Clouds and Water Vapor
Résumé
Water, in any of its states: vapor, liquid or ice, is a key component of our climate system. It is the coexistence of these three phases of water on Earth that makes it such a special planet. Water vapor is the most important natural greenhouse gas; it contributes up to 60% of the natural greenhouse effect! Thus, water vapor is the second heat source after the sun for heating Earth's surface. Passive sensors are by far the majority in the panorama, and the estimation of water vapor from their measurements is based on the use of the absorption band and the emission band. A cloud consists of droplets of liquid water and/or ice crystals suspended in saturated air aggregated around particles of various origins that promote condensation and are called “cloud condenstation nuclei”.