Downloads & Free Reading Options - Results

This paper reviews radioactive tracer data to determine effective stratosphere-to-troposphere transfer rates for a one-dimensional parameterization. The basic data used are the time-dependent global stratospheric burdens of Zr95 following six Chinese thermonuclear explosions 1967-1976, and also the falloff in burdens of Sr90 and excess C14 following the very large Soviet and U.S. test series of 1961-1962. Results of the Chinese explosions demonstrate that transfer of material from stratosphere to troposphere is fast in winter but slow in the summer of initial injection. It is best modeled by a seasonally varying eddy diffusivity profile, showing 'fast' transport (e.g., Dickinson-Chang, Danielsen) for a winter injection, and fast transport delayed to the next winter for a summer injection. Cloud rise height for the 1961-1962 tests is not well known, and so two models for the yield-altitude curve are used: a 'high' (Foley-Ruderman) and a 'low' (Seitz) model. The overall time variation in stratospheric burden of Sr90 and in stratospheric and tropospheric burdens of C14 can be simulated best by relatively fast falloff, i.e., by using a low injection height (Seitz) and fast transport (e.g., Dickinson-Chang). The difference in falloff rate of stratospheric burdens of Sr90 and of C14 is due principally to the recycling of C14 (as CO2) from the troposphere, with minor corrections due to sedimentation of the aerosols carrying Sr90 and the difference in effective injection height of these two tracers.