Winds What is Wind The horizontal movement of

Winds

What is Wind? The horizontal movement of air from High pressure to Low pressure. • H L Air moving up or down (vertical) is called a current

L= Low

Pressure is caused by the characteristics of the air Warmer Air X X X Molecules move faster and are farther apart. Less Dense Cooler Air More Dense X X X X X X X X Molecules are close together and move slowly.

Warm Air Rises Cool Air Sinks Warm Air Rising Cool Air Sinking

Convection Currents Cool Air Sinking Warm Air Rising

High Pressure Ok, High Pressure is 1. Dense (heavy) 2. Cool 3. Creates Clear Skies AHHHH! High Pressure

Low Pressure Ok, Low Pressure is 1. Less Dense (heavy) 2. Warmer 3. Brings Lousy Weather L Whew! Low Pressure

High Pressure Low Pressure = = Happy Weather Lousy Weather HL

Winds Blow from HIGH to LOW

low pressure warm or cold air rising or sinking clouds or no clouds clockwise or counterclockwise wind direction winds toward or away from the center high pressure

In a high pressure area, air will (rise, sink) because the air is (less, more) dense. This is because the air is (cold, warm) and (rises, sinks). Therefore, clouds CANNOT form.

In a low pressure area, air will (rise, sink) because the air is (less, more) dense. This is because the air is (cold, warm) and (rises, sinks). Therefore, clouds are LIKELY to form.

There Are Two Kinds of Winds: Global and Local • Global Winds are Winds that blow over long distances around the Earth. • Local Winds are winds that blow a short distance.

Global Winds

Why Do Different Parts of the Earth Have Different Temperatures? North Pole Equator South Pole Thus, radiation is more intense near the equator compared to the poles. For this reason, it’s warmer near the equator than at the poles.

Global Thermal Temperatures

Air Rises at the Equator • Air at the Equator is warm. • Warm air rises. • The Equator is a Low Pressure area.

What Happens to Rising Air at the Equator? • At the Equator, air rises; • As the air moves upward, it cools, • The air begins to turn to move downward. • Cold air sinks at the 30 o zone.

Winds blow from High Pressure to Low Pressure

Let’s Label High Pressure 90°N Low Pressure 60 °N High Pressure 30°N Low Pressure 0° High Pressure 30°S Low Pressure 60°S High Pressure 90°S

Names of Winds • IMPORTANT: Winds are named from the direction they come. • North winds comes from the north; south winds come from the south. • Southeast winds come from the southeast and blow northwest; • Northeast winds come from the northeast and blow to the southwest.

Let’s Label Easterlies Polar Easterlies Trade Winds Polar Easterlies

Trade Winds • The TRADE WINDS are the winds blowing towards the equator. • These winds are Easterlies, blowing from the east. – South of the equator, the winds blow from the southeast – North of the equator, the winds blow from the northeast. • They were named because traders from Europe sailed in these zones on their way to the new world.

Let’s Label Westerlies Prevailing Westerlies

North is Located in the Westerly Wind Belt

Why Don’t The Winds Blow in Straight Lines? • Cold air from both the South Pole and North Pole blows towards the 60 o zone • But the air doesn’t flow in a straight line

Coriolis Effect • Since the earth rotates, winds do not blow directly from north to south or south to north. • Winds curve • They curve because the earth rotates or spins on its axis. • The Coriolis Effect is the curving of winds due to the earth’s rotation.

The ball is going straight, but it looks like it is curving.

Global Wind Animation http: //www. geo. hunter. cuny. edu/ ~tbw/wc. notes/7. circ. atm/animati ons/Global. Wind. html

Zones of NO WIND Doldrums At the equator, which is 0 o latitude, there is a windless zone called the Doldrums. Horse Latitudes At 30 o N and 30 o S, there is a windless zone called the Horse Latitudes.

Horse Latitudes And The Doldrums

Doldrums • Since the Trade Winds blow from both the North and South, a calm zone occurs. • This zone is called the “DOLDRUMS. ” • In this zone, there are no winds. Ships often got stalled for long periods because they needed wind to blow their sails.

Horse Latitudes The Horse Latitudes are zones of calm winds at the 30 o Latitude Lines. The term horse latitudes originates from the days when Spanish sailing vessels transported horses to the West Indies. Since there was no wind, the sail ships that entered this zone, would get stuck for weeks. Since water and food shortages occurred, the crews found it necessary to throw their horses overboard.

o 30 North and South Latitude This is an area of high pressure. Sinking air means no clouds or rain. Air from the Equator and from the 60 o Latitudes cool and Along this latitude, (between descend at the 30 o Latitude. 15 o to 35 o) many of the major deserts are found

Local Winds • Winds that blow short distances and in any direction (depending on pressure) • Remember, winds always blow from areas of high pressure to low pressure.

Sea Breeze any wind that blows from a large body of water toward or onto a landmass Land Breeze is the reverse effect: dry land also cools more quickly than water and, after sunset a sea breeze dissipates and the wind instead flows from the land towards the sea