自然天气季节的概念,最早由牟尔汤诺夫斯基提出。这是指在一年中天气过程可分成几个阶段。在同一个自然季节中,各个大气活动中心的作用保持不变,因而有一定的作为季节特点的天气过程。

From an analysis of the vertical profile of the middle-high latitudes (45?-65癗), the mean westerly geostrophic winds and the tonal index at 500-mb level, it is found that, the annual march of the general circulation at 500-mb over East-Asia may be divided into several distinct stages. Close relation is also found among the general cir- culation, secular fiv e-day mean temperature and precipitation of the North-West China. Based on the above mentioned factors, seven natural synoptic seasons are recognized, i.e., early Winter, middle }}Vinter, late Winter, Spring, early Summer, deep Summer and Autumn. With respect to the length and weather conditions of the seasons are quite different from each other. Demarcation of the natural synoptic seasons is helpful to the long range weather prediction of the region concerned.