Anthropogenic cloud
The intermediate layers of the troposphere are the regions with less influence of human activity. This region is far enough from the surface for not being affected by the surface emissions. Additionally, commercial and military flights only cross this region during ascending or descending maneuvers. Moreover, in this region there exist two types of clouds with a large horizontal extension: "Nimbostratus" and "Altostratus", which cannot originate from human activity. Consequently, it is assumed that there are no anthropic clouds of these two "genera". However, what can occur is enhancing existing "Nimbostratus" or "Altostratus" due to the additional water vapor or condensation nuclei emitted by a thermal power plant, for instance.
Cloud physics
Clouds in the troposphere, the atmospheric layer closest to Earth, are classified according to the height at which they are found, and their shape or appearance. There are five "forms" based on physical structure and process of formation. "Cirriform" clouds are high, thin and wispy, and are seen most extensively along the leading edges of organized weather disturbances. "Stratiform" clouds are non-convective and appear as extensive sheet-like layers, ranging from thin to very thick with considerable vertical development. They are mostly the product of large-scale lifting of stable air. Unstable free-convective "cumuliform" clouds are formed mostly into localized heaps. "Stratocumuliform" clouds of limited convection show a mix of cumuliform and stratiform characteristics which appear in the form of rolls or ripples. Highly convective "cumulonimbiform" clouds have complex structures often including cirriform tops and stratocumuliform accessory clouds.