2 important functions served by our atmosphere are: it protects Earth’s surface from the sun’s radiation AND it helps regulate the temperature of Earth’s surface. • Without our atmosphere, we would likely die from radiation or heat.
Composition of the Atmosphere • Permanent: • Nitrogen-78% • Oxygen-21%, • Others - 1% • Variable: • Water vapor (H2O) • Carbon dioxide (CO2) • Ozone (O3) • Particulates (dust & pollution)
Oxygen comprises 21% of Earth’s atmosphere. • Natural processes maintain the chemical balance of oxygen in the atmosphere. • Oxygen is continuously being cycled. • 6 ways oxygen is removed from the atmosphere • 1. Animals, 2. bacteria, 3. plants remove it for life processes • 4. Fires, 5. burning fuel, 6. chemical weathering of rocks
Parts of Atmosphere important to weather Water Vapor - as water evaporates from oceans, lakes, streams, and soil, it enters air as water vapor. Transpiration -the life process by which plants and animals give off water vapor Condensation & precipitation -removes water vapor as it enters the atmosphere
3 factors that affect the percentage of water vapor in the air • Time of day • Location • Season • Dry air has less than 1% water • Moist air may contain up to 4% water
Ozone • Ozone high in the atmosphere is good • Absorbs harmful UV rays • Ozone here is formed naturally • 3 oxygen molecules = O3 • CFC’s break down good ozone and cause the hole in the ozone layer. This allows more of the sun’s radiation to heat the earth (global warming)
- Ozone low in the atmosphere is bad • creates smog • made by humans
Particulates - Volcanic dust, ash from fires, pollen - Absorb water and helps to form clouds - Absorbs/reflects sunlight
Atmospheric Pressure Holds gases of the atmosphere near Earth’s surface. The weight of the air above a point . Exerted equally in all directions. Measured with a barometer Standard Atmospheric Pressure = 1 atm or 760 mm of mercury or 1000mb
Earth’s gravity keeps 99% of the total mass of the atmosphere within 32km of Earth’s surface. • Because the pull of gravity is not as strong as it is at higher altitudes, the air molecules are farther apart and exert less pressure. • ***This is why atmospheric pressure changes with altitude!** • As altitude increases, pressure decreases.
Besides altitude, two other factors that can cause changes in air pressure: • Differences in temperature • Amount of water in the air • At sea level, when temperature increases, pressure decreases. • Water molecules have less mass than nitrogen or oxygen. When air has a lot of water vapor in it, the mass of the water is less than the nitrogen/oxygen it displaced. This is why moist air is less dense than dry air is.
Atmospheric pressure variation with altitude
Measuring Pressure Mercurial Barometer -Tube filled with mercury -air pressure pushes on mercury from bottom -causes mercury to rise and fall
Aneroid Barometer • Metal expands and contracts with changes in pressure • Causes pointer to move so pressure can be read
Barograph • Recording aneroid barometer • Keeps track of pressure over several days
Troposphere • Weather Sphere • Lowest Layer • Temperature decreases with height at constant rate • Most clouds • Most water vapor • Most airplanes fly here • TROPOPAUSE: upper boundary of troposphere
Stratosphere • Ozone Layer • Found between troposphere and mesosphere • Increase Temp with height because ozone absorbs UV • STRATOPAUSE – upper boundary of stratosphere
Mesosphere • Coldest layer of atmosphere • Temperature decreases to coldest point at the mesopause (upper boundary of mesosphere) • (-90⁰C) • Many meteors burn up in this layer.
Thermosphere • Air is very thin. - Uppermost layer of atmosphere • Temperature increases due to absorption of solar energy by nitrogen and oxygen • Satellites orbit here • MESOPAUSE: lower region of thermosphere
Ionosphere – part of the thermosphere • Electrically charged layer • AM radio waves reflect off of here • Causes auroras – phenomena caused by interactions between solar radiation & ionosphere