How is the weather created?

The air contains water vapor which can absorb energy well, and the water vapor in the air can be continuously replenished. In the continuous circulation, water evaporates from land and sea and gathers into clouds. Then rain, snow or other forms of precipitation are produced, and the whole process is self-circulating.

Water molecules in the atmosphere constantly change back and forth between gas, liquid and solid. Rain falling from the clouds means that more water molecules leave the gas state and form small water droplets (condensation), while water molecules enter the gas state (evaporation) from the state of small water droplets.

These two processes, condensation and evaporation, are always going on in the air around us, but the speed will be different because of different temperatures. For example, on a clear, cloudless and sunny day, heat will accelerate evaporation and prevent water droplets in the air from surviving for too long. Therefore, there are more water molecules returning to water vapor than those existing in the form of small water droplets. When the air cools, the evaporation rate will decrease until the evaporated water molecules are less than the condensed water molecules: at this time, we say that the air is saturated and the water vapor usually condenses into small water droplets, forming clouds, fog and dense fog.