In meteorology, precipitation is called water, which falls to the surface of the earth from the atmosphere in liquid or solid forms under the action of gravity. Therefore, phenomena such as rain, snow, hail are rainfall. Consider the question of how rain, snow, hail, and also dew and hoarfrost are formed.
What are clouds and clouds?
Before discussing the issue of how rain and other types of precipitation are formed, we will consider such natural objects as clouds and clouds from the point of view of physics, since they play an important role in the process of precipitation.
Clouds and clouds are an accumulation of small droplets or crystals of water that are suspended in the atmosphere. Whether a given cloud consists of crystals or small droplets of water depends on the height of the cloud above the earth's surface and temperature. Clouds form as a result of the fact that warm and moist masses at the surface of the water in the seas and oceans rise, cool and condense into small droplets. These drops are so small that they are not visible to the naked eye. Their combination forms clouds and clouds. If these drops, for one reason or another, begin to increase in size, then they will fall to the ground.
Rain
To understand how rain forms, you should pay attention to the size of the water droplets suspended in the atmosphere that make up the cloud. When these drops begin to collide and connect with each other, then at a certain critical size, the force of gravity will cause them to fall down to the ground. Moreover, they acquire a speed of 4 to 8 m / s.
The raindrop has a size of the order of 1 mm (0.7 mm to 5 mm). To achieve this size, droplets of the cloud must increase their mass millions of times. In this regard, the thickness of the cloud should be greater than a certain size. Some clouds can reach a thickness of 12 km, while they can lead to the formation of powerful and prolonged downpours, and in some cases even hail.
The large thickness of the clouds and clouds allows droplets to rise upward in their thickness, connecting with other droplets. As a result of this process, large drops form, which fall in the form of rain. Another mechanism that explains how rain forms is as follows: rising in the thickness of the cloud, a small droplet cools and crystallizes. These crystals fall to the ground, when they fall, they heat up and turn into water.
Virg phenomenon
Virga is rain that occurs in the atmosphere but does not reach the surface of the earth. This natural phenomenon can be explained if we consider the issue from the point of view of physics. How does this kind of rain form? The fact is that between the large cloud, capable of precipitation, and the surface of the earth there may be layers of air masses that will be very hot and dry. In this case, drops of water falling from the thickness of the clouds when they fall into these hot and dry air masses will simply evaporate again and never reach the surface of the earth.
Snow formation
We continue to examine the question of how rain, dew and snow form . Now let us dwell on the formation of solid precipitation - snow.
Snow is a solid form of water that falls on the surface of the earth in the form of snowflakes. Snowflakes form when small droplets of water in clouds are cooled to temperatures below 0 ° C and crystallize. In order for snow to form, not enough low temperatures, there must still be some level of humidity in the atmosphere. There are places on earth that are quite cold, but because of the dry air, there is practically no snow in them.
Hail formation
Exploring the question of how dew, hoarfrost, rain and snow are formed, one cannot but mention hail. Unlike snow, which is sufficient for the formation of low low temperatures, hail is formed when the temperature is below -15 ° C. As the temperature in the atmosphere decreases with increasing altitude, hail forms in the upper part of thick clouds, where temperatures drop to -50 ° C. Such clouds are called cumulonimbus. In their lower part, water is in the form of small liquid droplets, and in the upper part - in the form of ice crystals. These crystals gradually grow due to droplets of water rising from the bottom of the cloud due to ascending air currents. When the crystalline reaches a critical size, it falls to the ground. Note that not all ice crystals reach the earth's surface because they melt during the fall.
Dew and hoarfrost
We conclude our discussion of how rain, snow, dew and hoarfrost are formed by a physical explanation of the last two phenomena, that is, the formation of dew and hoarfrost.
Both of these phenomena are associated with diurnal temperature fluctuations in the atmosphere. To understand them, one should know that the solubility of water in a gaseous form in the atmosphere depends on temperature. The higher the temperature, the more water in the form of steam can dissolve in it. In the afternoon, the sun warms the air and leads to the evaporation of water and an increase in humidity in the atmosphere. At night, the air cools, the solubility of water vapor in it decreases, excess water condenses in the form of small droplets that fall in the form of dew.
Hoarfrost is formed in a similar way, only in this case either the air temperature drops below zero, which leads to freezing of water droplets in the atmosphere, or the earth's surface is quite cold, and the dew that has fallen on it crystallizes.