The Atmosphere Ch 7 pg. 222-238

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

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

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***

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.

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

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)

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

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.

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

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

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.

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