1. The Atmosphere

3. The Atmosphere It is a thin layer of air surrounding the Earth
Contains gases essential to life
O2 – cellular respiration
CO2 – photosynthesis
Absorbs harmful solar radiation
Composition: (p.223)
78% Nitrogen
21% Oxygen
1% Other Gases

4. Layers of the Atmosphere p.225
Exosphere (500+ km)
Practically empty. Few air particles
Satellites and ISS (400 km)
Thermosphere ( km)
Auroras occur here
Space Shuttle
Space considered to start around 100 km
Mesosphere (50-80 km)
Coldest layer
Shooting stars: meteors burning up in the mesosphere
Stratosphere (15-50 km)
Contains ozone layer
Airplanes cruise at this height or just below (low air resistance and no weather)
Troposphere (0-15 km)
Weather occurs in this layer

6. Atmospheric Pressure The pressure of the air in the atmosphere
High pressure: more air molecules collide with an area
Low pressure: less air molecules collide with an area
Collisions (and thus pressure) increase when:
More air molecules are present
Temperature increases which increases air molecule speed

8. Atmospheric Circulation
Changes due to density changes and temperature
Warm air moves towards the poles where it is cooled, then cycles back to the equator
Warm air rises and cold air descends (due to density)

9. Global Scale Atmospheric Circulation
Sun warms the Earth unevenly. Warmest at equator and coldest at poles.
Temperature variation leads to different air pressure and makes dominant wind circulation patterns.

13. Coriolis Effect Rotation of the Earth deviates the winds Explanation:
Real Example:

14. Circulation Cells
Circulation of wind form loops called circulation cells

15. Prevailing Winds Major wind currents that exist on Earth
1- Polar easterlies: in polar regions, blow east to west
2- Trade winds: near equator, blow west to east
3- Westerlies: middle latitudes, blow west to east

16. Other Winds – Jet Streams
Subtropical jet stream
Around 30th parallel
400km/h at 11km above ground
Polar jet stream
Around 60th parallel
300km/h

17. Air Masses
Large expanse of air with relatively uniform temperature and humidity

18. Air Mass Characteristics
Humidity : humid or dry (maritime or continental)
Temperature: cold or warm (polar or tropical)
In Quebec, we are subjected to the warm tropical maritime air mass and cold polar air mass

19. Fronts

20. Fronts
When two air masses meet, a front occurs. (they do not mix). It is a boundary and a transition zone where wind direction, temperature, relative humidity change rapidly
Simulation:
Water demo:

21. Fronts Cold Front: a mass of cold air meeting a mass of warm air
The cold air rapidly pushes the warm air up, which condenses into rain clouds (heavy rain and rapid)

22. Fronts Warm Front: a mass of warm air meeting a mass of cold air
The warm air gradually pushes the cold air away. Clouds are lighter and more dispersed.

24. 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
To recap:
Anticyclone = cold front = high pressure = sun and clear skies
Depression = warm front = low pressure = rain and clouds

25. Anticyclone and Depressions
An anticyclone is caused by cold air falling to the ground, creating an area of high-pressure ground (symbol: H)
In a anticyclone, falling air molecules prevent cloud formation
A depression is caused by warm air rising up, creating an area of low-pressure on the ground (symbol: L)
In an depression, rising air molecules encourages cloud formation
Both will turn due to the Coriolis effect. The direction depends on the hemisphere.

26. Anticyclone and Depressions

27. Strong Depressions  Storms
More intense depressions that form over warm ocean waters can lead to storms (huge diameter and large wind speeds)
A cyclone is a tropical storm characterized by violent winds revolving around an area of low pressure
Cyclone = hurricane = typhoon; it only depends on where in the world the storm is formed
Flying through the eye video:

28. Hurricanes
A large cyclone (depressions) characterized by violent winds