Seek the specific reasons for the rainy and changeable weather in Ya 'an.

Answer 1: The leaking sky in rainy city is the result of the interaction of several air currents.

"The water leakage in Yucheng is actually caused by the special geographical environment in which Ya 'an is located. Guikang Peng, senior engineer of Ya 'an Meteorological Bureau, told us. Since the early 1990s, experts from Guikang Peng and lasg have made a systematic study on "the city with leaking rain in the sky".

He said that to the west of Ya 'an is the Qinghai-Tibet Plateau, known as the roof of the world, and to the east is the Sichuan Basin, thousands of miles away. Ya 'an is located between these two completely different landforms, and is often influenced by the interaction between the warm and humid airflow flowing downward from the plateau and the basin. In addition, a large number of warm and humid air currents are carried by the westerly winds from the southern branch of the Indian Ocean and are often forced to move eastward around the plateau into Ya 'an. The interaction of these air currents leads to more rainy days, longer rainfall time and heavy rainfall in Ya 'an.

He pointed to a topographic map of China and showed it to us. It can be clearly seen from the map that Ya 'an lies between the plateau and the basin. Even a layman can imagine that once there is any trouble in the air flow over the plateau and basin, Ya 'an will encounter rain.

Answer 2: The leaking weather in rainy city is caused by Ya 'an trumpet-shaped terrain.

"There is another important reason for the leakage of rain in Yucheng, which is created by the unique geographical form of Ya 'an. Liu, director of the Ya 'an Meteorological Observatory, added that he has been engaged in forecasting for many years, and it is not difficult to find that Yucheng seems to be a "little daughter-in-law" who suffers indignities, and her personal freedom is completely controlled by her husband and in-laws: the tall and majestic Erlang Mountain in the west, the steep mountain in the northwest, the Big Xiangshan Mountain in the south and only one exit in the east.

This terrain is trumpet-shaped, and the warm and humid airflow from the east can only enter but not exit. At night, the cold air in the surrounding mountains sinks. Once the cold air meets the warm air, the wronged "little daughter-in-law" in Yucheng can only Lacrimosa-it rains intermittently, which is also the reason for the rainy night in Ya 'an.

Answer 3: Rain City Sky Leakage is the water vapor transported by the southerly air flow in the Pacific Ocean.

In addition, Liu also pointed out that the leak in Yucheng needs a lot of warm and humid water vapor. From the analysis of atmospheric circulation situation, the atmospheric circulation that transports water vapor to Yucheng includes Pacific subtropical high and southerly airflow. With their help, the sky in "Rain City" keeps leaking rain.

Answer 4: The most fundamental reason for leaking the sky in rainy cities is topography.

Judging from the explanations of two experts, "the most fundamental reason for the rainy city leaking the sky is the topographic factor, because there is not much rainfall in other areas adjacent to Ya' an, especially the two counties of Luding and Hanyuan on the side of Erlang Mountain and Daxiangling, which are very different from Ya' an." Liu He told us.

In order to confirm what the experts said, after the interview, we crossed Erlang Mountain along the Sichuan-Tibet Highway. As a result, we were surprised to find that the climate, landform, vegetation and soil on the east and west slopes are very different just across a mountain. At the foot of Dongpo Mountain, the vegetation on both sides of the highway is lush, and the virgin forest is lush and endless, but the weather is really pleasing, either raining or foggy. As soon as the car turned over the mountain pass and began to go downhill, it was another world: boundless blue sky, bright sunshine, flawless clouds and transparent and fresh air. Looking ahead, you can see icebergs and snow peaks towering into the sky. Looking down at the land at the foot, I saw the rugged yellow land desolate and bleak. The climate here is dry, the hot air is fierce, and the stream is cut off-who would have thought that it is only separated by a mountain, Dongpo and West.

Back in Ya 'an, we will invite meteorologists to analyze this phenomenon. According to Liu's analysis, this phenomenon is related to the complex and peculiar terrain conditions: Erlang Mountain is in an orderly north-south direction, making its eastern slope on the windward side, where a large number of warm and humid air currents condense into raindrops due to uplift, so there is more rain on the eastern slope; The west slope is blocked by a tall mountain, and the warm and humid airflow is almost lost when crossing. After crossing the mountain, the temperature will be too high, resulting in the evaporation of the remaining water vapor. Coupled with the terrain barrier around the western slope, the temperature is high and evaporation is strong, so it is difficult to form clouds into rain, so the climate around the western slope is dry and rainy. It seems that the rainy city is really caused by the unique geographical environment created by nature. But the geographical environment like Ya 'an is unique in the world, so the rainy city in the world can only belong to Ya 'an.