What are high clouds mostly composed of?

High clouds, typically classified as cirrus, cirrostratus, and cirrocumulus, are primarily composed of ice crystals. These clouds form at altitudes of about 20,000 feet and higher, where temperatures are significantly colder. The low temperatures at these heights lead to the formation of ice crystals instead of water droplets.

Due to the colder atmospheric conditions, the water vapor present in the atmosphere condenses and freezes, resulting in the characteristic thin and wispy appearance of high clouds. This composition contributes to their unique optical phenomena, such as halos around the sun or moon, which occur when light refracts through the ice crystals.

In contrast, water droplets are more prevalent in lower clouds, where temperatures are warmer. Pollutants and rain are not characteristics of high cloud composition; pollutants can occur in any cloud type depending on the environment, but they do not define high clouds. Rain typically forms from lower and thicker clouds where sufficient moisture and temperature allow for the coalescence of larger water droplets.