Study on Horizontal Relative Diffusion in the Troposphere and Lower Stratosphere

The behaviour of relative diffusion theory and Gifford’s random-force theory for long-range atmospheric diffusion is examined. When a puff scale is smaller than the Lagrangian length scale, 2KTL, an accelerative relative diffusion region exists, i.e., σy∝t3/2. While the puff diffusion enters a two-dimensional turbulence region, in which the diffusion scale is larger than 500 km, or time scale is larger than 1 day, divergence and convergence are main cause of horizontal diffusion. Between the two above-mentioned regimes, diffusion deviation is given byσy=2KTL. The large-scale horizontal relative diffusion parameters were obtained by analyzing the data of radioactive cloud width collected in air nuclear tests.