13.6 Wind and Ocean 13.6 Wind and Ocean Currents Currents Science 10

Wind

Wind Patterns

A Little Background …A Little Background …Atmospheric Pressure is the

force of the air pressing down on the earth’s surface◦ Atmospheric pressure is

measured using a barometer.◦ Since air molecules are so

spread out (lots of empty space), we don’t feel the pressure they exert

Differences in air pressure help cause winds and affect air masses. They are also factors in the formation of storms such as thunderstorms, tornadoes and hurricanes.

What is Wind?What is Wind?Wind is a movement of air in the atmosphereHow Wind DevelopsCaused by a difference in air pressure due to

unequal heating of the atmosphere. Question:

Where on the planet does the surface get heated more than other areas?

At the Earth’s surface, wind always blows from areas of high pressure to areas of low pressure

How are Winds Created?How are Winds Created?Winds are created by….1. Heating the air, decreases pressure (warm air

rises creating a low pressure)↓

2. Cool air rushes in to replace the warm air(cooler dense air, produces high pressure)

↓ 3. As air goes from high to low pressure winds

form

This is a CONVECTION style… Convection Current

Make your own ‘How are Winds Created?’ Graphic

Classifying Winds Classifying Winds I. Localizedaffect only small areasTypes of Local WindsSea Breezes- from sea to landLand Breezes- from land to sea

II. Prevailing windsaffect large areas, types to follow..

Which one do you think affects us more?...

Coriolis Effect & Causes of Coriolis Effect & Causes of Prevailing Winds JigsawPrevailing Winds JigsawFirst: become an expert (5-10

minutes)◦Read notes/text◦Discuss within your group◦Determine how to teach others (as a

group)Next: switch with another group (A-D,

B-E, C-F) and teach each other◦Take turns teaching content◦Take notes on Coriolis effect / causes of

prevailing winds

The Coriolis EffectThe Coriolis EffectEarth’s rotation causes anything

that moves LONG DISTANCES, such as prevailing winds, to APPEAR to change directions.

The apparent change in direction of a moving object in a rotating system is called the CORIOLIS EFFECT.

Demo Video

Coriolis cont…Coriolis cont…Evident on the Earth because as Earth

rotates eastward, an object travelling from north to south will appear to move to the right

In the southern hemisphere objects moving from the pole appear to move to the left

The Coriolis effect is more predominant closer to the poles

Let’s look at this effect on the globe

Causes of Prevailing Causes of Prevailing WindsWindsDue to a combination of convection currents and coriolis effect

air at the equator is warmed and rises, forming a convection current called the equatorial convection current

Effects of Prevailing WindsEffects of Prevailing WindsHelp distribute large amounts of

solar energy from the equator to the colder parts of the world.

Also carry moisture, causing a variety of precipitation (snow, rain, etc…)

Prevailing Wind Terms:Prevailing Wind Terms:Polar easterlies – occur between 60

degrees latitude and the poles and moves east to west

Mid-latitude westerlies – occurs between 30 degrees and 60 degrees latitude and move from west to east

Northeast trade winds – occur just north of the equator and move east to west

Southeast trade winds – occur just south of the equator and move east to west

Label these on your map

Wind terms cont…Wind terms cont…• Gusts – occur because of a rapid

air pressure change and move in no fixed direction

• Squalls – gusts accompanied by rain

• Wind speed indicator – anemometeranemometer/weather vane

So… So… Do you think the Do you think the Coriolis EffectCoriolis Effect and and WindWind affect how water affect how water moves in the ocean?moves in the ocean?-Take 1 min to discuss -Take 1 min to discuss with a student at your with a student at your table, I will get feedback table, I will get feedback from some of you!from some of you!

Ocean CurrentsOcean Currents

Ocean CurrentsOcean Currents•Mass movement or flow of ocean water• River within the ocean• Two types –SurfaceSurface and DeepDeep

Surface CurrentSurface CurrentHorizontal, stream-like movements of water that occur at or near the surface of the ocean

Can reach depths of several hundred meters

Surface Current Animation

Surface CurrentsSurface Currents

Controlled by three factors◦Prevailing winds = Cause surface currents to flow in the direction the wind is blowing

◦Coriolis Effect◦Continental Deflections = shape of the land it flows up against

Deep CurrentsDeep Currents

Stream like movement of ocean water far below the surface. THIS IS WAY DOWN THERE!

Caused by changes in density◦Change in temperature◦Change in salinity (Salt in the water)

Causes, broken down…Causes, broken down… Change in temperature

◦ Decreasing the temperature of water increases density (water sinks… remember demo?)

Change in salinity◦ Increasing the salinity of water increases density

(again, making water sink)

Both of the above causes warmer less dense water from the equator moves to replace it (water will always want to be level and that is why the water that leaves gets replaced)

The Pic on the next page does a good job explaining this

phenomena…

Text (page 519 #1-4, 521 Text (page 519 #1-4, 521 #1-2)#1-2)

1. a) Northward b) northward c) to the right

2. A) the southeast trade winds: solar energy strikes most directly near the equator. This causes the land, water and air there to heat. The hot air rises and moves southward to about 30oS latitude. The rising moist air is replaced by the cooler, drier air (convention current). At the same time, the Coriolis effect causes the winds to twist to the left. This results in the southeast trade winds

2B mid-latitude westerlies: at 30oS, some of the cool, decending air joins with the mid-latitude convection currents to flow southward. These winds also twist to the left, causing the mid-latitude westerlies

2C Polar easterlies: cold, dense air flows northward from the area around the south pole. It also twists to the left, causing the polar easterlies

2D Southern Hemisphere jet streams: caused by pressure differences at the upper levels of the atmosphere. Air pushed from the equator to 30oS twists leftward, causing an upper airflow to the east.

3. Along which latitude in the Southern Hemisphere are deserts likely to be found? Explain why this happens.◦ Most likely to be found at 30oS latitude –

this is because the air descending from the convection currents is cool and dry

◦ Southern hemisphere deserts: Victoria and Gibson deserts (Australia); Namib desert (Namibia)

4. You would fly high enough to join the jet stream because it travels from west to east at a high speed and would help the plane fly faster