Homosphere
The homosphere is the layer of an atmosphere where the bulk gases are homogeneously mixed due to turbulent mixing or eddy diffusion. The bulk composition of the air is mostly uniform so the concentrations of molecules are the same throughout the homosphere. The top of the homosphere is called the homopause, also known as the turbopause. Above the homopause is the heterosphere, where diffusion is faster than mixing, and heavy gases decrease in density with altitude more rapidly than lighter gases.
Some of the processes driving this uniformity include heating convection and air flow patterns. In the troposphere, rising warm air replaces higher cooler air which mix gases vertically. Wind patterns push air across the surface mixing it horizontally.[1] At higher altitudes, other atmospheric circulation regimes exist, such as the Brewer-Dobson circulation in the terrestrial stratosphere, which mixes the air. In Earth's mesophere, atmospheric waves become unstable and dissipate, creating turbulent mixing of this region.
Earth's homosphere
The Earth's homosphere starts at the Earth's surface and extends to the turbopause at about 90 km (56 mi).[2] It incorporates all of the troposphere, stratosphere, mesosphere, and the lower part of the thermosphere. Chemically the homosphere is composed of 78% nitrogen, 21% oxygen, and trace amounts of other molecules, such as argon and carbon dioxide.[1] It contains over 99% of the mass of the Earth's atmosphere. The density of air decreases with height in the homosphere.[3] By definition & notably, it also includes a 10 km (6 mi) thick band of elemental mesosphere sodium.[citation needed]
Variations in concentration
One large-scale exception to effective mixing is the
Water vapor concentration (humidity) varies considerably, especially in the troposphere, and is a major component of weather. Water evaporation is driven by heat from incoming solar radiation, and temperature variations can cause water-saturated air to expunge water in the form of rain, snow, or fog. The heat gained and lost by water through these processes increases turbulence in the lower atmosphere, especially at mesoscale and microscale. The Brewer–Dobson circulation is a theory of large-scale ozone circulation.
Concentrations of other trace gases are higher near natural and artificial sources. This includes
References
- ^ a b "OS411B: M2, U1, P3 : The Homosphere". www.shodor.org. Retrieved 2019-06-01.
- ^ "Atmosphere | gaseous envelope". Encyclopedia Britannica. Retrieved 2019-06-01.
- ^ "ATMOSPHERIC COMPOSITION TEMPERATURE AND FUNCTION". web.ccsu.edu. Retrieved 2019-06-01.
- ^ "CHAPTER 10. STRATOSPHERIC OZONE". acmg.seas.harvard.edu. Retrieved 2019-06-09.