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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.

2006-10-11 08:12:18 · answer #1 · answered by Otis F 7 · 2 2

The tropopause is a boundary region in the atmosphere between the troposphere and the stratosphere.

The troposphere is the lowest of the Earth's atmospheric layers and is the layer in which all of what we call "weather" occurs. It begins at ground level and ranges in height from an average of 6 km (4 miles) at the poles to 17 km (11 miles) at the equator. At the equator, the stratosphere begins at roughly 17 km (11 miles) in altitude, and it may reach as high as 50 km (31 miles) from the earth's surface. This is also the location of the ozone layer. It is at its highest level over the equator and the lowest over the geographical north pole and south pole. On account of this, the coolest layer in the atmosphere lies at about 17 km over the equator. There are two types of tropopauses, viz. equatorial tropopause, and polar tropopause.

Measuring the lapse rate through the troposphere and the stratosphere identifies the location of the tropopause. In the troposphere, the lapse rate is, on average, 6.5 °C per kilometre. That is to say, for every kilometre in height, the temperature drops by 6.5 degrees Celsius. In the stratosphere, however, the temperature increases with altitude. The region of the atmosphere where the lapse rate changes from positive (in the troposphere) to negative (in the stratosphere), ie, where the temperature no longer decreases with altitude but rather increases, is defined as the tropopause. The exact definition used by the World Meteorological Organization is:

the lowest level at which the lapse rate decreases to 2 °C/km or less, provided that the average lapse rate between this level and all higher levels within 2 km does not exceed 2 °C/km.

Alternatively, a dynamic definition of the tropopause is used with potential vorticity instead of vertical temperature gradient as the defining variable. There is no universally used threshold: the most common ones are: the tropopause lies at the 2 PVU or 1.5 PVU surface. PVU stands for potential vorticity unit. This threshold will be taken as a positive or negative value (e.g. 2 and -2 PVU), giving surfaces located in the northern and southern hemisphere respectively. To define a global tropopause in this way, the two surfaces arising from the positive and negative thresholds need to be joined near the equator using another type of surface such as a constant potential temperature surface.

It is also possible to define the tropopause in terms of chemical composition. For example, the lower stratosphere has much higher ozone concentrations than the upper troposphere, but much lower water vapor concentrations, so appropriate cutoff values of either of these can be used.

The tropopause is not a "hard" boundary. Vigorous thunderstorms, for example, particularly those of tropical origin, will overshoot into the lower stratosphere and undergo a brief (hour-order) low-frequency vertical oscillation. Such oscillation sets up a low-frequency atmospheric wave train capable of affecting both atmospheric and oceanic currents in the region.

2006-10-11 16:37:03 · answer #2 · answered by C-Dubs 2 · 0 0

Tropopause.
It is a place where vertical gas exchange and weathering begin to cease before reaching the stratosphere.

2006-10-11 15:10:28 · answer #3 · answered by ohmneo 3 · 1 0

Tropopause then statosphere. Topopause is where cirrus clouds are

2006-10-13 01:15:50 · answer #4 · answered by Jeramie L 2 · 0 0

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