Variability of eddy diffusivity in the stratosphere deduced from vertical distributions of N₂O and CFC-12

Abstract

The vertical distributions of eddy diffusivity in the stratosphere, calculated from the vertical mixing ratio profiles of N₂O and CFC-12, are discussed. A photochemical equilibrium model has been formulated to evaluate the eddy diffusivity in the stratospheric altitude region of about 17-38 km. An attempt has been made to study the temporal variability from the measured vertical profiles during the balloon flights in the years of 1987, 1990 and 1994 conducted from a tropical site, Hyderabad (17.5 °N, 78.6 °E). The present calculated eddy diffusion coefficients are higher than those estimated earlier using a similar procedure (Massie and Hunten, 1981) for average midlatitudinal conditions. Richardson numbers are also calculated from the wind and temperature profiles and the persistence of turbulent layers are studied. A probable range of eddy diffusion coefficients is proposed for the equatorial region. The lower limit agrees well with the values of NAS (1979) and the higher limit, almost constant over the complete altitude region (≈7 × 10⁴ cm²s^-1), roughly follows the in situ measurements using puff release experiments over the same location.