Clouds

Clouds are visible masses of liquid water droplets or ice crystals suspended in Earth's atmosphere. They form when air parcels rise and cool to the point of saturation, allowing water vapor to condense around particles known as cloud condensation nuclei. Their appearance, altitude, and structure depend on humidity, air stability, and temperature.

Cloud formation begins when air rises and cools, reaching saturation so water vapor condenses around cloud condensation nuclei. In upper or colder regions, water droplets freeze into ice crystals, creating ice clouds or mixed-phase clouds. Microphysical properties such as droplet size and ice fraction influence visibility, brightness, and precipitation potential.

High clouds above roughly 6,000 meters include cirrus, cirrostratus, cirrocumulus. Middle clouds at roughly 2,000 to 6,000 meters include altostratus, altocumulus, and sometimes nimbostratus. Low clouds below about 2,000 meters include stratus, stratocumulus, and cumulus. Cumulonimbus denotes tall, vertically developed clouds associated with strong storms.

Clouds influence climate by reflecting sunlight and trapping infrared radiation, contributing to the planet's energy balance. They are central to the hydrological cycle, supply precipitation, and affect regional weather. Observation relies on meteorological charts, satellite imagery, and radar; cloud cover is a key variable in forecasts and climate models.