South China is easily affected by the southeast monsoon in spring and summer, which brings a lot of warm and humid airflow from the sea. However, in order to turn the water vapor in these steam flows into precipitation, it is necessary to have suitable conditions: first, topography, and second, atmospheric convection front. This knowledge should be mentioned in high school geography. As for why the south is dry, it is because the latitude of most parts of southern China is just in the subtropical high zone. After the end of the monsoon, from late July to mid-late June 10, the southern region is controlled by subtropical high, with high temperature and little rain. This season, the temperature is high, the evaporation is large, and the rainfall is small, which is easy to form summer drought or autumn drought. In fact, many latitudes in the world have arid tropical desert climate or savanna climate. However, the south of China lies on the mainland coast. During July 7- 10/0, typhoons often pass by, temporarily breaking the climate mode controlled by subtropical high and bringing a lot of rain. When there are few typhoons, summer drought usually occurs in southern China, even in summer and autumn, such as this year (20 1 1).

After the end of June 65438+ 10, the subtropical high usually withdrew from South China, and the dry and cold air in the north began to move southward gradually. In this process, the intersection of north and south airflow will form some small-scale rainfall, which is the common cold climate in autumn and winter in the south. Once the dry cold air in the north completely dominates, the weather in the south will turn into dry, cold and sunny weather, usually at the end of June165438+February 65438+February, when frost is easy to form.

From the above analysis, it can be seen that dry weather is easy to form in summer, autumn and even winter in southern China, but such weather is easily changed by the changes of north-south airflow and typhoon intensity in different years, but the drought in the second half of the year is usually a high probability event. If the warm and humid steam flow in the south is not enough to shake and control the cold and high-pressure air mass in the south in spring (+10 at the end of June, 65438), a spring drought will also occur.