Positive ions in the mesosphere.

Positive ions have been measured using the parachute borne blunt probe, a subsonic system launched on meteorological rockets, which measures polar electrical conductivities in the 30 to 80 km altitude range. A central feature of the daytime positive conductivity profiles is a sharp break occurring between 60 and 70 km which indicates the transition from galactic cosmic ray to solar ultraviolet ionization, and, hence provides information about the nitric oxide density. In the 50-60 km region the positive ion conductivity is relatively constant with altitude and correlates well with atmospheric temperature down to 35 km. Using temperature and pressure profiles and a reduced mobility, the conductivity profiles may be converted to density profiles. The average mid-latitude daytime profile at intermediate solar zenith angles showed a minimum at 63.5 km.