Rocket-based magnetic observations of auroral birkeland currents in association with a structured auroral arc

A rocket-borne experiment package containing a vector magnetometer and an array of charged particle detectors was launched over a structured auroral arc from Poker Flat, Alaska, at 0722 UT on February 25, 1972. This paper discusses the results of the magnetometer data which indicate the existence of a pair of oppositely directed Birkeland current sheets with magnitudes of ∼2.7 × 10−5 A/m² and a system of two eastward electrojets. The downward Birkeland current flowed to the south of the upward current which coincided with the location of the peak auroral luminosity and the region of maximum electron precipitation as measured by the on-board particle detectors. Some changes in the magnetic field profile during the flight are interpreted as being due to movement of the sheet currents in range and azimuth corresponding to the motion of two large folds in the arc as determined from the all-sky camera pictures.