unit 2: climate winds and climate. the circulation of air follows a general pattern: ◦ the...
TRANSCRIPT
World GeographyUnit 2: Climate
Winds and Climate
The Circulation of Air The circulation of air follows a general
pattern:◦The equator receives the most solar energy,
therefore is heated the most.◦Air above the equator heats rapidly and
expands, becoming less dense.◦This air rises◦As the air rises, it cools and is pushed towards
the poles, it is pushed by air still rising from the equator.
◦This cooling air becomes more dense, and begins to fall back to earth.
◦As it falls back to earth it forces colder air toward the equator where the cycle continues.
The Circulation of Air This process is known as a convection cell Convection Cell: A current in the atmosphere
in which warmer, lighter air moves upward and is replaced by colder, heavier air.
The movement of the air depends on the density of the air◦ Warm air is moist, less dense, and lighter.
These are low pressure areas.◦ Cool air is dry, dense, and heavy.
These are high pressure areas When areas of low and high pressure are next
to each other the air flows from high to low. This flow is known as Wind.
The Circulation of Air Air moves vertically in convection cells to
equalize temperature. Air moves horizontally by wind to equalize
pressure.
Prevailing Wind: The most frequently occurring wind direction at a given location.
The circulation of air from the equator to the poles and back is complicated by two things:1. The spinning of the planet2. The uneven distribution of water and land on the
planet
Prevailing Wind
The movement of air from the equator to the poles is broken into three convection cells in each hemisphere:◦ Trade winds: 0⁰-23.5 ⁰ (equator to tropics)◦ Westerlies : 23.5 ⁰ - 66.5 ⁰(tropics to arctic circle)◦ Polar easterlies: 66.5 ⁰-to pole (arctic circle to
pole) These latitudes do change due to two
factors:1. Variations in Earths Surface: Ocean and
Continent2. Earth’s relative position to the sun: They will
move with the seasons
Prevailing Winds
Prevailing Winds
The apparent deflection of moving objects (wind, ocean currents, missiles) from traveling in a straight path, in proportion to the speed of Earth’s rotation at different latitudes.
Deflection is:◦ To the right in the Northern Hemisphere◦ To the left in the Southern Hemisphere.◦ Maximum effect at the poles◦ Minimum effect at the equator◦ http://www.youtube.com/watch?v=i2mec3vgeaI
Coriolis Effect
Coriolis Effect and Wind Direction
Wind systems are driven by pressure belts that can be found in the different areas of prevailing wind.
These are areas of high and low pressure. High pressure:
◦ Downward moving◦ Pushing outward-◦ Spins clockwise in the north and counter
clockwise in the south Low pressure:
◦ Rising air◦ Air that pulls inward◦ Spins counter clockwise in the north and
clockwise in the south
The Major Pressure Belts
High Pressure and Low Pressure
The Pressure systems are◦ Equatorial Low Pressure Trough◦ Subtropical High-Pressure◦ Sub Polar Low Pressure◦ Polar High
Pressure Belts
Equatorial Low Pressure Trough:◦ Broken band of clouds that straddle the equator◦ Constant high sun altitude and consistent day
length make enormous amounts of energy available Lots of light, wet, ascending air.
◦ As air rises it cools, and water in the air condenses.◦ Home of the intertropical convergence zone, ◦ Shifts between the tropics depending on season.
◦This area is dominated by the TRADE WINDS!!!
Pressure Belts
Subtropical High- Pressure Cells: ◦ Hot, dry, desert air◦ Cloudless skies◦ Air forced downward by compression from low
pressure cells, is heated.
◦THIS AREA IS ASSOCIATED WITH THE WESTERLIES
Pressure Belts
Subpolar Low-Pressure Cells:◦ Cool, moist air.◦ These cells DOMINATE in the winter, weakening,
or disappearing in the summer.
◦THESE CELLS FORM BETWEEN THE WESTERLIES AND POLAR EASTERLIES
Pressure Belts
Polar High-Pressure Cells:◦ Frigid, dry deserts◦ These are weak systems.◦ Near the poles there is little energy from the
sun to power up weather systems
◦THIS PRESSURE BELT IS RESPONSIBLE FOR FORMING THE POLAR EASTERLIES
Pressure Belts
Land-Sea breezes occur on most coastlines. However they have different characteristics.
Land and Sea Breezes
During the day the land is heated by the sun.
This causes air to warm and rise forming a low pressure system over the land.
As the air rises it is pushed over the sea where it cools and descends (high pressure)
This high pressure is drawn into the land creating a breeze that comes off of the water.
Sea Breeze
Sea Breeze
At night water is often warmer than land This causes the air above the water to rise,
forming a low over the water. As the air rises it is driven in over the land,
cools and descends. The cool air is drawn back out to sea by the
low pressure. This creates a breeze that comes from the
land.
Land Breeze
As seasons change the temperature difference will cause pressure belts and prevailing winds to shift.
The equatorial low follows the sun between the tropics with the seasons.
This causes the other systems to shift to compensate.
Wind Systems and Temperature
WARM AIR RISES FORMING LOW PRESSURE
AS AIR RISES IT COOLS
COOL AIR DESCENDS FORMING HIGH PRESSURE
COOL AIR CANNOT HOLD MOISTURE AS WELL
CONDENSATION HAPPENS WHEN AIR CANNOT HOLD ITS MOISTURE
Points to Remember:
Orographic Precipitation: (relief rainfall) this forms when moisture-laden air masses are forced to rise over high ground. The air is cooled, the water vapour condenses, and precipitation occurs◦ Windward side: The side of the mountain that
the prevailing wind blows against. Where the air rises, and precipitation occurs
◦ Leeward side: The side of the mountain in which the air begins to descend again. This area is dry as the air mass has lost its moisture.
◦ Rainshadow: Area where little rain falls due to the loss of moisture within the air mass due to its rising over a landform.
Precipitation: Orographic
Frontal Precipitation: Rain resulting from where two air masses meet.
As air is forced to rise over a low pressure system it cools, and drops its moisture.
Precipitation: Frontal
Convection rainfall happens when the land is heated by the sun. The air above this land is then heated and rises. Moisture from the Earth’s surface evaporates and rises with the warm air. As the air rises it cools so this moisture condenses and falls as rain. The continuous cycle of rising warm air and falling cool air creates a convection current in the atmosphere.
This type of rainfall is generally not accompanied by wind.
Precipitation: Convectional
Where does each type of rainfall occur? Orographic: Where westerly winds meet
coastal mountains after crossing bodies of water.
Frontal: where low pressure meets high pressure.
Convectional: Mostly over the tropics, however sometimes in the summer.
The Relationship Between Precipitation and Location