22 3 Atmospheric Circulation WIND The atmosphere is

22. 3 Atmospheric Circulation

WIND • The atmosphere is a mixture of gases • Wind is the movement of these gases • Named for the direction they come from • Gases move from areas of higher pressure to areas of lower pressure H L

Pressure Centers and Winds u Low pressure centers are also called Cyclones (counterclockwise*) u High pressure centers are also called Anticyclones (clockwise*) *Rotation direction in Northern Hemisphere

Pressure Differences • LOW Pressure • • • causes air to rise & generally takes water vapor up= Clouds and storms HIGH Pressure causes air to sink & generally keeps moisture out of the atmosphere= Winds ALWAYS move from HIGH pressure areas to Clear skies & nice LOW pressure areas!!!!!!! weather

CONVECTION Air is warmed at the surface Warm air rises Air is cooler higher in the troposphere Cold air sinks

Local Winds u Local winds are caused either by utopographic effects (mountains and land) OR uvariations in surface composition (near water)

Land & Sea Breezes Coastal Areas ØDuring the day, land heats up quicker than the water ØThe heated air above the land expands and rises=LOW pressure ØColder air over the water is denser= HIGH pressure ØPushes into land= SEA BREEZE

Land & Sea Breezes Coastal Areas • Land cools faster than • • • water The air above the water is warmer = LOW pressure Air above the land is cooler= HIGH pressure. Making a… LAND BREEZE

Land or Sea Breeze?

http: //www. classzone. com/books/earth_science/terc/content/visualizations/es 1903 page 01. cfm? chapter_no=visualization

Mountain & Valley Breezes Valley Breeze ØDuring the day, the valley floor heats up and air above it does too ØWarm air rises up the mountain ØAir cools as it goes up in elevation & clouds may form

Mountain & Valley Breezes Mountain Breeze ØAfter sunset the pattern reverses ØAs slopes cool, nearby air cools and sinks down the mountain.

Mountain & Valley Breezes

Global Winds!

Global Winds u Unequal heating and cooling of the atmosphere from continents and oceans creates high and low air pressures u Add in the rotation of the Earth and global wind patterns emerge

Non-Rotating Earth Model • On a hypothetical non-rotating planet with a smooth surface of either all land or all water, two large thermally produced cells would form.

Circulation on a Non-Rotating Earth Air would warm and rise at the equator and cool and sink at the poles.

Coriolis Effect • Click on image to watch video

The Coriolis Effect describes the apparent deflection of an object based on the rotation of the Earth below it.

The Coriolis Effect Objects appear to deflect to the right in the northern hemisphere and to the left in the southern hemisphere http: //nsidc. org/cryosphere/arctic-meteorology/images/coriolis. gif

Rotating Earth Model • When the effect of rotation is added to the global circulation model, the two-cell convection system breaks down into many smaller cells. http: //sparce. evac. ou. edu/q_and_a/images/bc 07. gif

Rotating Earth Model • These cells lead to the formation of the global wind belts.

Circulation on a Rotating Earth

Wind Belts

WIND BELTS § Trade winds are § § two belts of winds that blow almost constantly from easterly directions From 0 o to 30 o latititude Warm, moist, rising air (low pressure)

WIND BELTS § Westerlies are the prevailing winds that blow west-to-east in the middle latitudes § From 30 o to 60 o latititude

Wind Direction • The PREVAILING WIND is the wind that blows more often from one direction than from any other. • In the United States, the WESTERLIES consistently move weather from west to east across the continent.

WIND BELTS § Polar easterlies § § winds that blow from the polar high toward the subpolar low. From 60 o to 90 o latitudes. Cold and dry air masses

WIND-LESS BELTS § Doldrums converging trade winds at the equator (O latitude) creating calm areas § Horse latitudes diverging westerlies and trade winds (easterlies) create calm at approximately 30 latitude

The Jet Stream • Jet streams form at boundaries between convection cells; • High speed winds • Blow in upper troposphere and lower stratosphere

Identify the Wind Belts Click on the link below to see the wind belts in action and answer so questions! http: //meted. ucar. edu/hurrican/strike/orig/htc 5_1. htm

Global Winds Influenced by Continents • The only truly continuous pressure belt is the subpolar low in the Southern Hemisphere. • In the Northern Hemisphere, where land masses break up the ocean surface, large seasonal temperature differences disrupt the pressure pattern.

Energy from Wind