ch 17 the atmosphere

THE ATMOSPHERE

Composition of the Atmosphere• The Earth’s atmosphere sustains life, forms a

protective shield that filters out harmful radiation, and protects the Earth from the constant shower of small meteors.

• The atmosphere consists of gases and trace amounts of suspended particles from volcanoes, nuclear explosions, and industrial pollutants.

• 99% of the gases occur within 20 miles above the surface of the earth.

• The most abundant gas is nitrogen (78.1%), followed by oxygen (20.9%), argon (.9%), carbon dioxide (.03%).

• Water vapor is a variable component of the atmosphere, from 0.05% to 4%.

• Ozone is continuously being produced in the Earth’s atmosphere by the interaction of the Sun’s radiant energy with oxygen molecules.

• O2 + energy → 2 O• O2 + O → O3• Ozone is concentrated in the stratosphere.

Ozone absorbs ultraviolet radiation from the sun.• Primary pollutants of the atmosphere are

nitrogen oxides from fuel combustion, volatile organic compounds, sulfur oxides, particulates, and carbon monoxide.

• Secondary pollutants are acid rain and photochemical smog.

2. Changes in Pressure in the Atmosphere

• Pressure is created by the weight of the air above pushing down. Air pressure decreases with height.

Structure of the Atmosphere Troposphere – means “turning over,” • Contains about 80% of all the mass of the

atmosphere and extends from ground level to 8 to 18 km

• Thickest near the equator and thinnest at the poles

• All weather occurs in troposphere• Pressure and temperature decreases in

the troposphereTropopause – boundary between the troposphere

and the overlying stratosphere, important in the formation of the jet stream

Stratosphere – to smooth out, above the height of most clouds, to an altitude of about 30 miles

• Very stable with very little turbulence• Temperature increases in the stratosphere• 79% nitrogen, 20% oxygen and 90% of all

atmospheric ozone• Ozone makes up .001% of the molecules of gas,

yet is vital for life on Earth• Ozone helps prevent harmful ultraviolet radiation

from reaching the earth’s surface

Mesosphere – the layer where incoming meteors first begin to burn

• Temperature decreases, the coldest layer as low as -148 oF

Thermosphere (62 miles), also called the ionosphere

• Air is very thin• Solar wind bombards gas molecules• During high sunspot activity the temperature can

rise as high as 2237 oF and in low sunspot activity 437 oF

• Radio waves bounce off the ionosphere• Electrical disturbances in the ionosphere form

the auroras

4. Earth’s Motions

• Rotation – daily cycle of sunlight and darkness

• Revolution – movement of the Earth around the sun, 113,000 km/hr

• The Earth is closest to the sun in winter, farthest in summer

• Summer solstice – longest day in the Northern Hemisphere, Earth tilted toward the sun

• Winter solstice – shortest day in the Northern Hemishere, Earth is tilted away from the sun

• Equinoxes ( Spring or Fall) – 12 hours of daylight and 12 hours of night everywhere on Earth

5. Earth’s Tilt, 23.5 degreesThe tilt of the Earth is the reason for the seasons

6. Length of Daylight• The length of daylight in the Northern

Hemisphere is greater than the length of darkness in summer. The farther north you go, the longer the period of daylight. On the summer solstice on the Arctic circle the length of daylight is 24 hours!

7. Heat is the transfer of energy due to temperature differences, heat flows from hotter to colderConduction – transfer of heat energy through matter by molecular motion

Convection – transfer of heat energy by the mass movement of matter

Convection is important in distributing heat energy from the tropics to the poles

Convection takes place in the mantle, in water, and in the atmosphere

Radiation – radiant energy that travels through outer space in the form of electromagnetic radiation

8. Solar RadiationWhen radiation strikes an object some of the radiation can be absorbed, some can be transmitted, and some may be reflected.The blue sky s a result of scattering.About 50% of the incoming radiation is absorbed.

9. Greenhouse Effect – water vapor and carbon dioxide absorbs the longer wavelengths re-emitted by the earthNecessary to make life suitable on Earth

10. Variations in TemperatureLatitude – the tropics are warmer and the poles

are colderIsotherms are lines that connect points of equal temperatureIsotherms run from east to west

Land and water – areas by large bodies of water experience more moderate changes in temperature throughout the year. In addition, the range daily highs to daily lows will not be as great as in areas surrounded by land.

Geographic position – a city with the prevailing wind blowing from the ocean will experience cooler, wetter climates than a coastal community with the prevailing wind blowing from the land

Altitude – increasing in altitude is similar to increasing in latitude, the higher the attitude, the colder the climate

Albedo is the fraction of total radiation reflected by any surface. Darker objects have a lower albedo than lighter objects.Clouds have a high albedo and reflect sunlight back into space. At nighttime clouds act as a blanket and have a warming effect.