Air Exerts Pressure

1. 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 pressure moves in all directions

2. 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 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

3. 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 • Much like air pressure, wind moves from areas of high pressure to low pressure Formation of Wind: • First, low pressure, or warm air, rises • Second, high pressure, or cold air, sinks • 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.

4. 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

5. 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: • Trade Winds blow from the east and move from the horse latitude to the equator • Westerliesblow from the west and move from the horse latitudes to the poles. Bring storms across the United States • 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.

6. Jet Stream and Breezes Jet Stream: • Flow in the upper troposphere lower stratosphere • Air moves at speeds greater then 200kilometers per hour • Caused by uneven heating of Earths surface • Two jet streams in each hemisphere; polar and subtropical • Polar Jet streams affect weather in North America • Jet Streams affect air travel because planes fly in this region. Depending on the strength of the wind your 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).

7. 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

8. Temperature Affects Water in the Air • Water is always in the atmosphere • When temperatures change water changes form • Evaporation is changing from a liquid to a gas and condensation is a gas changing into a liquid • Gas in this process is water vapor • 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

9. 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 smooth appearance. Forms when the ground is colder then the air around it

10. Clouds Cirrus: • Curl of Hair, form in high altitudes • Made of ice crystals, feathery appearance. • 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

11. 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 and moon. When higher in the atmosphere they are thinner and produce a halo of light around the sun and moon.

12. 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