On the Geographical Problems of "Clear and Rainy"

During the Qingming period, most parts of China entered the real spring. However, during this period, the weather in the south and the north seems to be two different days. The north is dry and rainy, and the south is wet and rainy.

What Du Mu is talking about here is the rainy weather in Tongling, Anhui Province, which generally refers to the frontal precipitation phenomenon in southern China in spring. In April, the number of days in Jiang Nanyu was around 16, and the rainfall was above 100mm, even more in some areas.

What kind of "rainy" weather often occurs in southern Tomb-Sweeping Day? There are three reasons:

◆ During the Qingming period, the direct point of the sun will be moved from 5 degrees 57 minutes north latitude to 1 1 degrees 32 minutes, and the sunshine in the northern hemisphere will be obviously enhanced. At this time, the western Pacific subtropical high also strengthened its westward extension, and the southwest wind began to strengthen, transporting warm and humid air from the ocean to the south of China.

◆ During Tomb-Sweeping Day, the cold air in the north still has some residual forces. As the cold air goes south, it meets the warm and humid airflow in the Yangtze River basin, resulting in precipitation. When the forces are equal, the formed front area swings back and forth in this area, and the rain area also lingers in the same place.

◆ During the Qingming period, because the warm and humid airflow has not reached the peak, even the strong convective weather system in the rain belt is not as strong as that in summer, so there are relatively few rainstorm centers in the rain area, and the short-term rainfall is not very concentrated, mostly continuous precipitation. Therefore, "it rains one after another during the Qingming Festival", which has become a unique weather phenomenon in April in the south.