Atomic nitrogen measurements in the upper atmosphere

The open source neutral mass spectrometer (OSS) on the Atmosphere Explorer‐C satellite (AE‐C) measures the neutral constituents of the upper atmosphere. It has been found that atomic nitrogen densities can be determined at altitudes above 380 km. Most of the nitrogen atoms combine with oxygen adsorbed on the walls of the ion source to form NO. The measured net peaks at 14 amu and 30 amu show the scale height expected for atomic nitrogen; both peaks have a pronounced diurnal variation. We computed absolute number densities at 400 km for a time period between February and April 1974 when measurements were taken in the northern hemisphere. Minimum and maximum densities of atomic nitrogen occur between 4 and 6 hr LST in the morning and around 16 hr LST in the afternoon, respectively. At 400 km the minimum particle density is 1.0 × 10 5 cm −3 and the maximum density 1.5 × 10 6 cm −3 . In contrast to the response of N 2 to geomagnetic activity, atomic N shows no appreciable effect.