A new technique for the mapping of ionospheric field-aligned currents from satellite magnetometer data

Abstract

A new, state of the art technique is being developed for mapping the large-scale, field-aligned currents above the ionosphere. The method uses satellite measurements of the magnetic field, but unlike previous techniques, which have usually relied upon the infinite current sheet assumption, the new method makes no assumption about the current geometry. The new technique is an adaptation of one used with much success to model the electric potential distribution over the polar caps. Previous electric potential maps were derived from measurements of the potential along multiple satellite passes, by using a least-error fit of spherical harmonic coefficients. The models of the currents are derived from similar maps ofmagnetic Euler potential. These Euler potentials are obtained by a path integral of the cross product of a radial vector with the measured magnetic field perturbations. Surface potential maps are derived by a least-error-fit of several paths, and the field-aligned current density is then calculated from the horizontal surface Laplacian of the potential functions. Maps that are derived using this technique show unprecedented details. It is planned that a comprehensive set of field-aligned current maps will be developed for various orientations of the interplanetary magnetic field (IMF).