Transport of air in the stratosphere as revealed by radioactive tracers

Abstract

The available measurements on cosmogenic ⁷Be and artificial tracers ¹⁰⁹Cd and ²³⁸Pu in the atmosphere are discussed in terms of plausible circulation patterns in the stratosphere and across the stratopause. The ⁷Be data in the northern hemisphere between 24 and 37 km, when integrated with the aircraft data from lower altitudes, suggest an equatorward transport of polar air above 25 km during the winter of 1965. Such a motion does not seem to be operative below 24 km. There are cyclic variations in the concentration of ¹⁰⁹Cd and ²³⁸Pu in both hemispheres which are out of phase by about six months; in early spring through summer, the concentrations are repeatedly higher than in the fall and winter during 1962-1965 at 34°S and 31°N. These data indicate that the transport across the stratopause is strongly seasonal and probably takes place during an extended spring period. A detailed analysis of tracers injected in the mesosphere further suggests that the dispersion history of the debris injected in the mesosphere strongly depends on the time of injection.