Through the Clouds
The summit of Mount Alberta in Jasper National Park in Alberta, Canada, peaks up through a thick layer of cloud cover.
Photograph by Dean Conger / National Geographic
Clouds form throughout all the levels of the atmosphere and affect both weather and climate. The type and amount of clouds that commonly form over a region impact the precipitation conditions. Cloud cover may also influence temperatures at the surface of the planet.
Water evaporates from the ground and condenses in the atmosphere, resulting in a wide variety of cloud shapes: from large, puffy clouds to wispy formations. When there are few clouds in a region, it generally signals the presence of a high-pressure system, which means that residents can expect fair weather and no precipitation. Certain clouds, such as low-level, short, cumulus clouds, indicate that fair weather is moving into the area. Residents can expect sunny skies and little precipitation. When high-level cirrus or low-level stratus clouds increase in a region, the region can expect to see precipitation from an incoming low-pressure system. Cirrus clouds are thin, wispy clouds that usually occur in the upper levels of the atmosphere ahead of a storm. Stratus clouds are thin-layered, gray clouds that can result in light precipitation.
Most clouds take on these three basic shapes—cumulus, cirrus, and stratus—and are further classified as nimbo-form if they bring rain. For example, thick, gray, stratus clouds that bring heavy precipitation are called nimbostratus.
However, clouds do more than bring rain or fair weather. Clouds also act as an “atmospheric blanket” that helps to regulate the temperature at Earth’s surface. During the day, clouds reflect a portion of the solar energy that reaches Earth back into space. This prevents the planet from becoming too warm. Clouds can also act like a blanket, trapping heat on Earth by absorbing the heat released by the surface of the planet. They radiate this heat back toward Earth, warming the lower regions of the atmosphere. Whether clouds heat or cool the surface of Earth depends on the height and type of cloud present in the sky. High-level, feathery clouds help heat the planet during the day, allowing sunlight to penetrate the surface and prevent heat from escaping. Meanwhile, lower level clouds often reflect heat from the sun back into space and keep the surface temperatures cool.
Cloud cover can also limit the cooling that occurs in a region at night. Typically, the solar heat absorbed by the ground during the day is released at night as Earth cools. The warm air near the ground rises in a process known as radiative cooling. However, if thick cloud cover is present over a region where such radiative cooling is happening, some of the heat is trapped and reflected back to Earth by the clouds. This keeps the surface warmer than it would be during a night without cloud cover.
thin, high-altitude cloud.
visible mass of tiny water droplets or ice crystals in Earth's atmosphere.
amount of sky covered with clouds.
type of large cloud with a flat bottom and fluffy tops.
weather pattern characterized by high air pressure, usually as a result of cooling. High-pressure systems are usually associated with clear weather.
weather pattern characterized by low air pressure, usually as a result of warming. Low-pressure systems are often associated with storms.
all forms in which water falls to Earth from the atmosphere.
precipitation made of ice crystals.
mid-level clouds found up to an elevation of about 2000 meters above the Earth.
degree of hotness or coldness measured by a thermometer with a numerical scale.