Earth’s Atmosphere Structure, Layers and the Greenhouse Effect
Elevation, Density and Pressure • The atmosphere extends hundreds of kilometers above the Earth.
The weight of the atmosphere’s upper layers pushes down onto its lower layers. • This generates pressure, so air is concentrated (or denser) in the layer closest to Earth...
The Troposphere,or “The Weather Sphere” • From 0 – 18 km, the lowest layer. • Most dense, contains 70 – 80 % of the air • Most weather and clouds occur here. • Elevation and temperature are inversely related.
The Stratosphere, or “Blanket-sphere” • 18 – 50 km elevation. • Little weather occurs here, BUT… • flat stratus clouds in the lower levels & high winds (jet streams) • Elevation and temperature are directly related • Near the top is a thin layer of Ozone (O3) that blocks UV light.
Mesosphere, the “Middle-Sphere” • 50 – 90 km • Very low density • Elevation and temperature are inversely related
Ionosphere • So little density it’s almost “space.” • Consists of ionized gases. • Aurora Borealis occur here.
The Greenhouse Effect • The Atmosphere lets visible light pass through, but absorbs most infrared light.
Light warms the Earth’s surface. The surface radiates infrared energy, which is then absorbed back into the atmosphere.
This absorption/reflection of infrared energy has two effects: • The average temperature rises. • Temperatures are more moderate.
Some gases – such as CO2 and methane -are called “green house gases” because they absorb infrared heat better than other gases. If they increase in the atmosphere, so does the atmosphere’s average temperature.