| Abstract: | 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∝ t
3/2. 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 by σy = √2KT. The large-scale horizontal relative diffusion parameters were obtained by analyzing the data of radioactive cloud
width collected in air nuclear tests.
This work is sponsored by the National Natural Science Foundation of China under Grant No. 49505064.
The author would like to thank Prof. Chen Jiayi Department of Geophysics of Peking University and Dr. Cai Xiaoming School
of Geography and Environmental Sciences of Birmingham University for their helpful discussions. |
