The Stratosphere and Ozone Layer
Investigating the Layered Structure of the Earth’s Atmosphere
Sep 20, 2009
Located between the thick troposphere below it and the rarified mesosphere above it, the stratosphere (from the Greek stratos meaning to “smooth out”) is a layer of thin but very stable air with limited turbulence, except at times of solar storms.
Located above the heights of most clouds, there is no vertical mixing of the air thus there is no wind or weather there. There is, however, a horizontal mixing of the gaseous components of the stratosphere.
The Height of the Stratosphere
The stratosphere stretches from the top the tropopause below it upwards to an altitude of about 10 km (6 mi) to 50 km (30 mi) at mid-latitudes to about 8 km (5 mi) at the poles.
Commercial airliners often cruise in the lower stratosphere which allows them to avoid harsh weather and air turbulence. Furthermore, jet engines work more efficiently at the lower temperatures found in the stratosphere.
The Temperature of the Stratosphere
The temperature of the air actually increases with altitude within the stratosphere. This is in direct opposition to the troposphere. In the troposphere the air is warmest at the bottom of the layer and gets cooler as you go upward but the stratosphere is coolest at the bottom and gets warmer as you go upward.
Temperatures in the stratosphere range from about -60°C (-76°F) at the bottom of the layer to about 0°C (32°F) at the top of the layer. This increase in temperature is due to the presence of ozone molecules within the stratosphere.
The Ozone Layer
The stratosphere contains 90% of all atmospheric ozone, commonly referred to as the ozone layer. This term is misleading because ozone forms only a very tiny portion of the stratosphere (0.001%) and accounts for only one in every 100,000 molecules of gas. In fact, if all the ozone in the stratosphere was compressed together, it would form a layer of pure ozone only about 3 mm (one-tenth of an inch) thick.
Ozone molecules are structured in such a way that they absorb the harmful ultraviolet rays from the sun. (Normal oxygen consists of two bonded oxygen atoms; ozone consists of three bonded oxygen atoms) This absorption heats the stratosphere causing the dramatic temperature increase from the lower levels to the upper levels of the layer.
There is currently great debate and much research into human-caused ozone depletion. The meteorological concern regarding ozone depletion is the effect such depletion could have on the whole thermal structure of the atmosphere and its ability to retain water.
The Stratopause
The upper reaches of the stratosphere are marked by a boundary between the stratosphere below and the mesosphere above. This boundary is the stratopause and it is distinguished by the fact it is the point at which temperature once again begins to diminish with increasing altitude.
Out of sight and out of mind high above the head of humanity, the stratosphere forms a life-saving shield. While some bacterial life may actually reside in the stratosphere, it is the ozone within the stratosphere that absorbs deadly ultraviolet radiation from the sun. Without this ozone shield, life at the surface would have fried away long ago.
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