Rocket measurements of auroral electric and magnetic fields

A series of five Nike Tomahawk sounding rockets were launched from Fort Churchill into a variety of auroral conditions. Payload instrumentation included electric field meters, magnetometers, auroral photometers, and charged-particle detectors. Horizontal dc electric fields were measured and were found to point southward during negative magnetic bays. This is consistent with the presence of westward-flowing Hall currents. The relative absence of electric-field variations with altitude indicates that field mapping along nearly equipotential magnetic field lines may be taking place. Perturbations measured by the rocket magnetometers and photometers suggest that the auroral electrojet often flows parallel to visible auroral forms and is comprised of a series of thin current filaments of varying intensity. According to the magnetometer records, horizontal electrojet currents of 104 to 106 amp existed during periods of visible auroral activity. An upper limit for a field-aligned current in a zenith auroral display 10 km from the payload was calculated to be 2.5×105 amp on the basis of flux-gate magnetometer data. Results from a solid-state particle detector, however, suggest that the current was probably of much smaller magnitude. Calculations using various current models indicate that it is often necessary to propose the existence of two or more horizontal current filaments to produce agreement between ground-station and rocket magnetic records.