Post on 20-Jan-2016
Characteristics of the Atmosphere
The Composition of the Atmosphere
• The atmosphere is made of 78% Nitrogen gas and about 21% oxygen.
• The atmosphere also contains small particles such as dust, volcanic ash, sea salt, dirt, smoke, liquid and solid water
Atmosphere Facts
• The atmosphere is held around the Earth by gravity.
• Air pressure is caused by gravity pulling the gas molecules in the atmosphere toward the Earth’s surface.
Structure of the AtmosphereStructure of the Atmosphere
• The atmosphere is divided into four layers– Troposphere
• The lowest layer is where most of the weather occurs
– StratosphereStratosphere– MesosphereMesosphere– thermospherethermosphere
The Troposphere: The Layer in Which We Live
• Layer we live in• Tropo means “turning” or “change”• Called this because differences in air
pressure and temperature cause gases in the troposphere to move continuously
• Lowest layer• Most dense layer (90% of the atmosphere’s
mass)• All weather occurs in this layer
The Stratosphere: Home of the Ozone Layer
• The atmospheric layer above the troposphere is called the stratosphere.– Strato means “layered”– Very thin with little moisture– Lowest layer is extremely cold (-60° C)– Temperatures rise with altitude because the
ozone layer absorbs UV from the sun– Pilots fly planes here to avoid weather
disturbances and/or on very long flights.
The Mesosphere: The Middle Layer
• The mesosphere is the middle layer of the atmosphere. It is also the coldest layer.– Meso means “middle”– Temperature decreases as altitude increases
(-93°C at the top)
The Thermosphere: The Edge of the Atmosphere
• The uppermost atmospheric layer is called the thermosphere.– Thermo means heat; high temps (1,000° C or
higher) because Nitrogen and Oxygen atoms absorb solar radiation and release thermal energy
– Temperature increases with altitude– Particles move fast but it does not feel hot!– Density so low particles do not collide to
transfer heat
The Ionosphere: Home of the Auroras
• In the upper thermosphere and the lower ionosphere, nitrogen and oxygen atoms absorb harmful solar energy. – Gas particles become electrically charged
(ions) – Can radiate energy as shimmering lights
called auroras
Atmospheric Pressure
• Air Pressure is the measure of the force with which air molecules push on a surface.
• Air pressure decreases as altitude (height) increases
Air PressureAir Pressure
• Is caused by the weight of the atmosphere
• Above each square inch of Earth’s surface is a column of air that weighs 14.7 pounds
Air Pressure FactorsAir Pressure Factors• If air is cooled, it contracts and becomes
denser– This causes pressure to rise
• If air is heated, it expands and becomes less dense– This causes pressure to fall
• Humid air is lighter than dry air– This is because water
molecules are lighter than the gasses they displace (replace) in the air
Measuring Air PressureMeasuring Air Pressure
• A barometer is an instrument used to measure air pressure.
• Meteorologists measure air pressure in millibars
• On a weather map, On a weather map, isobarsisobars connect places that have the connect places that have the same air pressuresame air pressure