Comparison of the solar wind energy input to the magnetosphere measured byWind and Interball-1

Timely solar wind measurements are indispensable for space weather forecast s and magnetospheric studies, but solar wind variations detected by a dista nt spacecraft might be different from those actually hitting Earth's magnet osphere. To determine how important these differences can be for geophysica l applications, we compared energy input to the magnetosphere which was sim ultaneously measured by the Wind and Interball-1 spacecraft at various dist ances from the Earth. The percentage of equal (with differences less than 1 5%) measurements was found to increase from 30% at energies associated with small substorms to 100% for storm-level energies. The degree of tho spacec raft separation along the X GSE coordinate and in the YZ GSE plane appeared to be of minor importance within the limits of Wind and Interball-1 orbits . (C) 2001 Elsevier Science Ltd. All rights reserved.