Environmental Systems Topic 5: Atmosphere A.S.: A – G

Review of the Atmosphere The atmosphere is the thin layer of gases that surrounds the earth. What are the layers of Earth’s atmosphere?

Atmospheric Structure - Troposphere Troposphere: the innermost layer; extends about 17 kilometers (11 miles) above sea level at the equator and 8 kilometers (5 miles) at the poles. 75% of air molecules are in this one layer All the weather that affects us takes place here (lots of water vapor) – Causes the Albedo Effect = The Greenhouse Effect takes place in the Troposphere What is the purpose of the GH Effect? Clean air is composed of 78 % Nitrogen 21% Oxygen 1% is made up of CO2 , CH4 and Ar. The top of the troposphere is a zone called the tropopause (this is a transition zone, not a layer, to the next layer).

Temperature & Pressure Profiles in the Troposphere Pressure decreases with altitude (as you go up) because there are less gasses as you go up. Temperature declines with altitude (this is called the lapse rate).

Atmospheric Structure - Stratosphere Second layer: 17-48 kilometers (11-30 miles) above sea level Contains less matter than troposphere Composition similar to troposphere with 2 exceptions 1000 times less water vapor 1000 times more ozone (O3) The Ozone Layer is found at the bottom of the Stratosphere; blocks harmful UV rays from reaching Earth’s surface. Trends - pressure decreases to zero and temperature increases (because of the ozone absorbing sun rays) until outer zone of stratosphere which is called the stratopause.

3rd & 4th Layers Thermosphere: 4th layer; 80 kilometers (50 miles & up) Temperature rises to over 120o C because of N2 and O2 absorb solar energy. Pressure stays at 0 Mesosphere: 3rd layer; 50-80 kilometers (30-50 miles) above sea level Temperature decreases to around -60 deg C while pressure remains 0. Ends at Mesopause

Temperature and Pressure changes as you go through the atmospheric layers.

Transfer of Heat Why isn’t the Earth heated evenly? The atmosphere balances out these differences by transferring the heat in convection cells. Warm air moves towards the poles Cold air moves towards the Equator This is what the air circulation would look like if the Earth was not rotating.

Tri-Cellular Model The rotating Earth Causes 3 Pairs of Cells instead of one pair: Hadley Cells = Ferrel Cells = Polar Cells = Hadley = 0-30 N & S Ferrel = 30-60 N & S Polar Cells = 60-90 N & S

Tri-Cellular Affects on Climate Latitude Relative Temperature & Air Movement (Sinking or Rising) Effects on Climate 0o (Equatorial Low) High Temps cause Warm wet/humid air to rise Rains creating Rainforest Around 30o N&S (Subtropical High) Cooler dry air sinks absorbs moisture Creates Deserts Around 60o N&S (Subpolar Low) High Temps cause Warm wet/humid air to rise. (relative) Creates Temperate Forests Around 90o N&S (Polar High) Cooler dry air sinks absorbs moisture (relative) Creates Tundra (dry but very cold desert!)