Why does it rain so much in Tomb-Sweeping Day?

The phenomenon of "like mushrooms after rain" often appears in Tomb-Sweeping Day, mainly because of meteorological conditions and climate characteristics. It's mid-spring in Tomb-Sweeping Day, and the temperature is getting warmer. In the process of global warming, the cold air force in the north is gradually weakening, but it has not been completely withdrawn, while the warm and humid air flow in the south is gradually active and pushing northward. When these two air streams meet, the intersection of cold and warm air can easily lead to precipitation. In addition, due to the adjustment of atmospheric circulation and the influence of topography, there are frequent cyclone activities and many low-pressure systems in spring, which is conducive to the formation of rainy weather.

Specifically, the following factors led to the rainy phenomenon during the Qingming period:

1. Convection of cold and warm air: At this time, the cold air in the north and the warm and humid air in the south meet in the Yangtze River basin, and the cold and warm air flows interact to form a front, thus generating precipitation.

2. Terrain influence: Terrain uplift makes the warm and humid air flow cool and condense in the rising process, forming precipitation.

3. Climate characteristics in spring: the temperature rises rapidly in spring, the surface evaporation increases, and the water vapor content in the air increases, which is easy to form precipitation conditions.

4. Atmospheric water vapor content: Before and after Tomb-Sweeping Day, the atmospheric water vapor content was high, which was triggered by favorable weather system and was easy to form precipitation.

Therefore, the "rainy season" described in ancient poems vividly reflects the unique climate characteristics of this period.