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Air Exerts Pressure
Air molecules are constantly in motion, similar to a room full of
bouncy balls
 With every bounce, air is exerting a force
 You do not feel the pressure of air at any one time because it is
balanced on all times. When air pushes from behind it is
equally pushing in the front
Air Pressure is the force of molecules pushing on an area, air
in all directions
Air Pressure Related to Altitude and Density:
 Air pressure is determined by the weight (mass) of the air above it
 As you move up in the atmosphere you are also moving up in altitude, this
upward movement has less weight (mass) so there is less air pressure; less air
pressure, density and mass in Flagstaff.
If air pressure was the same in all places air would not move; air pressure is
always moving from areas of high pressure to areas of low pressure. Much like
opening a can of tennis balls or soda, there is little pressure inside, but the high
high pressure on the outside rushes inward.
Barometers are instruments that measure the amount of air pressure. It is a flexible machine
that expands and contracts with the change in pressure
Movement of Air
Uneven heating of Earth’s surface causes air to move
Weather is the condition of Earths Atmosphere at a particular time and place.
-
Wind is an important factor of weather
Wind is air that moves horizontally or parallel to the ground
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Much like air pressure, wind moves from areas of high pressure to low pressure
Formation of Wind:
1.
First, low pressure, or warm air, rises
2.
Second, high pressure, or cold air, sinks
3.
Winds then move across the surface of Earth
This can be such a slight change that you may not even feel the movement of the wind or air
Some winds die after a short distance.
Global winds, however, travel long distances and may last weeks. Uneven
heating between the poles and the equator cause the winds
Coriolis Effect Curves the winds from the poles as the Earth rotates
Global Wind Belts
Doldrums are low pressure sections of air that do not move air quickly and are found at the equator. Warm air is
rising. The rising air in this area produces clouds and heavy rains
Horse Latitudes are high pressure sections of air that do not move quickly and are above and below the equator. so
cold air is sinking. Weather tends to be clear and dry in this area but can bring rain across the United States
Wind Belts:
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Trade Winds blow from the east and move from the horse latitude to the equator
-
Westerlies blow from the west and move from the horse latitudes to the poles. Bring storms across the United
States
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Easterlies blow from the east and move from the poles to mid-latitudes. Stormy weather occurs when the
easterlies cold air meets the warm air of the westerlies
Travel and Wind:

The calm regions of the doldrums and horse latitudes make sailing difficult, boats may not move for days or
weeks, Wind belts are more ideal for sailing.
Jet Stream and Breezes
Jet Stream:
1.
Flow in the upper troposphere lower stratosphere
2.
Air moves at speeds greater then 200kilometers per hour
3.
Caused by uneven heating of Earths surface
4.
Two jet streams in each hemisphere; polar and subtropical
5.
Polar Jet streams affect weather in North America
6.
Jet Streams affect air travel because planes fly in this region. Depending on the strength of the wind your plane
plane ride may be shortened or lengthened
Local Breezes:

Winds change daily in a regular pattern

As beaches heat up during the day the warm air rises and flows out to sea. Because the water takes longer to
heat up the water sends cool air to shore. This is why you would feel cool breezes while on the beach

This same effect takes place in mountains and valleys. Mountains (beach) heat faster then valleys (sea).
Monsoons
Monsoons are winds that change directions with the
seasons
- Caused by different heating and cooling rates
- Flow long distances and effect large areas
- Winter Monsoons occur when land is colder then the
sea
- Summer Monsoons occur when land is much hotter
then sea
Temperature Affects Water in the Air
1. Water is always in the atmosphere
2. When temperatures change water changes form
3. Evaporation is changing from a liquid to a gas and condensation is a gas
changing into a liquid
4. Gas in this process is water vapor
5. Precipitation is any liquid that falls to Earths surface
Humidity is the amount of water in the air
- Saturation of the air means that the amount of water evaporating is equal
to the amount of water that is condensing
Formation of Clouds
Clouds form when water vapor condenses
- Warm air rises and cools as it gets higher, the cooling of the air
forms ices crystals or water droplets, these droplets form the
clouds
- The water must condense on to something hard, such as the
dust particles that are in the air. Smoke, and salt are other
examples
Fog: A cloud that rests on the ground or a body of water. Has a
appearance. Forms when the ground is colder then the air around it
Clouds
Cirrus:
A. Curl of Hair, form in high altitudes
B. Made of ice crystals, feathery appearance.
C. Winds form the tails of these clouds, these tails show the
direction of the wind in the upper troposphere. Seen in
fair weather, but can indicate that a storm is approaching
Clouds Continued
Cumulus:
• Heap or Pile often like cotton balls.
• Puffy white clouds, with dark bases.
• Form in the day time when warm air rises and the vapor condenses. If they keep
growing they produce showers.
• Smaller ones only produce light showers that last less then an hour, larger ones that
reach 18kilometers (11miles) will produce large thunderstorms
Stratus:
• Spread-out, flat layers, appear gray.
• Are smooth clouds because there is little wind when forming the clouds.
• If they are low they can produce light and steady precipitation as well as block the sun
sun and moon. When higher in the atmosphere they are thinner and produce a halo of
of light around the sun and moon.
In your Notebooks
 Create a diagram of the 4 types of clouds and the
weather they bring(cirrus, cumulus, stratus, fog)
 Create a diagram of the way wind is formed
 Create a diagram that shows the relationship
between air pressure and density
 Create a diagram of the Coriolis effect