Clouds – what are they and how do they affect weather?
Clouds consist of water vapor condensed into droplets or deposited into ice crystals. The droplets or ice crystals float in the lowest layers of the atmosphere and are carried by air currents.
Rain is formed inside clouds: as water vapour condenses, clouds form, and if enough condensation happens and cloud droplets become heavy enough, also rain will fall. Clouds transport heat and protect us from ultraviolet radiation and other harmful radiation coming from space.
Clouds protect the Earth
Clouds limit the heating of the Earth, because they reflect part of the radiation coming to Earth back to space. As an example, cloudless deserts are usually very hot, since very little solar radiation is reflected away, and most of the solar radiation reaches the ground and heats it. If the Earth had no clouds, the tropics would heat much more than they do now, and tropical regions might be rendered uninhabitable.
Clouds also protect the Earth from excessive cooling, especially in high latitudes during winter months, as clouds prevent heat from escaping into space. If there were no clouds during winter, high latitude areas on Earth might be partly uninhabitable. When skies are clear in wintertime, temperatures drop quickly, because clouds don’t stop the heat from escaping.
Cloud formation
Cloud formation starts when water evaporates from oceans, lakes, rivers, plants and the soil. We are constantly surrounded by invisible water vapour. If rising air currents lift this water vapour, it begins to condense as the temperature of the air decreases with height. The water vapour becomes visible and clouds are formed. When this happens just above the ground, the appearing cloud is called fog.
If enough moisture is available, cloud droplets grow. When the droplets grow heavy enough, they fall down as rain. As height increases and temperatures inside the cloud fall below freezing, ice crystals start to dominate over water droplets inside the cloud.
Article last updated 2/25/2021, 8:09:00 AM
