Earth's atmosphere
Earth's atmosphere is a layer of gases surrounding the planet Earth and retained by the Earth's gravity. It contains roughly 78% nitrogen and 21% oxygen, with trace amounts of other gases. This mixture of gases is commonly known as air. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation and reducing temperature extremes between day and night.
The atmosphere has no abrupt cut-off. It slowly becomes thinner and fades away into space. There is no definite boundary between the atmosphere and outer space. Three-quarters of the atmosphere's mass is within 11 km of the planetary surface. In the United States, persons who travel above an altitude of 50.0 miles (80.5 km) are designated as astronauts. An altitude of 120 km (75 mi or 400,000 ft) marks the boundary where atmospheric effects become noticeable during re-entry. The Karman line, at 100 km (62 mi), is also frequently used as the boundary between atmosphere and space.
Temperature and the atmospheric layers
The temperature of the Earth's atmosphere varies with altitude; the mathematical relationship between temperature and altitude varies between the different atmospheric layers:
troposphere: From the Greek word "tropos" meaning to turn or mix. The troposphere is the lowest layer of the atmosphere starting at the surface going up to between 7 km at the poles and 17 km at the equator with some variation due to weather factors. The troposphere has a great deal of vertical mixing due to solar heating at the surface. This heating warms air masses, which then rise to release latent heat as sensible heat that further buoys the air mass. This process continues until all water vapor is removed. In the troposphere, on average, temperature decreases with height due to expansive cooling.
stratosphere: from that 7–17 km range to about 50 km, temperature increasing with height.
mesosphere: from about 50 km to the range of 80 km to 85 km, temperature decreasing with height.
thermosphere: from 80–85 km to 640+ km, temperature increasing with height.
The boundaries between these regions are named the tropopause, stratopause, and mesopause.
The average temperature of the atmosphere at the surface of earth is 14 °C.
Various atmospheric regions
Atmospheric regions are also named in other ways:
ionosphere – the region containing ions: approximately the mesosphere and thermosphere up to 550 km.
exosphere – above the ionosphere, where the atmosphere thins out into space. This is the last major atmosphere.
magnetosphere – the region where the Earth's magnetic field interacts with the solar wind from the Sun. It extends for tens of thousands of kilometers, with a long tail away from the Sun.
ozone layer – or ozonosphere, approximately 10 - 50 km, where stratospheric ozone is found. Note that even within this region, ozone is a minor constituent by volume.
upper atmosphere – the region of the atmosphere above the mesopause.
Van Allen radiation belts – regions where particles from the Sun become concentrated.
Pressure
Barometric Formula: (used for airplane flight) barometric formula
Main article: Atmospheric pressure
Nasa mathematical model: NRLMSISE-00
Atmospheric pressure is a direct result of the weight of the air. This means that air pressure varies with location and time, because the amount (and weight) of air above the earth varies with location and time. Atmospheric pressure drops by ~50% at an altitude of about 5 km (equivalently, about 50% of the total atmospheric mass is within the lowest 5 km). The average atmospheric pressure, at sea level, is about 101.3 kilopascals (about 14.7 pounds per square inch).
References:
The thermosphere: a part of the heterosphere, by J. Vercheval.
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