Welcome to You Ask Andy

Danny Brooks, age 14, of Monroe, North Carolina, for his question:

How are the layers of the atmosphere determined?

In one respect, the layers of the atmosphere are misleading. They seem to suggest neatly separated pages of paper, when actually the filmy air merges from one layer to the next. Generally, each layer can. be identified from its numbers and types of particles together with its main type of energy. But these general factors are governed by dynamic forces from the earth below and from outer space above the airy shell. These forces fluctuate, causing atmospheric upheavals that blur the boundary lines.

Early mountaineers found that the air grew thinner as they ascended. Later researchers weighed the pressure of the atmosphere and figured that about half its gases are packed below about 3 1/2 miles above the surface. Daredevil balloonists of the 19th century explored the weather a few miles upstairs. They found winds blowing contrary to those at ground level, plus other surprises.

During the following decades, the upper air was explored by blimps, planes and more sophisticated weather balloons. As the picture took shape, the atmosphere appeared to be a sort of multiple sandwich of airy shells, stacked in different layers, each with definite characteristics of its own. To a large extent this is true. Our weather events are crowded into the lowest troposphere layer. However, highflying planes found wild jet stream winds in the supposedly weatherless layer above the troposphere.

The desire to probe the upper atmosphere helped to trigger the Space Age and Space Age satellites have relayed fantastic data from way out to the Van Allen belts and beyond. We now know that the upper levels of thinning air are energized by cosmic forces, including solar winds and solar radiations. These dynamic onslaughts fluctuate, punch dents in the multiple sandwich and distort its layers.

Obviously, the earth's gravity hugs the densest airy layer to the surface and partially governs the thinning layers above. But at present, researchers are evaluating fascinating new evidence about the earth's magnetic field    its relationship to outer cosmic forces and its possible effects on various layers of the atmosphere.

The calm cool stratosphere reaches up from roughly five to 50 miles. We now know that it contains a thin sulphate layer and a wider ozone layer, where most of the oxygen is in energetic molecules of ozone. This layer absorbs and filters out the dangerous ultraviolet from solar radiation. Near the top of the stratosphere, layers of dust and other particles form a wide streaky boundary with the ionosphere. This immense realm of charged ions triggers auroras and bounces back our radio beams. Gradually the temperature rises to 2000 degrees Fahrenheit and the ionosphere merges with the exosphere. There the thin gases finally peter out and the atmosphere loses itself in space.

A few decades ago, we pictured the atmosphere in neat layers. To some extent this is true. In general, the different characteristics and functions of each layer can be defined. But the boundaries between them merge and fluctuate. More about these factors will be learned from current research in the earth's tricky magnetic field and its relationship to various dynamic forces that constantly bombard our planet.

 

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