TROPOsphere

The troposphere is the lowest layer of Earth's atmosphere, extending from the surface up to the tropopause, the boundary with the stratosphere. Its thickness varies with latitude and season: roughly 7 to 9 kilometers at high latitudes, about 10 to 12 kilometers in mid-latitudes, and up to 16 to 18 kilometers near the equator. The layer contains the majority of the atmosphere’s mass, roughly 75 to 80 percent, as well as most of the water vapor and aerosols.

In the troposphere, temperature generally decreases with height, at an environmental lapse rate of about 6.5 degrees Celsius per kilometer, though actual rates vary with weather. This cooling fosters convection and vertical mixing, which drive weather systems, cloud formation, and precipitation. The layer is also characterized by turbulent air, wind shear, and jet streams near its upper boundary.

The chemistry of the troposphere includes a mixture of dry air—about 78 percent nitrogen and 21 percent oxygen—along with argon, carbon dioxide, neon, and other trace gases. Water vapor can vary widely by location and season, making the troposphere the principal site of the atmospheric hydrological cycle. Clouds and aerosols within this layer influence albedo and infrared trapping, contributing to climate dynamics.

The tropopause marks the transition to the stratosphere, where temperature tends to increase with height due to ozone heating. The troposphere is studied through radiosondes, aircraft, satellites, and ground-based observations, reflecting its central role in weather, climate, and atmospheric science. The term troposphere derives from Greek tropos, turning, and sphaira, sphere, reflecting convective motion in this layer.