17.1 The Atmosphere

Unit 7: Atmosphere, Weather, and Climate  Weather – the state of the atmosphere at a given time vs. vs.  Climate – weather over many years

Most important measurable properties: 1. Temperature 2. Humidity 3. Type and amount of precipitation 4. Air pressure 5. Speed and direction of wind

Composition of atmosphere  A mixture of gases: –Nitrogen 78% –Oxygen 21% –Argon less than 1% –CO 2 less than 1% –Water vapor varies from 1-4%

Volume of Clean, Dry Air

Variable Components / Human Influence  Water vapor is the source of all clouds & precipitation. Water vapor absorbs heat given off by Earth & some solar energy. (Like CO2)  Ozone (O3)  Primary pollutants = emitted directly from identifiable source  Secondary pollutants = not emitted directly into air.

Primary Pollutants

Structure of the Atmosphere  Atmosphere rapidly thins (pressure decreases) as altitude increases (as you travel away from Earth)  Atmospheric pressure is the weight of the air above

Layers of the atmosphere – based on temperature changes  Colder as you climb higher  Divided into 4 layers based on temperature: –Troposphere: bottom layer, temp decreases w/ increase in altitude –Stratosphere: temp. remains constant to height ~20 km then gradually increases (heated…why?) –Mesosphere: temps. decrease w/ height until mesopause. –Thermosphere: contains only tiny amt of the atmosphere’s mass. Temps. Increase

Earth – Sun Relationship  2 main motions –Rotation: spinning on axis –Revolution: movement of Earth in its orbit around the sun  Seasonal changes occur bc Earth’s position to the sun constantly changes as it travels along its orbit  If the axis was NOT tilted we would not have seasonal changes  Axis points to the North Star

 Summer Solstice: 1 st day of summer (NH leaning toward the sun)  Winter Solstice: 1 st day of winter (NH leaning away from the sun)  Autumnal Equinox: Sept. 22 or 23 in NH (occurs halfway btw the solstice)  Spring Equinox: March 21 or 22 in NH (axis neither leaning toward or away from the sun)  Length of daylight = Earth’s position in orbit –Summer = longer daylight

Review/Preview 1.List the layers and boundaries of atmosphere in order from bottom to top. 2.What gas absorbs short wavelength UV radiation? What gases absorb long wavelength radiation? 3.Where are the answers to #2 found? (in which two atmospheric layers?)