1. The Atmosphere
Ch 7 pg

2. Atmosphere Def: The layer of air surrounding the Earth
Composition of Air: Nitrogen (78%), Oxygen (21%), other trace substances
Function:
Act as a barrier and protect us from the dangerous UV rays
Ensure a relatively stable climate
Ensure the presence of O2 for cellular respiration and CO2 for photosynthesis
The atmosphere covers our planet because of our gravitational field
Atmospheric Circulation: The movement of the air in the atmosphere on a global scale around the Earth

3. Atmospheric Circulation (AC)
Occurs due to changes in density and temperature
Warm air moves towards the poles
The air then cools and returns towards the equator
Warm air RISES and cool air DESCENDS

4. Atmospheric pressure Def: The pressure of the air in the atmosphere
Air is a fluid so travels from areas of high pressure (cold) to areas of low pressure (hot)
The movement of air molecules:
Increase in air molecules = increase in atmospheric pressure
Decrease in air molecules = decrease in atmospheric pressure
***Warm air is therefore less dense than cold air***

5. Global scale atmospheric circulation
The sun warms the earth unevenly (warmer at the equator and colder at the poles). The temperature variation will bring a difference in pressure and will make the warm air rise. This is known as convection.

6. Coriolis effect
Rotation of earth causes wind to deviate from destination
Winds deviating to the right in the Northern Hemisphere
Winds deviating to the left in the Southern Hemisphere

8. Circulation cells Winds form loops called circulation cells
Hadley Cells
Ferrell Cells
Polar Cells
Warm air rises at the equator and moves to the 30th parallel
Warm air rises from the 30th parallel and moves towards the 60th parallel
Warm air rises from the 60th parallel and moves towards the poles
Collides with winds from Ferrell cells and moves back to the equator
Collides with the winds from polar cells and moves back to the 30th parallel
Air cools at the poles and moves back to 60th parallel
Creates the trade wind
Creates the Westerlies (from west to east)
Creates the polar easterlies (from east to west)

9. Prevailing Winds Other Winds
Major wind currents that blow in a particular direction.
1- Polar easterlies: in polar regions and blow from east to west
2- Trade winds: near equator blow from west to east
3- Westerlies- in middle latitudes blow from west to east
Other Winds
Jet streams
1- Subtropical Jet Stream
Around the 30th parallel
Travels at 400 km/h 11 km above the surface
2- Polar Jet Stream
Around the 60th parallel
Travels at 300 km/h

10. Air Masses
Large expanse of air with relatively uniform temperature and humidity.
Characteristics:
Humidity (humid or dry)
Temperature (cold or warm)
Fronts: A boundary separating 2 different masses of air and causes weather The 2 fronts do not mix; they cause weather patterns.

11. Types of Fronts Cold: Anticyclone Warm: Depression
Cold air meets warm air
Warm air meets cold air
High Pressure System
Low pressure system
Descending cold air prevents cloud formation
Rising warm air creates cloud formation, humidity and rain
In winter: clear skies, sunny and very cold
In summer: clear skies and sunny
In winter: warmer weather and snow
In summer: hot, humid, cloudy with rain

13. Change from a warm front to a cold front = Thunderstorms, lightning and heavy rain
Change from a cold front to a warm front = Clouds and rain
Hurricanes: A large cyclone (depression) characterized by violent winds

15. Past Exam Question
1. An air mass that originated in the Caribbean now lies over Québec, while a fast-moving air mass from the far north is heading down toward the southern part of the province. Explain what happens when these two air masses meet. In your explanation, discuss the various phenomena involved.

16. Past Exam Question
2. A warm air mass meets a cold air mass. What kind of weather occurs when these two air masses meet?
A) Light showers C) A hurricane
B) Heavy thunderstorm D) A sunny day