The Atmosphere

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

Layers of the Atmosphere p.225 Exosphere (500+ km) Practically empty. Few air particles Satellites and ISS (400 km) Thermosphere (80-500 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

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

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)

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.

Coriolis Effect Rotation of the Earth deviates the winds Explanation: https://www.youtube.com/watch?v=mcPs_OdQOYU Real Example: https://www.youtube.com/watch?v=dt_XJp77-mk

Circulation Cells Circulation of wind form loops called circulation cells

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

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

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

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

Fronts

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: https://www.youtube.com/watch?v=huKYKykjcm0 Water demo: https://www.youtube.com/watch?v=naarbGHoAGU

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)

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.

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

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.

Anticyclone and Depressions

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: https://www.youtube.com/watch?v=a-SnxC-BkPo

Hurricanes A large cyclone (depressions) characterized by violent winds