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The Ozone Layer

Ozone is the answer. Most ozone exists in the stratosphere between about 15 to 20 miles high. It absorbs radiation from the sun, allowing a buildup of heat. On page 161 of Weather, figure 14.2 shows how much colder the stratosphere would be if there was no ozone layer.

When it occurs at ground level, ozone is pollution. But high in the atmosphere, it shields us -- and all life on Earth -- from harmful ultraviolet rays.

Inversions

The tropopause is a planet-wide inversion, acting as a "roof" to weather. It stops the vertical growth of thunderstorms. In Los Angeles, a much smaller-scale inversion also creates a "roof," trapping haze and pollution and blocking the view of the mountains

How High Is the Sky?

How high is the sky anyway? On our field trip through the atmosphere, we've discovered that the air becomes too thin to breathe after only a few miles. At the top of Mount Everest, two-thirds of the atmosphere's mass is below us. By the time we've climbed midway through the stratosphere, already 99 percent of all molecules in the atmosphere are far below us. Hardly any air is left, but we still have three more layers of the atmosphere to visit!

Mesosphere

The mesosphere is next, starting at an altitude of about 50 miles. It's somewhat arbitrarily designated as the beginning of "space." As far as breathing is concerned, you wouldn't be able to tell the difference between the mesosphere and a vacuum. This is the coldest layer of Earth's atmosphere, bottoming out at about --150 degrees Fahrenheit.

Thermosphere

The thermosphere is utterly inhospitable. Temperatures here vary from 1000 degrees to over 3600 degrees Fahrenheit, depending on solar activity. The space shuttle orbits in the thermosphere, with a maximum ceiling of about 300 miles. Technically, at this stage of our tour we're still in the atmosphere (though you wouldn't know it if you tried to step outside the space shuttle without a space suit).

Exosphere

Above about 350 miles lies the exosphere. In lower layers, the composition of the atmosphere is fairly homogenous, meaning that the proportions of nitrogen, oxygen, and other elements stay more-or-less the same. (Only water vapor varies significantly.) But the very top of the atmosphere consists of the lightest elements, hydrogen and helium. High in the exosphere, a lonely atom of hydrogen might travel several miles before bumping into another atom. With all that empty room, the light elements accelerate, picking up so much velocity that they escape into space.


Date: 2014-12-28; view: 874


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