Weather Atmosphere May 5, 2008

Atmosphere The atmosphere is the layer of air that surrounds Earth like a blanket. It is made up of a mixture of gases plus small amounts of tiny solids and liquids. Composition Nitrogen 78% Oxygen 21% Other 1%

Air Pressure Air surrounding the Earth consists of matter. The Earth’s gravitational pull on the air keeps the atmosphere from drifting off into space. The mass of the upper layers “presses” down on the lower layers squeezing the molecules together.

Temperature in the Atmosphere The temperature of the atmosphere varies. It is most dependent on what the “heat source” for the specific area of the atmosphere is: surface of the earth, ozone layer, or ultraviolet radiation (in combination with the low density of the upper atmosphere)

Temperature is a measure of how fast molecules are moving, and the speed the molecules are moving at is a function of how much energy they absorb. The more energy molecules absorb, the faster they move. The faster the molecules are moving, the higher the temperature. Temperature is a measure of how fast molecules are moving, and the speed the molecules are moving at is a function of how much energy they absorb. The more energy molecules absorb, the faster they move. The faster the molecules are moving, the higher the temperature. The troposphere is warmed by gasses that absorb longwave (terrestrial) radiation. When CO2 and other greenhouse gasses in the troposphere absorb longwave radiation, they move faster causing the troposphere to warm. The farther we are from the earth (the source of longwave radiation that warms the troposphere), the cooler the temperature. The stratosphere is warmed by gasses that absorb shortwave (solar) radiation. Ozone (O3) is very good at absorbing shortwave radiation. The more shortwave (solar) radiation the ozone absorbs, the faster the molecular motion, and the warmer the stratosphere. Temperatures in the stratosphere are highest where the density of ozone molecules is highest. The temperature in the three outermost layers, the mesosphere, thermosphere and exosphere are also a function of the gasses there that are capable of absorbing solar radiation. In the mesosphere, temperature decreases with altitude because as altitude increases, the density of ozone molecules decreases. Since there is less ozone to absorb solar radiation, temperatures decrease. By the time we get to the very outermost layers, the thermosphere and exosphere, molecules of oxygen there absorb a lot of solar radiation, so they're moving at very high speeds (i.e. the temperature is high), however, there are very very few molecules of oxygen (or anything else) in these outermost layers. If we could travel to the thermosphere and exosphere and step outside, it would feel very very very cold. That's because there are so few molecules there, that we wouldn't feel any warmth, despite the fast rate at which the molecules are moving. So, the temperature structure of these outermost layers is kind of deceptive; it really wouldn't feel warm at all even though the molecules are moving very fast.

Closure What is the atmosphere? What is the atmosphere’s composition? How is air pressure formed? What is temperature? What determines the temperature of the atmosphere?

Assignment Atmosphere Assignment