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Using the earth‐orbiting spacecraft IMP‐8, we have performed a high time‐resolution (2.5‐min) study of the linear cross‐correlations of a quantitative indicator of magnetospheric substorm activity, the auroral electrojet (AE) index, with several interplanetary (IP) parameters. The present study includes all available satellite data (from an eight‐month period) rather than selecting a small number of substorm events, or a relatively small number of chosen days. Prior published studies have suggested that geomagnetic activity is related to a variety of solar wind parameters: solar wind speed (V); north‐south magnetic field component (B z ); total interplanetary magnetic field (IMF) strength (B); and various combinations of these parameters. Very recently, a new parameter, ϵ(= VB² sin 4 ( θ /2)ℓ o ²), has been suggested as a superior predictor of substorm activity. The other major preferred correlator with geomagnetic activity is VB s , where B s is the southward (B z < 0) component of the IMF. Substantial discussion has ensued as to which parameter is the "best" predictor of substorm activity. The present non‐selective, high‐resolution analysis reveals that VB s generally reaches a higher peak correlation than ϵ (0.6 vs 0.54). Both parameters reach a peak correlation at the same lag time (with AE lagging the IP parameters by ∼40 min.), but VB s also appears to have a preferable qualitative lag profile shape for AE prediction purposes.
Baker et al. (Sun,) studied this question.