WINDS

Understand the cause of wind and how they affect 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 to low

Know that air blows from areas of high pressure to areas of low pressure. The statement is fact. Think:

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 Breeze

Using your knowledge of wind predict & explain the wind direction below. P. 61

• FACT: Water holds heat longer than the land.

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

• Air rises over sea

• Relative Low pressure over sea

• 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

Winds

Preva

iling

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

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 rainfall p. 66

A relatively warm, moist air blows off the sea It is forced up by mountains (high relief) Air cools at higher altitude Cool air holds less moisture Consequently clouds condense and rain falls 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 Warm Moisture laden air cools at higher altitude Cool air holds less moisture Consequently clouds condense and rain falls

• 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) Warm Moisture laden air cools at higher altitude Cool air holds less moisture Consequently clouds condense and rain falls

• 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:

1. Argentina

2. Columbia

3. Baffin Island

4. Newfoundland

A

B

C

D

Analyze the relationship between wind systems and precipitation

How do the prevailing winds affect precipitation in:

1. England2. Midwestern U.S.3. British Columbia4. Northern Africa5. Central Australia Question #26 p.

67 = great active learning lab

A

B

C

D

E