Rocket-based measurement of particle fluxes and currents in an auroral arc

A rocket-borne auroral particles experiment was fired from Fort Churchill, Canada, over a homogeneous arc at 2000 local time on February 26, 1969. Detectors measured the pitch-angle distribution of the fluxes of electrons with energies of 2–18 and <50 kev, and of protons with energies of 2–18 and 80–1000 kev. The downward (zero pitch angle) electron flux in the 2- to 18-kev interval reached ∼3×108/cm2 sec ster kev as the rocket passed over the visible arc at 135 km altitude. The total backscattered flux was about 20% of the downward flux in the same energy range. No protons in the 2- to 18-kev range, or any higher energy particles, were found in significant quantities. The north-to-south electron flux profile of the arc was roughly gaussian with a 10% intensity width of 10 km and a smaller secondary maximum to the north of the central maximum. Integration of the electron flux over pitch angle showed that the maximum net current density due to 2- to 18-kev electrons was 1.5×10−5 amp/m2. The current density integrated across the arc width was equivalent to a sheet current of 0.08 amp/m. A vector magnetometer aboard the rocket indicated an upward current of 0.16 amp/m in the region of the downward electron flux. Comparison of these measurements shows that the energetic (>2 kev) auroral electrons carry a substantial part of the Birkeland current. The intensity and location of the electron fluxes were in reasonable agreement with measurements by ground-based photometers and all-sky cameras. The arc extended at least 1500 km in an east-west direction and was not associated with substorm activity.