SCIENCE 10 Wind and Ocean Currents

A Little Background … Atmospheric Pressure is the pressure the air exerts as gravity pulls it towards 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.

Neat Fact The weight of the air that is pushing down on your shoulders at any given time is equivalent to 1 ton, or about the weight of a fully grown rhino.

What is Wind? Wind is a movement of air in the atmosphere. How Wind Develops Wind is 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!!

Classifying Winds Localized winds are winds affect only small areas. Types of Local Winds  Sea Breezes- from sea to land  Land Breezes- from land to sea Prevailing winds are winds that affect large areas. - They affect weather around the globe.

Causes of Prevailing Winds Prevailing Winds are caused by a combination of convection currents and the Earth’s eastward rotation. Air at the equator is warmed and rises, forming a convection current called the equatorial convection current. This wind moves northward and begins to cool.

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. video Video2

Coriolis cont… This is 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. Prevailing winds 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 anemometer Wind speed indicator – anemometer/weather vane

Class Work Read pages 516 to 519 to review winds. Pay close attention to the Figures 1 and 2 on page 516 and 517. Complete questions:  1 and 2 on page 519 to reinforce what you have learned about wind.

Ocean Currents

Ocean Currents are a mass movement or flow of ocean water. Currents are like a river within the ocean. The reason Norway and Iceland have mild winters is due to ocean currents. Two types  SurfaceDeep  Surface and Deep

Surface Current Surface Currents are 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: 1. Prevailing winds = Cause surface currents to flow in the direction the wind is blowing (top 400 m) 2. Coriolis Effect 3. Continental Deflections = shape of the land it flows up against.

Deep Currents Deep Currents are a stream-like movement of ocean water far below the surface. Caused by changes in density  This change in density is the result of changing temperature and salinity(saltiness)

Causes, in-depth ;) 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 to move and to be replaced (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…