Inference of magnetospheric currents from multipoint magnetic field measurements

Abstract

The European Space Agency has deployed four essentially identical spacecraft into similar near-polar eccentric orbits about the Earth. Each of the four spacecraft carries dual three-axis magnetometers. From simultaneous observations of the magnetic field B at the four vertices of the tetrahedral cluster of spacecraft, it is possible to determine ∇ ×B and then by Ampere's law, the local electrical current density J within the plasma of the Earth's magnetosphere. The purpose of this paper is to illustrate the basic principles of this "curlometer" technique.