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The Atmosphere
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The Atmosphere
It is a thin layer of air
surrounding the Earth
Contains gases essential to life
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O2 – cellular respiration
CO2 – photosynthesis
Absorbs harmful solar
radiation
Composition: (p.223)
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78% Nitrogen
21% Oxygen
1% Other Gases
Layers of the Atmosphere p.225
Exosphere (500+ km)
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Practically empty. Few air particles
Satellites and ISS (400 km)
Thermosphere (80-500 km)
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Auroras occur here
Space Shuttle
Space considered to start around 100 km
Mesosphere (50-80 km)
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Coldest layer
Shooting stars: meteors burning up in the mesosphere
Stratosphere (15-50 km)
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Contains ozone layer
Airplanes cruise at this height or just below (low air
resistance and no weather)
Troposphere (0-15 km)
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Weather occurs in this layer
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Atmospheric Pressure
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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
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Collisions (and thus pressure) increase when:
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More air molecules are present
Temperature increases which increases air molecule speed
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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)
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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.
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Coriolis Effect
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Rotation of the Earth deviates the winds
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Explanation:
https://www.youtube.com/watch?v=mcPs_OdQOYU
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Real Example:
https://www.youtube.com/watch?v=dt_XJp77-mk
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Circulation Cells
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Circulation of wind form loops called circulation cells
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Prevailing Winds
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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
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Other Winds – Jet Streams
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Subtropical jet stream
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Around 30th parallel
400km/h at 11km above ground
Polar jet stream
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Around 60th parallel
300km/h
Air Masses
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Large expanse of air with relatively uniform temperature
and humidity
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Air Mass Characteristics
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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
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Fronts
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Fronts
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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
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Simulation:
https://www.youtube.com/watch?v=huKYKykjcm0
Water demo:
https://www.youtube.com/watch?v=naarbGHoAGU
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Fronts
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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)
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Fronts
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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.
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Change from a warm front to a cold front =
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Change from a cold front to a warm front =
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Thunderstorms, lightning and heavy rain
Clouds and rain
To recap:
Anticyclone = cold front = high pressure = sun and clear
skies
Depression = warm front = low pressure = rain
and clouds
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Anticyclone and Depressions
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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.
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Anticyclone and Depressions
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Strong Depressions  Storms
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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
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Hurricanes
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A large cyclone (depressions) characterized by violent
winds
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