ATMOSHERE
• The earth's atmosphere is a very thin layer wrapped around a very large planet.
• Two gases make up the bulk of the earth's atmosphere: nitrogen, which comprises 78% of the atmosphere, and oxygen, which accounts for 21%. Various trace gases make up the remainder.
• Based on temperature, the atmosphere is divided into four layers: the troposphere, stratosphere, mesosphere, and thermosphere.
TROPOSPHERE (0 – 12 km)
• Tropo is a Greek word means turn or change
• It begins at the surface and extends to between 7 km (23,000 ft) at the poles and 17 km (56,000 ft) at the equator
• Contains 75% of the gases in the atmosphere.
• The temperature drops about 6.5 degrees Celsius for every kilometer above the earth's surface.
• Normal weather and clouds occur
• Heating of the Surface creates warm air at surface
• Warm air rises, but air expands as it rises and cools as it expands (Adiabatic cooling)
• Heating + Adiabatic Cooling = Warm air at surface, cooler air above
• Tropopause - located at the top of the troposhere. The temperature remains fairly constant here. This layer separates the troposphere from the stratosphere
STRATOSPHERE (12 – 50 km)
• Latin word "stratus" meaning spreading out.
• The temperature remains fairly constant (-60 degrees Celsius).
• This layer contains the ozone layer.
• Ozone(O3) acts as a shield for in the earth's surface. It absorbs ultraviolet radiation from the sun. This causes a temperature increase in the upper part of the layer.
MESOPHERE (50 – 80 km)
• Greek word “meso" meaning middle.
• The temperature drops in this layer to about -100 degrees Celsius.
• This is the coldest region of the atmosphere.
• This layer protects the earth from meteoroids. They burn up in this area.
• The boundary between the thermosphere and the mesosphere is named as mesopause.
THERMOSPHERE (above 80 km)
• Contains two regions namely,
• Ionosphere
• Exoshere
• Thermosphere means "heat sphere". The temperature is very high in this layer because ultraviolet radiation is turned into heat.
• Temperatures often reach 2000 degrees Celsius or more.
