Observations of the neutral atmosphere between 100 and 200 km using ARIA rocket‐borne and ground‐based instruments

Abstract

The atmospheric response in the aurora (ARIA) rocket was launched at 1406 UT on March 3, 1992, from Poker Flat, Alaska, into a pulsating diffuse aurora; rocket‐borne instruments included an eight‐channel photometer, a far ultraviolet spectrometer, a 130.4‐nm atomic oxygen resonance lamp, and two particle spectrometers covering the energy range of 1–400 eV and 10 eV to 20 keV. The photometer channels were isolated using narrow‐band interference filters and included measurements of the strong permitted auroral emissions N2 (337.1 nm), N2+ (391.4 nm), and O I (844.6 nm). A ground‐based photometer measured the permitted N2+ (427.8 nm), the forbidden O I (630.0 nm), and the permitted O I (844.6 nm) emissions. The ground‐based instrument was pointed in the magnetic zenith. Also, the rocket payload was pointed in the magnetic zenith from 100 to 200 km on the upleg. The data were analyzed using the Strickland electron transport code, and the rocket and ground‐based results were found to be in good agreement regarding the inferred characteristic energy (E0 ≈ 3 keV) of the precipitating auroral flux and the composition of the neutral atmosphere during the rocket flight. In particular, it was found that the O/N2 density ratio in the neutral atmosphere diminished during the auroral substorm, which started about 2 hours before the ARIA rocket flight. The data showed that there was about a 10‐min delay between the onset of the substorm and the decrease of the O/N2 density ratio. At the time of the ARIA flight this ratio had nearly returned to its presubstorm value. However, the data also showed that the O/N2 density ratio did not recover to its presubstorm value until nearly 30 min after the particle and joule heating had subsided. Both the photometer and oxygen resonance lamp data showed the presence of structure in the atomic oxygen densities in the region above 130 km. The observed auroral brightness ratio B337.1/B391.4 equaled 0.29 and was in agreement with other recent measurements. This ratio was also consistent with the greater than expected flux of secondary electrons measured by the onboard particle spectrometer between 40 and 10 eV.