An ISEE 3 high time resolution study of interplanetary parameter correlations with magnetospheric activity

Abstract

From 1978 to 1982 the ISEE 3 spacecraft was in a ‘halo’ orbit around the sun‐earth Lagrangian point L1 approximately 240 RE upstream of the earth and was continuously in the upstream solar wind. In order to evaluate the efficacy of such a spacecraft as a real time interplanetary monitor to predict substorm activity and to measure solar wind energy input into the terrestrial magnetosphere, three periods in 1978 were selected in which to perform detailed correlation analyses between solar wind and interplanetary magnetic field (IMF) parameters and magnetospheric activity indices such as AE and Dst. High time resolution (1 min) averages of combined solar wind parameters and IMF parameters were used to perform linear cross‐correlation analyses with the similarly averaged magnetospheric activity indices. A significant dependence of these results on levels of activity is found. During relatively quiet conditions, all tested parameters (ε, VBs, V²Bs) produce high (0.7–0.8), nearly identical linear correlation coefficients with AE. During disturbed times, substantially lower correlations between all parameters and AE are found (r ≲ 0.6 for VBs; r ≲ 0.4 for ε). A measure of total magnetospheric energy dissipation (UT) involving both auroral and ring current terms is useful and can be meaningfully calculated during disturbed periods of geomagnetic storm (or stormlike) activity. UT is rather highly correlated (r > 0.6) with all tested parameters during disturbed times. The parameter ε is often superior to the Bs parameters in prediction of UT. Notably, we find that the typical intrinsic 25‐ to 40‐min delay between interplanetary parameters and magnetospheric response during quiet periods diminishes to ≲15 min during disturbed times.