One of three height zones (high, middle, and low) into which the troposphere is divided for the purposes of cloud classification. The height is taken as that of the cloud base. High: between c.3–8 km (c.10 000–25 000 ft) in polar regions and c.6–18 km (c.20 000–60 000 ft) in the tropics. Middle: between c.2–4 km (c.6 500–13 000 ft) in polar regions and c.2–8 km (c.6 500–25 000 ft) in the tropics. Low: from the surface to c.2 km (c.6 500 ft) at all latitudes.
Subjects: Meteorology and Climatology.