WINDSWINDS

Understand the Understand the cause of windcause of wind and and how it affects climatehow it affects climate

Chapter 4Chapter 4

Pages 59-67Pages 59-67

What is Wind?

A wind is a horizontal movement of air across a surface.

Vertical movements are currents or updrafts and downdrafts

Caused by what????

Heat versus cold!! Relate it to convection cells previously studied!!!

What causes wind? Unequal heating!

Unequal heating causes pressure differences .

Cold, heavy air sinks = high pressure

Warm, expanding air rises = low pressure

Winds blow from high (cold) to low (warm)

Anyone got a light????

Know that air blows from areas of high pressure to areas of low pressure.

The statement is fact.The statement is fact. Real examples:Real examples:

1.1. Air inside a balloonAir inside a balloon

2.2. ExhalingExhaling

3.3. Air powered pellet gunAir powered pellet gun

It is simply fact. It is simply fact. High and low pressures in the earth’s atmosphere High and low pressures in the earth’s atmosphere

are responsible for windare responsible for wind P. 59-61P. 59-61

Application - Land BreezeUsing your knowledge of wind predict & explain the wind direction below. P. 61

•FACT: Water holds heat longer than the land.

•At night, sea air is warmer than air over the land.

•Air rises over sea

•Relative Low pressure over sea

•Cold land air moves to lower pressure

Low Pressure

Land Breeze

Night time

Cool breeze

Off the land

Application - Sea Breeze► Using your knowledge of wind predict & explain the

wind direction below. P. 61

•FACT: Land heats up faster than the water

•During the day, air over the land is warmer than air over the sea

•Air rises over land

•Relative Low pressure over land

•Sea air moves to lower pressure

•Cold “Breeze” off the ocean during the day

Low Pressure

Sea Breeze

Day time

Cool Breeze

Off the ocean

Define the terms wind & prevailing Define the terms wind & prevailing wind. p.61-63wind. p.61-63Wind: is a horizontal movement of air across a surface. It results from air masses of different temperatures and

humidity lying next to each other. The resulting pressure variation causes “wind” to blow

from high pressure areas to low pressure areas.

Prevailing Wind: Is regular, predictable, normal wind direction for a

given area or region. Caused by global convection cells. Named after the direction from which it comes

Prevailing Winds Lab

Winds

Preva

iling

Describe how the coriolis force Describe how the coriolis force affects wind affects wind direction.direction.

Coriolis force = objects in motion tend to deflect to the right in north hemisphere to the left in south hemisphere Due to the earth’s rotation

Consequently winds: in the northern hemisphere tend to curve to the

right of their path. while in the southern hemisphere they deflect left

of their path.

Summary of prevailing windSummary of prevailing wind

Global highs and lows are due to uneven heating of the earth

Air moves from high pressure to low pressure creating winds

Winds are deflected in the directions indicated on the diagram due to the coriolis effect.

Make inferences about how winds are related Make inferences about how winds are related to major pressure belts. p.63to major pressure belts. p.63

Air rises at the equator It settles at the poles Result = 6 convection cells 3 above and 3 below the

equator.

Low pressures result where hot air rises.

High pressures result where air settles

Describe Orographic (Relief) rainfall p. 66

A relatively warm, moist air blows off the sea It is forced up by mountains (high relief) and cools at higher altitude As it cools, water vapor condenses into tiny water droplets forming

CLOUDS. Water droplets continue to grow in size & weight, they will no longer be

suspended and will fall as rain (or possibly snow!) Cool air holds less moisture Most rain falls on the windward side of the relief Leeward side is often in a dry rain shadow because the moisture has

all been lost

Chinook

Windward

Leeward

DefinitionsDefinitions Windward

• The side of the mountain receiving the wind• (consequently more precipitation as well)

Leeward• The side of the mountain sheltered from the

wind• (consequently receives less precipitation)

Rain Shadow• The area located on the leeward side of a

mountain that receives low amounts of precipitation.

• Mainly due to the air that descends on the leeward side has “dumped” on the windward side.

Describe Frontal rainfall p. 66

Warm Moisture laden air meets cold air Warm air is less dense & is forced up over the cooler, more dense

air As it cools, water vapor condenses into tiny water droplets

forming CLOUDS. Water droplets continue to grow in size & weight, they will no

longer be suspended and will fall as rain (or possibly snow!) Cool air holds less moisture

•Weather Front-2 fronts meet

•Hence the name frontal rain

Warm, moist air

FRONT

Describe Convectional rainfall p. 67Describe Convectional rainfall p. 67

Usually occurs in hot areas like tropics or continental summer Sun heats the earth causing large amounts of water to evaporate Hot air rises forming convection currents (hence the name) As it cools, water vapor condenses into tiny water droplets forming

CLOUDS. Water droplets continue to grow in size & weight, they will no longer be

suspended and will fall as rain (or possibly snow!) Cool air holds less moisture

•Often associated with thunder storms.

Air heated from the earth

Analyze the relationship between wind Analyze the relationship between wind systems and temperature. systems and temperature.

How do the How do the prevailing prevailing windswinds affect affect temperaturetemperature in: in:

ColumbiaColumbia Baffin IslandBaffin Island NewfoundlandNewfoundland

A - ColumbiaColumbia

B -Baffin IslandBaffin Island

C - NewfoundlandNewfoundland

Analyze the relationship between wind Analyze the relationship between wind systems and precipitation systems and precipitation

How do the How do the prevailing winds prevailing winds affect affect precipitation in:precipitation in:

1.1. EnglandEngland2.2. Midwestern U.S.Midwestern U.S.3.3. British ColumbiaBritish Columbia4.4. Northern AfricaNorthern Africa5.5. Central AustraliaCentral Australia Question #26 p. Question #26 p.

67 = great active 67 = great active learning lablearning lab

A - EnglandEngland

B - Midwestern U.S.Midwestern U.S.C - British ColumbiaBritish Columbia

D - Northern AfricaNorthern Africa

E - Central Central AustraliaAustralia