Cloud the bottom of the hierarchy. Clouds in the troposphere assume five physical forms based on structure and process of formation. These forms are commonly used for the purpose of satellite analysis. They are given below in approximate ascending order of instability or convective activity. "Non-convective" stratiform clouds appear in "stable" airmass conditions and, in general, have flat sheet-like structures that can form at any altitude in the troposphere. The stratiform group is divided by altitude range into the genera cirrostratus (high-level), altostratus (mid-level), stratus (low-level), and nimbostratus (multi-level). Fog is commonly considered a surface-based cloud layer. The fog may form
Cloud forest 10,000 mm/year and mean temperature between 8 and 20 °C. While cloud forest today is the most widely used term, in some regions, these ecosystems or special types of cloud forests are called mossy forest, elfin forest, montane thicket, and dwarf cloud forest. The definition of cloud forest can be ambiguous, with many countries not using the term (preferring such terms as Afromontane forest and upper montane rain forest, montane laurel forest, or more localised terms such as the Bolivian "yungas", and the "laurisilva" of the Atlantic Islands), and occasionally subtropical and even temperate forests in which similar meteorological conditions