13.6 Wind and Ocean Currents Science 10

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 that 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?

• Wind is a movement of air in the atmosphere

How Wind Develops• Caused 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?

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

rises creating a low pressure)↓

2. Cool air rushes into 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 Demo Time!!

http://www.youtube.com/watch?v=7xWWowXtuvA

Classifying Winds

I. Localized- affect only small areasTypes of Local Winds• Sea Breezes- from sea to land• Land Breezes- from land to sea

II. Prevailing winds- affect large areas, - types to follow after we look at

what causes prevailing winds

Causes of Prevailing Winds

• Due 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

The Coriolis Effect• Earth’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 Videohttp://www.youtube.com/watch?v=mcPs_OdQOYU

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

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

Effects of Prevailing Winds

• Help 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…)

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

Sooooooo… Do you think the Coriolis Effect

and Wind effect how water moves in the

ocean?

Ocean Currents

Ocean Currents• Mass movement or

flow of ocean water• River within the

ocean• Two types

–SurfaceSurface and DeepDeep

Surface Current• Horizontal, 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

• Red current = warm current• Blue current = cold current

• Surface currents flow in a circular pattern– Northern Hemisphere flows clockwise– Southern Hemisphere flows counter-clockwise– Poles flow in opposite direction

• Notice that the warm currents flow from the equator

Surface Currents

• Controlled by three factors– Prevailing winds = Cause

surface currents to flow in the direction the wind is blowing (top 400 m)

– Coriolis Effect– Continental Deflections =

shape of the land it flows up against

Deep Currents

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

• Caused by changes in density– This change in density is the

result of changing temperature and salinity

Causes, broken down…• Change in temperature

– Decreasing the temperature (it’s colder) of water increases density (water sinks)

• Change in salinity– Increasing the salinity of water increases

density (again, making water sink)– Salinity increases because when water at the

poles freezes, the salt doesn’t freeze so it’s left behind and sinks to the ocean floor and is replaced by new water (hence the current)

Both TEMPERATURE AND SALINITY 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…