Atmospheric and Oceanic Circulation Chapter Notes | Science for Grade 6 PDF Download

Introduction

The chapter "Atmospheric and Oceanic Circulation" explains how air and water move around our planet. It covers why winds blow, how ocean currents flow, and how these movements affect weather and climate. You will learn about the reasons behind cold water near some coasts, the role of Earth's rotation, and how satellites help us study these patterns. This chapter helps you understand the connection between air, water, and Earth's energy, making it easier to see how our planet's systems work together.

Why does air flow?

• Air is always in motion, and this movement is known as wind.
• In the past, sailors used wind to help navigate and move their ships across the world.
• Today, wind is also used as a renewable source of energy through technologies like wind turbines.
• Earth doesn’t have a giant fan blowing air around the planet.

The Flow of Air

• Air is always moving around the Earth.
• Wind is created when air moves from areas with high pressure to areas with low pressure.
• High pressure happens when air is cooler and sinks, pressing down on the Earth.
• Low pressure happens when air is warmer and rises, creating less pressure on the Earth.

Temperature and Air Pressure

• The Sun heats the Earth unevenly, causing differences in air temperature.
• Warm air rises because it is less dense, and cool air sinks because it is more dense.
• These pressure differences cause winds to blow locally and globally.

What patterns do global winds form?

• Earth has large convection cells that move heat around the planet.
• Convection happens when warm air rises and cool air sinks, creating a cycle.
• Air near the Earth's surface is heated by conduction, making it less dense and causing it to rise.
• This rising air carries heat to higher altitudes, spreading energy around the world.
• Global convection cells create three main wind systems in each hemisphere: trade winds, westerlies, and polar easterlies.

Global Winds

• Trade winds blow near the equator, helping sailors travel across oceans.
• Westerlies blow in the middle latitudes, often moving weather across places like the United States.
• Polar easterlies blow near the poles, where cold air moves away from high pressure areas.
• These wind systems are created by global convection cells and Earth's uneven heating.

Why do the major wind systems blow in certain directions?

Rotation of Earth 

• When something moves across a rotating surface, it appears to curve because the surface is moving underneath it.
• Earth's rotation causes a similar effect on the movement of air and water.
• In the Northern Hemisphere, moving air and water appear to curve to the right. In the Southern Hemisphere, they appear to curve to the left. This curving movement is known as the Coriolis effect.
• The Coriolis effect explains why air and water follow curved paths instead of straight lines.
• This effect is responsible for the curving patterns of wind circulation around the Earth.

How does the Coriolis effect deflect air (and water) on Earth's surface?

• Earth’s rotation causes air to move with it, but the surface moves faster at the equator than at the poles because it has a longer distance to cover in the same 24 hours.
• As air moves from the equator toward the poles, it carries this faster eastward motion. Since the ground beneath is moving more slowly, the air appears to be deflected to the east.
• On the other hand, when air moves from the poles toward the equator, it enters areas where the surface is moving faster. The air seems to lag behind and appears to be deflected to the west, as if Earth’s faster rotation is leaving it behind.

Effect of Landmasses

• The Coriolis effect is not the only thing that influences how wind moves.
• Landmasses also play a role in changing the speed and direction of wind.
• For example, the westerly winds in the Southern Hemisphere are especially strong in some areas because they mostly blow over open oceans with few continents to block or disrupt them.
• When wind comes into contact with a large land feature like a mountain, it is deflected or forced upward, changing its path.

Why do ocean waters flow?

• Ocean water moves because of differences in temperature and salinity (saltiness).
• Cold water and water with high salinity are more dense and sink.
• Warm water and water with low salinity are less dense and rise.
• These differences create currents, which are like rivers in the ocean.

Density Currents

• Density currents are vertical movements of water caused by differences in density.
• High salinity and cold temperatures make water denser, so it sinks.
• These currents move water from the surface to deeper parts of the ocean.
• Density currents form where water becomes colder or saltier, like in the North Atlantic.

Surface Currents

• Surface currents are caused by wind blowing over the ocean's surface.
• Wind transfers energy to the water, making the top layer of the ocean move.
• These currents carry water horizontally across the ocean.

Upwelling

• Upwelling is when cold, deep water rises to the ocean's surface.
• It happens when wind pushes IronSource: https://www.britannica.com/science/upwelling pushes water away from an area, allowing deeper water to come up.
• Upwelling brings nutrient-rich water to the surface, supporting algae, fish, and other sea life.
• Upwelling often happens along coastlines where winds blow parallel to the shore, like off the coast of northern California.

Did You Know?

Surface currents are ocean movements caused by wind. When wind blows across the ocean, it transfers its energy to the water. The moving air particles push against the surface, causing the top layer of the ocean to move horizontally. This is how surface currents form and travel across the ocean!

Why do ocean currents flow in certain directions?

• Cargo spills in the ocean can provide valuable information for oceanographers studying ocean currents.
• When items from these spills wash up on shore, their latitude and longitude help track the direction and speed of the currents.
• These washed-up items serve as clues, showing how and where ocean water is moving.
• One example involves a spill of rubber bath toys that were lost in a January 1992 storm in the North Pacific Ocean.
• By tracking where the toys ended up, scientists were able to gather data about the movement of ocean currents in that region.

Influencing Factors

• Ocean currents form patterns, like air, because of Earth's rotation and landmasses.
• The Coriolis effect makes ocean currents curve, just like winds.
• Landmasses deflect currents, creating large circular systems called gyres.
• Gyres spin clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.
• Warm currents are usually on the western sides of oceans, and cold currents are on the eastern sides because of wind patterns and the Coriolis effect.
• The Sun's energy drives convection in the oceans, moving warm and cold water around.

What global pattern do ocean currents form?

• Ocean currents form a global system called the Great Ocean Conveyor Belt.
• This system combines surface currents, upwelling, and density currents to move heat around the Earth.
• High salinity water cools and sinks in places like the North Atlantic, starting deep currents.
• Deep water rises back to the surface through upwelling, completing the cycle.
• Warm shallow currents and cold, deep, high-salinity currents work together in this system.

A Closer Look: Jason-3 "Sees" the Sea

• Jason-3 is a satellite that uses radar to measure sea surface height, called ocean surface topography.
• Radar sends signals to the ocean and measures how long it takes for them to bounce back.
• This helps calculate the distance to the water's surface accurately, within a few millimeters.
• Jason-3 data show higher-than-normal sea levels in red and lower-than-normal levels in blue.
• These measurements help scientists study ocean currents, sea level changes, and improve weather and climate forecasts.