The Determination of Diffusion Coefficients in a Shearing Flow by Chemical Tracer Techniques.

摘要

A practical technique has been developed for obtaining scalar diffusion coefficients and local wind shears from photographic observations of chemical tracer puffs deposited in the atmosphere. Analytic solutions have been obtained which indicate that the puff density is a Gaussian function of space at each time for the practically important case of an atmosphere possessing constant scalar diffusion coefficient with a horizontal wind field having constant vertical shear. It is shown that the sum of the Gaussian half-widths squared projected on the film plane is a cubic polynomial in the time with coefficients that depend on the geometry,the shears and the diffusion coefficient,whence these parameters can be determined experimentally by a least squares fitting procedure. The technique has been tested by application to a recent experiment in the lower thermosphere. The results of this test are presented and compared with results derived earlier by the use of conventional techniques. (Author)