Troposphere: region of mixing The Troposphere is the lowest layer of Earth's atmosphere, extending from the surface up to an average height of ≈ 11 kilometres. It contains approximately 75-80% of the atmosphere's mass, with 99% of the Earth's water vapor concentrated in this layer. All weather events, including clouds, rain, and storms, occur within the troposphere. Height : Vary with ◈ Latitude – ≈ 16 km at the equator and around 6 km at the poles. ◈ Seasonal – Generally higher in summer and lower in winter. Tropopause Tropopause : This is the boundary layer between the troposphere and stratosphere, typically about 1.5 km thick, where mixing of air stops. The temperature at the tropopause is much lower at the equator (around – 80°C at about 17 km) compared to the poles (approximately -45°C at around 8-9 km) due to the lapse rate of about 6.5°C/km. Its height also affected by the latitude and seasonal change. Temperature and height profiles for tropical, mid-latitude and polar regions. Stratosphere: weather-free zone The Second Layer of Earth's atmosphere, situated above the troposphere and extending up to about 50 kilometres in altitude. Unlike the troposphere where temperature decreases with altitude, the stratosphere experiences a gradual temperature increase. This phenomenon is primarily attributed to the presence of the Ozone Layer, which absorbs harmful ultraviolet radiation from the sun and converts it into heat. Temperature gradually increases with height, reaching approximately 0°C at an altitude of 50 Km (upper boundary). Clouds and Moisture : The lower stratosphere may occasionally host Cirrus Clouds. Largely free from weather phenomena like storms (turbulence) and clouds, making it an ideal region for aircraft operations. Polar vortex It is a large area of Low Pressure and an Intensely Rotating Cold–Air–Mass surrounding both of Earth's poles, primarily the North Pole. This rotating air generally remains stable, but during autumn, when temperatures drop sharply due to the onset of the polar night, a strong temperature contrast forms between the poles and the tropics, driving the formation of cyclonic winds. Stable and disrupted polar vortex, as illustrated in the chapter. Types of polar vortex Tropospheric Polar Vortex : Located at lower altitudes (up to 10-15 km), this vortex is present year-round, but it is strongest during the winter. Stratospheric Polar Vortex : Found between 15 and 50 km in altitude, this vortex is most intense during the winter, leading to a rapid drop in temperatures in both the Arctic and Antarctic regions. Quick revision The troposphere contains most atmospheric mass and almost all water vapour described in the chapter.Tropospheric height varies with latitude and season.Stratospheric temperature increases with height through ozone absorption of ultraviolet radiation.The chapter distinguishes tropospheric and stratospheric polar vortices. Related concepts from Chapter 1Abiotic components of environmentPhotosynthesis and biotic–abiotic interactionsThe interdisciplinary nature of environmental scienceRelated topicsStructure of Atmosphere: Layers, Exosphere, Homosphere and HeterosphereOzone: Formation, Depletion and Effects on PlantsChapter 2 indexComposition of Atmosphere: Gases, Water Vapour and DustStructure of Atmosphere: Layers, Exosphere, Homosphere and HeterosphereTroposphere, Stratosphere and Polar VortexOzone: Formation, Depletion and Effects on PlantsMesosphere: Noctilucent Clouds, Meteors and Gravity WavesThermosphere and Ionosphere: Temperature and Radio CommunicationAurora and Magnetosphere: Solar Wind and Earth’s Magnetic FieldSodium Layer: Artificial Guide Stars and Adaptive Optics
