1. Atmosphere

2. Atmosphere Layer of gases that surrounds the Earth
Held in place by Earth’s gravity

3. Five major layers Layers of the atmosphere Troposphere Stratosphere
Mesosphere
Thermosphere
Exosphere

4. 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

5. Weather The state of the atmosphere at a particular time and place
Includes
Pressure
Temperature
Humidity
Clouds
Precipitation
Wind
Visibility

6. 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

7. 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

8. Earth-Atmosphere Energy Balance Diagram

9. Temperature and Volume
When a gas is heated, it tends to expand
This tendency is described in a law called Charles’ Law
Volume
Temperature

10. Density Amount of matter that is found in a particular volume
Compactness of matter
Density = mass ÷ volume
Units g/mL or g/m3

11. 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

12. 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

13. 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

14. Air pressure and atmospheric motion
Q: What makes the wind blow?
A: Air pressure differences.

15. Global air circulation patterns

17. Is air rising or sinking
at the equator?

18. Is air rising or sinking
at 30°N?

19. Air pressure
Force exerted by molecules in atmosphere due to gravity and temperature
July 11, 2006
NY Times
As the World Wobbles
Late last November, as a big low-pressure system built over Europe and Asia and high pressure settled in over the Pacific and Atlantic Oceans, the shifts in the atmosphere caused the earth to jiggle ever so slightly, like a hiker adjusting to a shifting load in a backpack.
As a result, the North Pole and its southern counterpart moved about four inches by one measure. (There are several ways to define the poles.)
Despite its diaphanous appearance, the atmosphere weighs about 5,000 trillion metric tons, and its mass is unevenly distributed. All those ridges and troughs on a weather map reflect differences of billions of tons of gases.
Scientists have long known that as the atmosphere shifts, it influences the earth’s rotation. The recent advent of satellites’ global positioning systems made it possible to confirm even the tiniest movements.
There were well-known, regularly occurring wobbles in the earth’s rotation that could shift the poles 30 feet over a year or more. These shifts blocked the detection of subtler, quicker movements caused by day-to-day changes in the atmosphere and the oceans.
Now, these small shifts are being measured by institutions devoted to tracking the planet’s behavior, including the earth orientation department of the United States Naval Observatory and the “time, earth rotation and space geodesy section” of the Royal Observatory of Belgium.
Experts at the Belgian observatory and the Paris Observatory found the November polar shift and a series of other little loops by looking particularly closely at a period from last November through February, when two of the larger regular wobbles in the axis canceled each other out.
They reported their analysis in the July 1 issue of Geophysical Research Letters.

20. PGF: Pressure gradient force – winds blow from high pressure to low
Where are winds the fastest?

21. Which pressure gradient would result in greater wind velocity?

22. Wind blows from areas of
to areas of
high
pressure
low
pressure

23. Air Pressure and density

24. This is because the air is Therefore, clouds CANNOT form.
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.

25. This is because the air is
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.

26. Air Pressure
Can you feel it?

27. 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.

28. As you move UP through the atmosphere, air pressure decreases.

29. Air Pressure is dependent on Density
Denser air will have a higher air pressure- there are more air molecules in a given space to push down on you
Less dense air will have a lower air 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

30. Air Pressure is affected by 3 factors
1- Elevation, or altitude
2- Temperature
3- Water content

31. 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.

32. 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)

33. 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

34. 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

35. Mercury (or Water) Barometer

36. 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 Good weather: clear skies, no precipitation

37. Air Pressure on a Weather Map
Areas of High and Low pressure on shown on a weather map with an H or an L.

38. High Pressure

39. Low Pressure

40. Low vs. High

41. Fronts
Front: boundary between air masses of two different densities

42. Warm front
Warm front: an area where a warm air mass is replacing a cooler air mass

44. Cold front
Cold front: an area where a cold air mass is replacing a warmer air mass

46. Animation of Fronts
Animation of Fronts

47. molecules move fast or slow molecules are packed together or far apart
low pressure
high pressure
warm or cold air
warm
cold
air rising or sinking
rising
sinking
clouds or no clouds
clouds
no clouds
molecules move fast or slow
fast
slow
molecules are packed together or far apart
far apart, less dense
packed together, dense
moist or dry
moist
dry