|
|
|
Earth's Atmosphere
From Wikipedia, the free encyclopedia.
Temperature and the atmospheric layers
|
 | troposphere - 0 - 7/17 km, temperature decreasing with height. |
| stratosphere - 7/17 - 50 km, temperature increasing with height. |
| mesosphere - 50 - 80/85 km, temperature decreasing with height. |
| thermosphere - 80/85 - 640+ km, temperature increasing with height. |
Click the image for a large, clear diagram from NASA
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.
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).
The density of air at sea level is about 1.2 kilograms per cubic meter. This density decreases at higher altitudes at the same rate that pressure decreases. The total mass of the atmosphere is about 5.1 × 1018 kg, a tiny fraction of the earth's total mass.
Atmospheric regions are also named in other ways: Investigate these further if you like.
| 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. |
| 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. |
| 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. |
| Van Allen radiation belts - regions where particles from the Sun become concentrated. |
From Wikipedia, the free encyclopedia.
The troposphere is the lowermost portion of Earth's atmosphere and the one in which clouds and most other weather phenomena occur. This layer extends to an altitude of 16-18 km over tropical regions, decreasing to less than 10 km over the poles, and contains approximately 80% of the total air mass. Generally, jets fly near the top of this layer. The troposphere is directly below the stratosphere.
The troposphere is divided into six zonal flow regions, called cells. These are responsible for atmospheric circulation, and produce the prevailing winds.
The word troposphere stems from the Greek "tropos" for "turning" or "mixing". This region, constantly in motion, is the densest layer. Nitrogen and oxygen are the primary gases within this region. The change of temperature with height is larger than in other layers, the temperature decreasing with altitude.
The tropopause marks the limit of the troposphere and the beginning of the stratosphere. The temperature above the tropopause increases slowly with height up to about 50 km.
The stratosphere is the layer of Earth's atmosphere which, at the equator, is situated between about 17 km and 50 km altitude above the surface, while at the poles it starts at about 8 km altitude due to the lower tropopause height caused by the lower tropospheric temperature there.
The stratosphere sits directly above the troposphere and directly below the mesosphere. Within this layer, temperature increases as altitude increases; the top of the stratosphere has a temperature of about 270 K. This top is called the stratopause, above which temperature again decreases with height.
The stratosphere is a region of intense interactions among radiative, dynamical, and chemical processes, in which horizontal mixing of gaseous components proceeds much more rapidly that vertical mixing. The stratosphere is warmer than the upper troposphere, primarily because of a stratospheric ozone layer that absorbs solar ultraviolet radiation.
An interesting feature of stratospheric circulation is the quasi-Biennial Oscillation (QBO) in the tropical latitudes, which is driven by gravity waves that are convectively generated in the troposphere. The QBO induces a secondary circulation that is important for the global stratospheric transport of tracers such as ozone or water vapor.
In northern hemispheric winter, sudden stratospheric warmings can often be observed which are caused by the absorption of Rossby waves in the stratosphere.
The mesosphere is that layer, of the Earth's atmosphere, which is directly above the stratosphere and directly below the thermosphere. The mesosphere is located 50-80/85km above Earth's surface. Within this layer, temperature decreases with increasing altitude.
Temperatures in the upper mesosphere fall as low as 200K, varying according to latitude and season. Millions of meteors burn up daily in the mesosphere as a result of collisions with some of the billions of gas particles contained in that layer. The collisions create enough heat to burn the falling objects long before they reach the ground.
The stratosphere and mesosphere are referred to as the middle atmosphere. The mesopause, at an altitude of about 80 km, separates the mesosphere from the thermosphere--the outermost layer of the Earth's atmosphere.
The thermosphere is that layer, of the Earth's atmosphere, which is directly above the mesosphere and directly below the exosphere. Within this layer, ultraviolet radiation causes ionization. (see also: ionosphere)
The thermosphere, from the Greek thermo for heat, begins about 80 km above the Earth. At these high altitudes, the residual atmospheric gases sort into strata according to molecular mass. Thermospheric temperatures increase with altitude due to absorption of highly energetic solar radiation by the small amount of residual oxygen still present. Temperatures can rise to 2,000°C. Radiation causes the scattered air particles in this layer to become charged electrically (see ionosphere), enabling radio waves to bounce off and be received beyond the horizon. At the exosphere, beginning at 500 to 1,000 km above the Earth's surface, the atmosphere blends into space. The few particles of gas here can reach 2,500°C (4500°F) during the day.
