On the Characteristics of the Scales of the Atmospheric Motions

[摘要] It is shown in this paper that the development of most of the atmospheric weather systems, large-scale or small-scale, consists of three stages, namely the adjustment stage (called geostrophic adjustment for large-scale motions), the developing stage and the quasisteady stage. There are three time scales corresponding to these three stages of development, the time scale for the adjustment stage being shortest, that for the developing stage being much longer and that for quasi-steady stage being longest. The physical processes in the development of these three stages are related to the evolution of the potential vorticity field.It is further shown in this paper that similar to the scale effect in large-scale motion with a critical scale L0=c/ƒ, there is also a critical scale L0'=c/Ω for meso-scale motion, where c is the speed of gravity wave;ƒ, the Coriolis parameter and Ω, the characteristic value of absolute vorticity of the wind. Under certain assumptions, a critical scale L0"=[u2/g/ρ∂ρ/∂z]1/2 can also found for motions of cumulus scale, where u and ρ are the characteristic velocity and density of the atmosphere respectively. The roles of L0' and L0" in meso-scale and cumulus-scale motions are similar to that of L0 for large-scale motions.

[学科分类] 大气科学