Why does it rain at night in Lhasa, Tibet?

Because Tibet is full of plateau slopes and towns are built in river valleys near water sources, Lhasa is located in Lhasa River Valley. On the Qinghai-Tibet Plateau, the 24-hour temperature change is obviously influenced by the radiant heat of sunlight. At the same time, due to the great difference in altitude between hillside and valley, the temperature difference at different altitudes at the same time is also very obvious. The higher the altitude, the lower the temperature. Every morning, the plateau is strongly radiated by the local scorching sun, and the earth absorbs the radiant heat of the sun, and the temperature generally rises. After noon, the temperature of the earth rose to the highest point. Since the afternoon, the radiant heat absorbed by the earth from the sun has gradually decreased, and the heat dissipation rate of the earth has gradually accelerated. At this time, the hillside highlands with high altitude first began to cool down, and the atmospheric temperature at the same altitude as the hillside highlands also decreased. As the air cools, the density increases, and the weight of the air becomes heavier and gradually decreases. The air at high altitude cooled down and landed over the valley area at low altitude, while the warm and humid air in the valley area was low in density and light in weight, and began to rise under the extrusion of the cold air falling on the high slope. When the warm and humid air rises to a certain height, the water in the air begins to condense into countless tiny water droplets suspended in the air, which is the cloud. The cold air on the high slope is declining, and the warm and humid air in the valley is rising; Warm and humid air keeps rising and condenses into small water droplets, so the clouds accumulate thicker and thicker; More and more small water droplets condense and converge with each other, and the water droplets are getting bigger and bigger. Finally, the rising airflow could not hold more and more water droplets, which could no longer be suspended in the air and fell, so it began to rain. It takes a long time from the dry cold air on the high slope to the warm and humid air in the valley, and then the warm and humid air condenses into clouds, and the clouds accumulate into rain. It usually starts in the afternoon and lasts until the evening, when it rains, it is already evening. Rainy nights often drop all the water in the sky in the form of raindrops. Until the next morning, Wan Li was cloudless and sunny. This sunny and rainy weather is determined by the topography of high-slope canyons with an altitude drop of several thousand meters.