Description

Most clouds, including all of the standard clouds, occur in the troposphere, the atmospheric layer closest to the ground. This is where almost all of the water vapor which produces these clouds is found. Clouds visible in the upper atmosphere (above the troposhere) include Polar stratospheric clouds, which form in the stratosphere between about 15 km (50 000 ft) and 30 km (150 000 ft) at high latitudes of both hemispheres during winter, and noctilucent clouds, which form in the mesosphere at altitudes of about 80–85 km (280 000–300 000 ft), at or near the mesopause in summer. Noctilucent clouds are also known as polar mesospheric clouds.