Atmosphere • Layer of gases that surrounds the Earth • Held in place by Earth’s gravity
Layers of the atmosphere • Five major layers • Troposphere • Stratosphere • Mesosphere • Thermosphere • Exosphere
Atmosphere - composition • Nitrogen – 78.08% • Oxygen – 20.95% • Argon – 0.9% • Carbon dioxide – 0.03% • Trace amounts of various other gases • Water vapor can make up – 0 to 4% of the atmosphere, depends on location
Weather • The state of the atmosphere at a particular time and place • Includes • Pressure • Temperature • Humidity • Clouds • Precipitation • Wind • Visibility
Troposphere • Troposphere – atmosphere layer closest to Earth’s surface • Most of Earth’s weather occurs in this layer • Jet stream is a high altitude wind found at the upper level of the troposphere • Temperature of air in troposphere decreases as you go further away from Earth’s surface
Troposphere • Air in the troposphere is heated indirectly by the electromagnetic energy from the Sun • When the Sun’s energy is absorbed or reflected by the land and water on the surface of the Earth, it is converted to heat energy and transferred to the air directly above the land or water. • Air closest to Earth is the warmest
Temperature and Volume • When a gas is heated, it tends to expand • This tendencyis described ina law calledCharles’ Law Volume Temperature
Density • Amount of matter that is found in a particular volume • Compactness of matter • Density = mass ÷ volume • Units g/mL or g/m3
Density • When air is heated, the molecules have more energy, move faster, and spread out. • Mass does not change, but volume increases • When air is heated – density decreases
Unequal heating of Earth • Not all parts of the Earth are heated equally • Area at the equator receives more direct sunlight and is warmer than the poles
Unequal heating of Earth • Warm air at the equator rises and is less dense than cooler air at the poles • Cold air at the poles sinks and is more dense than warmer air at the equator
Air pressure and atmospheric motion Q: What makes the wind blow? A: Air pressure differences.
Is air rising or sinking at the equator?
Is air rising or sinking at 30°N?
Air pressure • Force exerted by molecules in atmosphere due to gravity and temperature
PGF: Pressure gradient force – winds blow from high pressure to low Where are winds the fastest?
Wind blows from areas of to areas of high pressure low pressure
In a high pressure area, air will (rise, sink) because the air is (less, more) dense. This is because the air is (cold, warm) and (rises, sinks). Therefore, clouds CANNOT form.
In a low pressure area, air will (rise, sink) because the air is (less, more) dense. This is because the air is (cold, warm) and (rises, sinks). Therefore, clouds are LIKELY to form.
Air Pressure Can you feel it?
Air Pressure • Air pressure is the measure of the force with which air molecules push on a surface. • Air Pressure is GREATEST at the surface of Earth because there is more of the atmosphere above you to push down on you.
Air Pressure is dependent on Density • Denser air will have a higherair pressure- there are more air molecules in a given space to push down on you • Less dense air will have a lowerair pressure- there are fewer air molecules to push down on you. More Dense= more particles to push down on you Less Dense= fewer particles to push down on you
Air Pressure is affected by 3 factors • 1- Elevation, or altitude • 2- Temperature • 3- Water content
Impact of Elevation on Air Pressure • As you move up through the atmosphere, air pressure decreases. • There are fewer air molecules above you to push down on you, so the force of the air will be less.
Impact of Water Content (humidity) on Air Pressure • Moist air is less dense than dry air, and therefore has a lower air pressure. • A water molecule has less mass than other molecules that make up the air. If you replace some of the air molecules with water molecules, the water lowers the density (and lowers the air pressure)
Impact of Temperature on Air Pressure • Warm air is less dense than cold air. Therefore, warm air has a lower air pressure and cold air has a higher air pressure. • The molecules in warm air are moving fast and are spread farther apart. Therefore there are fewer air molecules in a given area to push down on you. Warm Air Cold Air
Barometer • The piece of equipment used to measure air pressure is a Barometer • Air Pressure is measured in millibars (mb) on a barometer. Mercury Barometer Aneroid Barometer
Air Pressure Affects the Weather • Air pressure in a weather system reflects the amount of water in the air, which affects the weather. • Low air pressure usually results in Bad weather: stormy, cloudy, overcast. • High air pressure usually results in Goodweather: clear skies, no precipitation
Air Pressure on a Weather Map • Areas of High and Low pressure on shown on a weather map with an H or an L.
Front: boundary between air masses of two different densities Fronts
Warm front: an area where a warm air mass is replacing a cooler air mass Warm front
Cold front: an area where a cold air mass is replacing a warmer air mass Cold front
Animation of Fronts Animation of Fronts