Seasonal climate season

Dividing seasons according to the distribution of climatic factors. The climate season in China was first studied by Zhang (1934). In his article The Distribution of Four Seasons in China, he proposed that the average temperature in five days in winter is below 10C, above 22C in summer, and between 10 ~ 22c in spring and autumn, and drew the length of four seasons in different places. Because the temperature above 10C is suitable for the growth of most crops, and the time above 10C in a year has great influence on agricultural production, it is of great practical significance to divide the seasons in this way.

In addition to temperate seasons, other climatic zones often use other climatic factors to divide climatic seasons because of their special climate. In tropical and sub-tropical areas, the annual change of temperature is small, and the seasons are often divided by the change of precipitation or wind direction, so there are dry seasons and rainy seasons; Northeast trade wind season and southwest trade wind season, etc. This method of dividing seasons is particularly common in the South Asian subcontinent. In most parts of North Africa, a year is divided into three seasons: cool season, hot season and rainy season. Near the polar regions, it is divided into two seasons, namely, summer with eternal days and winter with long nights.

On the plateau of Qinghai-Tibet, the winter is dry and windy, and the summer is rainy for more than half a year, so the whole year can be roughly divided into two seasons: the wind season (dry season) and the rainy season. For other areas with different underlying surfaces, such as oceans and inland areas, forests and grasslands, due to different climates, different criteria for seasonal division can be adopted to meet the needs of local production and life.

Natural weather season: The above-mentioned seasonal division methods do not consider weather factors, so most of them are not suitable for studying the interannual variation of seasons. In the 1920s, Soviet climatologist Mulitanovsky first put forward the concept of natural weather season. He divided the seasons according to the characteristics of the weather process that formed the climate, and divided the European part of the Soviet Union into five seasons: spring, summer, autumn, previous winter and winter. Later, C.T. Pagava divided summer into early summer and midsummer. In 1950s, Yang Primary School in China studied the natural weather season in East Asia according to the circulation pattern of 500 hectopascals. The division of natural weather seasons is one of the research contents of weather climatology, which is of great significance to long-term weather forecast. However, due to the complexity of the weather process, there is still a lack of objective or unified standards for the division of natural weather seasons. Therefore, the start and end dates of the season are not easy to determine. At the same time, for a natural weather season, the weather performance is different because of different locations and different weather systems. Therefore, the concept of natural weather season is still immature and needs further study.