Mesoscale diffusion derived from tetroon flights

A summary is presented of continuous-point-source (CPS) and instantaneous-point-source (IPS) diffusion within the planetary boundary layer as obtained from tetroon flights at Los Angeles, Atlantic City, New York, and Idaho Falls. For downwind distances from 5 to 50 km, the IPS and CPS diffusion is proportional, respectively, to the 0.8 and 0.9 power of distance for the combined data. Over a day, CPS diffusion in the lateral direction is also proportional to release interval (in hours) to the 0.3 power. Based on the classical solution for Fickian diffusion, the coefficient of (horizontal) eddy diffusivity varies from 106 to 107 cm2 s-l. With the additional assumption that tetroon diffusion is a result of eddies within the inertial subrange, the dissipation averages 1.0 cm2 s-3. The variation with time of the square of the separation distance between simultaneously released tetroon pairs is in good accord with similar data, at larger and smaller scales, obtained by other workers. There is Some evidence that this separation rate is largest from 5 to 10 minutes after release for pairs initially separated by the order of 100 meters. (author)