Model study of atmospheric transport using carbon 14 and strontium 90 as inert tracers

Model calculations for cabon 14 begin at October 1963, 9 months after the conclusion of the nuclear bomb tests; the initial conditions for the calculations are derived by three methods. The model results are compared to the stratospheric measurements. The measured carbon 14 vertical profiles at 31°N are qualitatively different from all of the models; the measured vertical profiles show a maximum mixing ratio in the altitude range of 20 to 25 km from October 1963 through July 1966. Strontium 90 data indicate that aerosol settling is important up to at least 35 km Strontium 90 data indicate that aerosol settling is important up to at least 35 km altitude. Relative to the measurements, about three quarters of the models transport carbon 14 from the lower stratosphere to the troposphere too rapidly, and all models with all three sets of initial conditions appear to sweep carbon 14 out of the midstratosphere (above 28 km) much more slowly than was observed from 1963 to 1970. -from Authors