Lowermost region of a planetary atmosphere where Transfer of heat energy by moving material. Temperatures increases with depth in planetary objects. Deep hot less-dense material physically rises and cools, releasing heat and becoming denser. The now cooler denser material sinks back into deeper regions, where it will be reheated and rise again. Convection is an important mechanism Click on Term to Read More keeps the gas mixed and maintains a steady decrease of temperature with height. Most clouds are in the troposphere.