Surface and Local Winds

7/31/2019 Surface and Local Winds

1/12

5/28/12

GLOBAL AND LOCALWINDSWHAT CAUSES WIND?

When the sun warms the surface ofEarth, the surface heats the air above it.

As a result, the air becomes less dense,which forms an area of low pressure.Areas where cold air sinks toward thesurface are areas of high pressure. Asthe cold air moves, it pushes the warm,less dense air out of the way. Thismovement of air is called wind.


2/12

5/28/12

GLOBAL AND LOCALWINDS

Wind is air in motion relative to theearth's surface. Its principalcharacteristics are its direction, speed,and turbulence.

Wind direction and speed are usuallymeasured and expressed quantitatively,while in field practice turbulence is

ordinarily expressed in qualitative orrelative terms.

Surface wind speeds are measured withanemometers. The standard height at

which wind speed is measured is 20


3/12

5/28/12

Global Circulation (TheCoriolis Effect)

At the equator, Earths surface receives a lot ofdirect sunlight that heats the ground and the air. Asa result, air pressure is low at the equator. Thepoles, however, receive much less direct sunlight.

Therefore, the ground and air are not as warm, andair pressure at the poles is high. These pressuredifferences cause air to circulate from the polestoward the equator.

However, winds do not travel directly north orsouth, because Earth is rotating. The apparentcurving of the path of winds and ocean currentsdue to Earths rotation is called the Corioliseffect. Because of the Coriolis effect in the

Northern Hemisphere, winds traveling north curveto the east and winds travelin south curve to the


4/12

5/28/12

Zones of GlobalCirculationInter-tropical convergence zone (ITCZ)

This is where the N/E & S/E winds converge. Theseconverging winds are also called Trade Winds,because they were important to sailing ships.

Subtropical high-pressure zones

These are areas of dry, bright sunshine, and littleprecipitation. They cause deserts. It is an area ofwarm dry air found about 30 degrees N & Slatitudes.

Polar high-pressure zones

The intense cold causes dense air because

coldness causes contraction, and so there is littlemolecular space, therefore air cant lift. This


5/12

5/28/12


6/12

5/28/12

GLOBAL WINDS

Convection cells, pressure belts, andwinds combine with the Coriolis effectto produce air-circulation patterns

called global winds. Figure shows the major global wind

systems: polar easterlies, westerlies,and trade winds. Winds such as

easterlies and westerlies are named forthe direction from which they blow.

Global winds distribute heat around

Earths surface and affect ocean


7/12

5/28/12


8/12

5/28/12

LOCAL WINDS

Local winds generally move short distances andcan blow from any direction.

Like global winds, most local winds result fromdifferences in pressure that are caused by the

uneven heating of Earths surface.

However, these pressure differences result from adifferent process. The pressure differences thatcause local winds are caused by the properties of

the matter that makes up Earths surface. Forexample, some materials, such as rock, heat upmore rapidly than other materials. Areas of lowpressure form over material that heats up quickly.


9/12

5/28/12

LOCAL WINDS

Local winds often vary considerably inboth

speed and direction over short

intervals of time. They tend to blow ina series of gusts and lulls with thedirection fluctuating rapidly. Thisirregular air motion is known as

turbulence, which may be thermal ormechanical. nature. At the surface,turbulence is commonly identified interms of eddies, whirls, and gusts.


10/12

5/28/12

Sea Breezes and LandBreezes During the day, the land heats upfaster than the water does. The airabove the land becomes warmer

than the air above the water. Thewarm air above the land rises, andthe cold ocean air flows in to

replace it. At night, the land coolsfaster than water does. The coldair above the land flows towardthe ocean. So, the wind blowstoward the ocean at night .


11/12

5/28/12

a ey reezes anMountain Breezes

During the day, the air along themountain slopes heats up rapidly.This warm air rises up the

mountain slopes, creating a valleybreeze.

At night, the air along themountain slopes cools. This cool

air moves down the slopes into thevalley, producing a mountainbreeze.


12/12

5/28/12

Surface and Local Winds

Documents

Transcript of Surface and Local Winds