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Boardworks Middle School Science Wind and Ocean Currents

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Presentation on theme: "Boardworks Middle School Science Wind and Ocean Currents"— Presentation transcript:

1 Boardworks Middle School Science Wind and Ocean Currents

2 Boardworks Middle School Science Wind and Ocean Currents
Convection currents Boardworks Middle School Science Wind and Ocean Currents Local weather is affected by the movement of air masses all over the world. Some of this movement happens because the Sun heats the surface of the Earth unevenly. Temperature differences in the air cause convection currents. Convection currents in the atmosphere move warm air into colder areas. These wind currents take place anywhere there are temperature differences in the air. This often happens in places with nearby water. Teacher notes Students should have mastered the information in What is Weather.ppt before viewing this presentation.

3 Sea breezes and land breezes
Boardworks Middle School Science Wind and Ocean Currents Teacher notes This three-stage animation explains how and why convection currents occur at coastal regions. It also explores how temperature differences between land, water and air affect the weather. Red arrows are used to represent the movement of warm air and blue arrows are used to represent the movement of cooler air. Suitable prompts include: Stage 1: Why is the hot air rising? Stage 2: What happens to the warmer air as it moves out to the ocean? Stage 3: Why has the convection current changed direction?

4 Boardworks Middle School Science Wind and Ocean Currents
Nearby water Boardworks Middle School Science Wind and Ocean Currents Air, land and water all absorb heat differently. Water is better at conserving heat than air or land. When it is hot outside, deep, cold water keeps the overall temperature of the water low. This cools the air above the water. The cool air moves ashore, lowering the land temperature. When it is cold outside, water holds its heat better than land. The warm water releases heat into the air. This warm air moves ashore, raising the land temperature. Photo credit: National Oceanic and Atmospheric Administration This image represents the surface temperatures in the Gulf of Mexico on January 12, The turquoise sections closest to the Florida coast represents water of approximately 16°C, about 61°F. The yellow sections are about 23°C, and the orange sections are approximately 25°C. Teacher notes: Along with the oceans, the Great Lakes serve as significant heat sinks for the surrounding land. The Lakes also contribute a great deal of moisture to the air, resulting in humid conditions and snow belts on their downwind shores.

5 The rotation of the Earth
Boardworks Middle School Science Wind and Ocean Currents Teacher notes To help students visualize the impact of the Coriolis effect, it might be useful to explain that the wind deflects ‘right’ in the Northern Hemisphere or ‘left’ in the Southern Hemisphere (stages two and four) if an individual is standing on the surface of the Earth, in that Hemisphere, and facing the equator.

6 Boardworks Middle School Science Wind and Ocean Currents
Heating of the Earth's surface and atmosphere by the Sun also drives convection in the oceans, producing ocean currents. There are two circulation systems in the ocean: surface currents surface currents – this occurs in the upper part of the ocean. This involves just the top 10% of the water in the ocean. 400 m deep currents deep currents – this occurs below 400 meter depth.

7 What causes ocean currents?
The Earth’s oceans are all connected to form one big ocean. Ocean currents move water around the world, affecting global and local weather. There are many factors that affect ocean currents. Wind can cause the surface of the ocean to move, which can move the layers below. The rotation of the Earth affects ocean currents the same way it affects air currents. The Coriolis effect can shift the flow of ocean currents to the right or left of its intended destination.

8 Global ocean conveyor belt
Boardworks Middle School Science Wind and Ocean Currents Water’s temperature and density also affect its movement. Cold water is denser than warm water. The dense water sinks, starting a deep current that moves water around the world. This is often called the global ocean conveyor belt. Photo credit: Science Photo Library Satellite image of the Earth from space with a map of ocean circulation. Teacher notes You may choose to explain the role of salinity in water density. As polar sea ice forms, the salt is left behind, increasing the concentration of salt in the coldest parts of the ocean. The salty cold water is more dense than warm, fresh water and sinks to the ocean floor, pushing water through the world’s ocean like a plunger. The global conveyor belt is thought to play a fundamental part in the regulating the Earth’s climate, as it transfers heat and moisture around the planet. Some scientists predict that if this global circulation was to stop, temperatures in certain regions (including Europe) could decrease rapidly. It is thought to have stopped or changed direction in the past, causing significant changes in global temperatures.

9 Ocean currents and weather
Boardworks Middle School Science Wind and Ocean Currents The movements of ocean currents can have a major effect on global and local weather. Ocean currents can move streams of warm or cool water thousands of miles, warming or cooling the air above them. Teacher notes The direction of ocean currents is determined by factors including wind, the Earth’s rotation, and water density and temperature differences. In some places, wind blows surface water away, resulting in the upwelling of deeper, colder water that then cools surrounding air and land. The occurrence of this phenomenon off the Pacific coast of the U.S. contributes to the moderate average temperatures of San Francisco. For example, the Gulf Stream moves warm water from the Gulf of Mexico to the northern Atlantic around Western Europe. This means that the average temperature of London, England is not much colder than that of San Francisco, CA, despite being much farther from the equator.

10 Boardworks Middle School Science Wind and Ocean Currents
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