Scale effect of weather system

The spatial scale (horizontal and vertical) and time scale of various weather systems, as well as the characteristic horizontal wind speed, are determined according to actual observations. However, some quantities can not be directly observed until 2 1 century, and can only be calculated according to the atmospheric dynamic equation. In numerical calculation, it is necessary to choose an appropriate spatial lattice distance, and its size is determined by the characteristic scale of the system, which is the scale effect. For example, the characteristic vertical velocity of a weather system can be calculated from the horizontal scale and the characteristic horizontal wind speed according to the continuous equation. The vertical velocity of various weather systems has certain characteristic values, such as 10- 1 cm/s for planetary scale weather systems, 10 cm/s for weather scale weather systems and 102 cm/s for small scale weather systems.

Since the appearance of scale analysis method in the late 1940s, people often simplify the complete equations of motion according to the characteristic scales of various weather systems, and study the laws of atmospheric motion and the motions of various systems. For example, quasi-geostrophic equilibrium approximation and statics can be applied to the study of weather-scale weather systems, while small and medium-scale weather systems do not satisfy geostrophic equilibrium and statics.