QUANTITATIVE MAGNETOSPHERE MODELS DERIVED FROM SPACECRAFT MAGNETOMETER DATA

摘要

Quantitative models of the external magnetospheric field have been derived by making least-squares fits to magnetic field measurements from four IMP satellites. The data set consists of 12,616 vector field averages over half-RE intervals between 4 and 17 RE, taken from 451 satellite crbits between 1966 and 1972. The data were fit to a power series expansion in the solar magnetic coordinates and the solar wind-dipole tilt angle, and thus the models contain the effects of seasonal north-south asymmetries. The expansions are divergence-free, but unlike the usual scalar potential expansions, the models contain a non-zero curl representing currents distributed within the magnetosphere. Characteristics of four models are presented, representing different degrees of magnetic disturbance as determined by the range of Kp values. The latitude at the earth separating open polar cap field lines from field lines closing on the dayside is about 5 lower than that determined by previous theoretically-derived models. At times of high Kp, additional high latitude field lines are drawn back into the tail. Near solstice, the separation latitude can be as low as 75 in the winter hemisphere. . The average northward component of the external field it. Much smaller than that predicted by theoretical models, indicating the important effects of distributed currents in the magnetosphere. Current densities implied by the models are of the order of 10-9an-.p/m2 across the magnetotail.