available indicator of DP 2 and DP 1 activity in the polar regions, excluding intrusions of the westward electrojet in the premidnight sector.

On the Usage of Geomagnetic Indices for Data Selection in Internal Field Modelling

“…So all these indices seem to pick weak AL activity with higher probability than the condition of √ M P B being ∼ 10 nT. The best correspondence appears to be between P C and AL, which is consistent with the results of Vennerstrøm et al (1991) who report high correlation values (0.8-0.9) between P CN and AE particularly during winter and equinox times. Fig.…”

A relation between the locations of the polar boundary of outer electron radiation belt and the equatorial boundary of the auroral oval

“…Comparing Fig. 4 and 5, we can see that both distributions are very similar, which 10 can be explained by high correlation between the AE and PC indexes obtained by Vennerstrøm et al (1991). This correlation is related to the formation of ionospheric current systems as a result of the magnetosphere-ionosphere interactions, and the dominant role of the Region 1 currents of Iijima and Potemra (1976) in the formation of the PC index (Troshichev and Janzhura, 2012).…”

A new southern high-latitude index

“…Some relationship between these two indices is expected, at least because the ®eld-aligned currents at the poleward auroral rim both in¯uence geomagnetic perturbations at polar latitudes and feed the ionospheric auroral electrojets. A good correlation between the PC and AE indices has, in fact, been reported by Vennerstrùm et al (1991).…”

“…Although a good correlation between PC and AE was found by Vennerstrùm et al (1991), they also noted that, when the auroral oval is shifted poleward, substorms occurring in those high latitudes were too weak and localized to be detected by the PC index.…”