Why won't it rain?

Rain comes from clouds in the sky. Clouds in the air are actually the condensation of water, which comes from the evaporation of water vapor on the ground. When the water droplets in the cloud reach a certain level, that is, they cannot be supported by the rising airflow, the water droplets (possibly ice droplets and snowflakes) will fall to the ground, that is, the rain (hail and snow) we see.

The evaporation of water vapor will happen at any time, but it won't rain at any time. In the air, when the temperature is high, the amount of water vapor that can be accommodated is large, and when the temperature is low, the amount of water vapor that can be accommodated in the air is small. When air moves from high temperature to low temperature, water vapor will change from unsaturated to supersaturated and condense into water droplets. When the weight of water drops exceeds the buoyancy of air, it will rain.

As rivers, lakes and oceans are exposed to sunlight, water becomes steam. When the water vapor rises, it becomes small water droplets or ice crystals, and the airflow below constantly transports the water vapor into the clouds. Small water droplets and small ice crystals in the cloud collide with each other in motion, and the volume will increase. The water droplets in the lower layer of the cloud gradually get bigger. After the ice crystals in the upper layer of the cloud increase in volume, they will fall between the water droplets in the lower layer of the cloud, and the water droplets will become larger and larger. When these water droplets are too big for the updraft to drag, it rains.

When water is irradiated by sunlight, it becomes steam and evaporates into the air. Water vapor condenses into small water droplets when it meets cold air at high altitude. These water droplets are very small, with a diameter of only 0. 0 1~0。 02 mm, the maximum is only 0. 2 mm They are small and light, and are held up in the air by the updraft in the air.

It is these small water droplets that gather in the air to form clouds. These small water droplets will become raindrops and fall to the ground, and the volume will increase by about 1 10,000 times.

How did these small water droplets increase their volume to more than 654.38+00,000 times? It mainly relies on two means, one is condensation and sublimation. The second is to rely on the collision and increase of cloud droplets. In the initial stage of raindrop formation, cloud droplets mainly condense and condense themselves by constantly absorbing water vapor around the cloud.

If the water vapor in the cloud can be continuously supplied and replenished,

If the surface of cloud drops is always in a state of supersaturation, then this condensation process will continue, making the cloud drops grow and become raindrops. However, sometimes the water vapor content in the cloud is limited, and in the same cloud, the water vapor is often in short supply, so it is impossible to make every cloud droplet grow into a larger raindrop, and some smaller cloud droplets have to be merged into a larger cloud droplet.

If there are water droplets and ice crystals in the cloud, the process of condensation and sublimation will be greatly accelerated. When the cloud drops increase to a certain extent, due to the increasing volume and weight of large cloud drops, they can not only catch up with the slower small cloud drops, but also "swallow" more small cloud drops, making themselves stronger.

When the big cloud drops get bigger and bigger until the air can no longer hold them, they fall straight from the clouds to the ground and become our common rain.