globe.gif (1715 bytes) Earth's Atmosphere

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The Troposphere

| Report | Fact Sheet | Test | Answers | FAQ |


The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth. The troposphere is bonded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on bottom by the surface of the Earth. The troposphere is wider at the equator (10mi) than at the poles (5mi).

The troposphere contains 75 percent of atmosphere's mass- on an average day the weight of the molecules in the air is14.7 lb..(sq. in.)- and most of the atmosphere's water vapor. Water vapor concentration varies from trace amounts in Polar Regions to nearly 4 percent in the tropics. Most prevalent gases are nitrogen (78 percent) and oxygen (21 percent), with the remaining 1- percent consisting of argon, (.9 percent) and traces of hydrogen ozone ( a form of oxygen), and other constituents. Temperature and water vapor content in the troposphere decrease rapidly with altitude. Water vapor plays a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet's surface.

The troposphere contains 99% of the water vapor in the atmosphere. Water vapor concentrations vary with latitudinal position(north to south). They are greatest above the tropics, where they might be as high as 3% and decrease toward the polar regions

Carbon dioxide is present in small amounts, but its concentration has nearly doubled since 1900.Like water vapor, carbon dioxide is a greenhouse gas which traps some of the Earth's heat close to the surface and prevents its release into space. Scientists fear that the increasing amounts of carbon dioxide could raise the Earth's surface temperature during the next century, bringing significant changes to worldwide weather patterns. Such changes may include a shift in climatic zones and the melting of the polar ice caps, which could raise the level of the world's oceans.

The uneven heating of the regions of the troposphere by the sun ( the sun warms the air at the equator more than the air at the poles )causes convection currents, large-scale patterns of winds that move heat and moisture around the globe. In the Northern and Southern hemispheres, air rises along the equator and subpolar ( latitude about 50 to about 70 north and south ) climatic regions and sinks in the polar and subtropical regions. Air is deflected by the Earth's rotation as it moves between the poles and equator, creating belts of surface winds moving from east to west ( easterly winds ) in tropical and polar regions, the winds moving from west to east ( westerly winds ) in the middle latitudes. This global circulation is disrupted by the circular wind patterns of migrating high and low air pressure areas, plus locally abrupt changes in wind speed and direction known as turbulence.

A common feature of the troposphere of densely populated areas is smog, which restricts visibility and is irritating to the eyes and throat. Smog is produced when pollutants accumulate close to the surface beneath an inversion layer ( a layer of air in which the usual rule that temperature of air decreases with altitude doesn't apply ), and undergo a series of chemical reactions in the presence pollutants from escaping into the upper atmosphere. Convection is the mechanism responsible for the vertical transport of heat in the troposphere while horizontal heat transfer is accomplished through advection.

The exchange and movement of water between the earth and atmosphere is called the water cycle. The cycle, which occurs in the troposphere, begins as the sun evaporates large amounts of water from the earth's surface and the moisture is transported to other regions by the wind. As air rises, expands, and cools, water vapor condenses and clouds develop. Clouds cover large portions of the earth at any given time and vary from fair weather cirrus to towering cumulus clouds. When liquid or solid water particles grow large enough in size, they fall toward the earth as precipitation. The type of precipitation that reaches the ground, be it rain, snow, sleet, or freezing rain, depends upon the temperature of the air through which it falls.

As sunlight enters the atmosphere, a portion is immediately reflected back to space, but the rest penetrates the atmosphere and is absorbed by the earth's surface. This energy is then remitted by the earth back into atmosphere as long-wave radiation. Carbon dioxide and water molecules absorb this energy and emit much of it back towards the earth again. This delicate exchange of energy between the earth's surface and atmosphere keeps the average global temperature from changing drastically from year to year.

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Fact Sheet

  1. The troposphere contains 75% of the atmosphere's total mass

  2. In either space or time the troposphere is not constant

  3. Weather occurs in the troposphere

  4. The troposphere is 10 miles from the equator

  5. The troposphere is 5-7 miles above the poles

  6. Does not contain ozone

  7. The altitude of the tropopause at the poles is 5 miles

  8. The temperature in the troposphere can reach -80*C

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Troposphere Test

  1. The troposphere contains ozone. True or False

  2. the troposphere can reach               .




  3. What percentage of the total mass of the atmosphere does the troposphere contain?

  4. How high is the troposphere from the equator?

  5. What occurs in the troposphere?

  6. The height of the tropopause ceiling is not constant in time or space. True or False

  7. The altitude of the troposphere from the poles is                            .

    A.3 miles

    B.5 miles

    C.16 miles

  8. The troposphere is                       miles above earth.





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Answers To Test

  1. False

  2. C

  3. 75%

  4. 10 miles

  5. weather

  6. true

  7. B

  8. C

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  1. What goes on in the troposphere?

  2. What's so important about the troposphere?.
    it contains weather and the oxygen that we breath

  3. Is the troposphere the largest atmosphere?

  4. How big is the troposphere?
    It extends 5 to 7 miles above the earth

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