Sensing global Birkeland currents with Iridium (R) engineering magnetometer data

The Iridium system consists of >70 satellites in low altitude, 780km, polar orbits in six equally spaced orbit planes with at least eleven satellites in each plane. Each satellite carries an engineering magnetometer with 48nT resolution. Techniques have been developed at JHU/APL to process Iridium m agnetic field data and obtain global maps of magnetic perturbations due to field aligned currents (FACs). The noise level in the processed data is typ ically 70 to 100 nT and readings above the noise level occur at high magnet ic latitudes consistent with an auroral signature. Time series also display well known features characteristic of FACs. Synoptic maps derived using th ree hours of data from 17 February, 2000, AE similar to 100-300nT, show pat terns consistent with the Region 1/2 currents previously determined statist ically. The Iridium data set provides new global measurements of the Birkel and currents in both hemispheres on time scales of a few hours or less.