How rain forms

 How clouds are formed and bring us rain?

Rain forms in clouds gradually in several stages as follows:

  • Clouds are formed from water vapor that reaches them as a result of water evaporation from the surface of the earth or by plants that release water and oxygen during the process of photosynthesis, where the water vapor rises to the upper atmosphere and condenses and turns from its gaseous state to a liquid or solid state such as ice. 
  • The water droplets gradually increase with the continuation of the condensation process and increase in size and consequently increase their weight. 
  • The condensation process continues until the cloud becomes completely saturated and very heavy, and the load is discarded in the form of rain, and some clouds appear black due to being filled with raindrops that prevent sunlight from Pass-through. 
  • The type and shape of rain precipitation from the cloud depends on the temperature of the surrounding air and below it. 
  • If the temperature of the air surrounding the cloud reaches its freezing point, any temperature is 0 degrees Celsius or less than that, then the water drops in the cloud crystallize into the snow and then fall. 
  • The temperature of the atmospheric layers below the cloud is below zero, and the precipitation will be snow, and if the temperature differs between the cloud and the earth and the layers alternate between hotter and less hot, the type of precipitation will differ in each layer, for example, in the clouds above the tropics, the precipitation begins in the form of drops water continues as it is until colliding with the surface of the earth, but in most parts of the world, the drops of rain will be in the solid-state in the cloud and melt during the fall because of the relatively warm air near the surface of the Earth.

Factors affecting rain formation

The distribution of rain on the Earth's surface is affected by several factors, as follows:

  • Ascending and descending air currents: the air is cooled and ascended to the upper atmosphere by expansion, as the evaporation of water from the surface of the earth transforms it into a low-density vapor and a larger volume, which leads to its high rise, so it condenses in the clouds and produces rain as in tropical forests where it gets a high rate of precipitation It reaches a meter per year, and on the contrary, the downward air currents produce desert areas with large areas on the ground, where the descending air is heated due to pressure and absorbs moisture instead of releasing it.

 It is known that deserts get low rates of rain less than a centimeter per year.

  •  Air temperature: When the temperatures drop, the humidity in the air decreases, which means that water droplets do not condense in proportions suitable for precipitation.
  •  Marine currents: When winds blow over the surface of the ocean, the evaporation of water is active and is directed towards coastal areas, especially if the winds are over warm water areas, and these areas get a higher rate of precipitation than the areas where the winds blow from the coast towards the ocean.
  •  Distance from the coast: coastal areas close to water bodies such as seas, oceans, and lakes get a higher rate of precipitation than areas far from the coast, as the winds lose moisture gradually with an increase in their distance from the coast and may reach dryness in areas far from the coast. 
  • Mountain chains: When winds are intercepted by mountain chains, they force them to rise, and the occurrence of condensation of air and precipitation, and unlike slopes and low-lying areas, the percentage of precipitation decreases.

The shape and size of the formed Raindrops. 

Raindrops are usually formed with a radius not exceeding 1 mm and their shape is like a round ball, and with the collision of the droplets and their merging with each other their size increases, and during their precipitation in the layers of the atmosphere they are exposed to the resistance of the air, which flattens their bottom as they become flat from the bottom and reach a diameter of 2-3 mm and maintain their spherical shape From the top, and its size continues to increase with each collision with other drops, to reach a diameter of 4-5 mm, then the structure of the drop begins to collapse from a certain point to become like an umbrella, and it continues to expand until it splits into smaller drops, and according to scientists, the minimum diameter of raindrops is 0.5 Mm and less is called a mist, and the spray usually falls from low-altitude clouds. 

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