Definition (Encyclopedia of Global Warming)
The mesosphere is the region of the atmosphere extending from the top of the stratopause (about 50 kilometers high) to the bottom of the mesopause-lower thermosphere boundary (MLT), about 100 kilometers high. It is the coldest region of the atmosphere. The warmest temperatures in the mesosphere are found just above the stratopause, where air temperatures may be as high as -5° Celsius. Mesospheric temperatures decrease with increasing altitude, with the lowest temperatures, around -125° Celsius, occurring during summer at the mesopause.
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Significance for Climate Change (Encyclopedia of Global Warming)
The natural source of water in the mesosphere is oxidation of methane. Atmospheric concentrations of the greenhouse gas (GHG) methane have increased dramatically since the beginning of the Industrial Revolution and may have influenced the appearance of noctilucent clouds. Water vapor emitted by rockets and the Space Shuttle has been observed to form noctilucent clouds. Exhaust from one shuttle mission may increase the appearance of noctilucent clouds by as much as 20 percent. Carbon dioxide (CO2) in the mesosphere releases heat to space. Solar proton events have been observed to cool the lower mesosphere by causing photochemical reactions leading to ozone depletion, causing an estimated temperature drop of up to 3° Celsius.
Gravity waves are the dominant form of motion in the mesosphere, with wavelengths of around 10 kilometers. Wind speeds on the order of 100 meters per second may occur in the MLT. Gravity wave flux is lowest at solar maximum. Direction of atmospheric transport is from the summer hemisphere to the winter hemisphere.
In the mesosphere, clouds can form only at the coldest temperatures, within about thirty days of the summer solstice at latitudes above 50° north and below 50° south. Because they form at 82 kilometers altitude, the thin filamentous noctilucent clouds (sometimes called polar mesospheric clouds, or PMCs) are illuminated only when the Sun is between 6° and 16° below the...
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Further Reading (Encyclopedia of Global Warming)
Arnold, Neil. “Solar Variability, Coupling Between Atmospheric Layers, and Climate Change.” Philosophical Transactions of the Royal Society of London A 360, no. 1801 (December, 2002): 2787-2804. Reprinted in Advances in Astronomy, edited by J. M. T. Thompson. Vol. 1. London: Imperial College Press, 2005. Excellent technical survey of the relationship between solar activity and the atmosphere, including the mesosphere, suggesting a mechanism for solar influences in the mesosphere to influence the climate in the troposphere.
Bellan, Paul M. “Ice Iron/Sodium Film as Cause for High Noctilucent Cloud Radar Reflectivity.” Journal of Geophysical Research D 113 (2008): 16,215-16,218. Advances a hypothesis as to why noctilucent clouds show up on radar.
Glickman, Todd S., ed. Glossary of Meteorology. 2d ed. Boston: American Meteorological Society, 2000. This standard reference book contains definitions of meteorological terms, such as the mesosphere.
Schroeder, Wilfried, and Karl-Heinrich Wiederkehr. “Johann Kiessling, the Krakatoa Event, and the Development of Atmospheric Optics After 1883.” Notes and Records of the Royal Society of London 54, no. 2 (May, 2000): 249-258. Briefly discusses the discovery of noctilucent clouds following the eruption of Krakatoa.
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Mesosphere (World of Earth Science)
Based on the vertical temperature distribution in Earth's atmosphere, four semi-horizontal layers or "spheres" can be distinguished: the troposphere, stratosphere, mesosphere, and thermosphere,. These layers are separated by "pauses," where no change in the temperature occurs with altitude change: the tropopause (between the troposphere and the stratosphere), the stratopause (between the stratosphere and the mesosphere), and the mesopause (between the mesosphere and the thermosphere). The stratosphere and mesosphere together are called the middle atmosphere, and their region also overlaps with the ionosphere, which is a region defined on the basis of the electric charges of the particles there.
The mesosphere, which means middle sphere, is the third layer of Earth's atmosphere, between the stratosphere, and the thermosphere. It is located from about 55 kilometers (35 miles) to 85 kilometers (54 miles) above the surface of Earth. Temperature here decreases with height, so within the mesosphere it is warmest at its lowest level (°C, or 23°F), and becomes coldest at its highest level (0°C, or 12°F). Depending on latitude and season, temperatures in the upper mesosphere can be as low as 40°C (20°F). The temperature in the mesosphere is lower than the temperature of the troposphere or stratosphere, which makes the mesosphere the coldest among the atmospheric layers. It is colder then Antarctica's lowest recorded temperature, and it is cold enough to freeze water vapor into ice clouds, which can be seen mostly after sunset.
Although the air in the mesosphere is relatively mixed, it is very thin, resulting in low atmospheric pressure. At this height, not only concentrations of ozone and water vapor are negligible, air in the mesosphere contains much less oxygen than in the troposphere. The mesosphere is also the layer in which many meteors burn up when they enter the earth's atmosphere, as a result of the collision with some of the gas particles present in this layer.
See also Atmospheric composition and structure; Stratosphere and stratopause; Thermosphere