WINDS

Understand the cause of wind and

how it affects climate

Chapter 4

Pages 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)

Know that air blows from areas of high

pressure to areas of low pressure.

The statement is fact.

Real examples:

1. Air inside a balloon

2. Exhaling

3. Air powered pellet gun

It is simply fact.

High and low pressures in the earth’s

atmosphere are responsible for wind

P. 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

wind. 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

Describe how the coriolis force

affects wind 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 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

to 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

Definitions 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

rainWarm, moist air

FRONT

Describe 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

systems and temperature.

How do the

prevailing winds

affect

temperature in:

Columbia

Baffin Island

Newfoundland

A - Columbia

B -Baffin Island

C - Newfoundland

Analyze the relationship between wind

systems and precipitation

How do the prevailing winds affect precipitation in:

1. England

2. Midwestern U.S.

3. British Columbia

4. Northern Africa

5. Central Australia

Question #26 p. 67 = great active learning lab

A - England

B - Midwestern U.S.

C - British Columbia

D - Northern Africa

E - Central Australia