Wind and Ocean Circulation currents.swf currents.swf

Why Are Air and Ocean Currents Important? Oceans are important to the earth’s climate Oceans are important to the earth’s climate –They redistribute heat around the globe –They absorb heat, helping to regulate the earth’s temperature –Air and Ocean currents work hand-in-hand

Ocean Currents are influenced by two types of forces 1. Primary Forces--start the water moving The primary forces are: 1. Solar Heating- cause water to expand 2. Winds- blows on surface, push water 3. Gravity- pull water down “hill” 4. Coriolis- intervenes and causes water to move to the right, around mound of water 2. Secondary Forces--influence where the currents flow 1. Surface Circulation

Winds Unequal heating by the sun causes differences in air pressures. Unequal heating by the sun causes differences in air pressures. Cold air drops while warm air rises. Cold air drops while warm air rises.

Warm air expands = low pressure because it is spread out and less dense Warm air expands = low pressure because it is spread out and less dense Cold air sinks = high pressure because it is compact and more dense Cold air sinks = high pressure because it is compact and more dense

Winds and Coriolis Effect This causes a circulation of air to occur in a north-to- south direction This causes a circulation of air to occur in a north-to- south direction However, the Coriolis effect deflects these winds, so wind patterns are a bit more complicated However, the Coriolis effect deflects these winds, so wind patterns are a bit more complicated

What is the Coriolis Effect? The curvature of things moving across the earth as it rotates The curvature of things moving across the earth as it rotates Click here for videoWelcome to Discovery Education Player Click here for videoWelcome to Discovery Education PlayerWelcome to Discovery Education PlayerWelcome to Discovery Education Player

Atmospheric Cell Loops There are 3 atmospheric cell loops that exist: There are 3 atmospheric cell loops that exist: –Hadley Cells Warm air rises near the equator, cools, falls in the subtropics, then goes back to the equator Warm air rises near the equator, cools, falls in the subtropics, then goes back to the equator –Ferrel Cells Air rises in sub-polar regions, cools and falls in the sub-tropics, then moves toward the poles Air rises in sub-polar regions, cools and falls in the sub-tropics, then moves toward the poles –Polar Cells Air descends at the poles and moves toward the equator Air descends at the poles and moves toward the equator

What are Prevailing Winds? Prevailing Winds are winds that affect large areas, therefore affecting weather around the whole world. Due to the Earth rotating, the direction of prevailing winds form a unique pattern. Three main prevailing winds: Three main prevailing winds: –Trade winds – blow surface water westward –Westerly winds – blow surface water back towards the east –Polar winds

Prevailing Winds Latitude/Wind Direction Polar Easterlies Between 60° latitude and the poles; From East to West Polar Easterlies Between 60° latitude and the poles; From East to West Mid-latitude Mid-latitude Westerlies Between 30° and 60° latitude; From West to East Westerlies Between 30° and 60° latitude; From West to East Northeast Trade Northeast Trade WindsNear 0°, North of the Equator to 30°N; From Northeast to West WindsNear 0°, North of the Equator to 30°N; From Northeast to West Southeast Trade Southeast Trade Winds Near 0°, South of the Equator to 30° ;From Southeast to West Winds Near 0°, South of the Equator to 30° ;From Southeast to West

The Coriolis Effect on Prevailing Winds As the Earth rotates, the path of prevailing winds is deflected. As the Earth rotates, the path of prevailing winds is deflected. Since the Earth rotates to the East... In the Northern hemisphere, the Earth is rotating counterclockwise, so the prevailing wind is deflected to the right. In the Northern hemisphere, the Earth is rotating counterclockwise, so the prevailing wind is deflected to the right. In the Southern hemisphere, the Earth is rotating clockwise, so the prevailing wind is deflected to the left. In the Southern hemisphere, the Earth is rotating clockwise, so the prevailing wind is deflected to the left.

Cyclones and Anticyclones Anticyclones occur where cooler air sinks and a zone of high atmospheric pressure develops Anticyclones occur where cooler air sinks and a zone of high atmospheric pressure develops –These form at subtropical latitudes Cyclones occur where warm air rises, and areas of low pressure develops Cyclones occur where warm air rises, and areas of low pressure develops –These form at the equator and at sub-polar latitudes

How are winds and oceans linked? Cyclones and anticyclones create linked, circulating wind patterns which continually move and change. Cyclones and anticyclones create linked, circulating wind patterns which continually move and change. The Coriolis effect causes them to spin, either clockwise or counterclockwise, depending on the hemisphere they occur in. The Coriolis effect causes them to spin, either clockwise or counterclockwise, depending on the hemisphere they occur in. These winds move over the ocean surfaces and cause ocean surface currents These winds move over the ocean surfaces and cause ocean surface currents

Coastal Breezes Land heats up faster than water. Warm air rises over land, and moves toward the sea. Cooler air from the sea is lower, and moves over the land. This causes coastal breezes. Onshore breezes blow from the land Offshore breezes blow from the sea

Ocean Currents There are two types of ocean currents: There are two types of ocean currents: –Surface currents, which are caused by winds –Deeper ocean currents, which are caused by changes in density as a result of changing temperature and salinity

Surface Currents (Surface Circulation) These waters make up about 10% of all the water in the ocean. These waters make up about 10% of all the water in the ocean. Are the upper 400 meters of the ocean. Are the upper 400 meters of the ocean. Important to climate of the earth Important to climate of the earth –Transport heat energy from tropics to cooler parts of the globe –Impact shipping and fishing industries as well

How do surface currents work? The Ekman Spiral As the wind blows, the molecules on the very surface of the ocean are moved at an angle (not in the same direction as the wind) As the wind blows, the molecules on the very surface of the ocean are moved at an angle (not in the same direction as the wind) The frictional drag on molecules below move the rest of the water at right angles to the wind direction The frictional drag on molecules below move the rest of the water at right angles to the wind direction

Ocean Gyres: large mounds of water and the flow around them. They produce large circular currents in all the ocean basins. There are 5 gyres – places where currents meet

Gyres

Deep Water Circulation Deep Water Circulation (Thermohaline Circulation) These waters make up the other 90% of the ocean These waters make up the other 90% of the ocean Move around the ocean basins by density driven forces and gravity. Move around the ocean basins by density driven forces and gravity. driven by changes in density driven by changes in density –The density difference is a function of different temperatures and salinity –They sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase. –A result of thermohaline processes (changes in temperature or salinity) Some are vertical, moving water upward and downward to and from the surface (upwelling and downwelling) Some are vertical, moving water upward and downward to and from the surface (upwelling and downwelling) Surface and deep-water currents are all linked in a global pattern of circulation. Surface and deep-water currents are all linked in a global pattern of circulation.

The effect of winds on the vertical movement of water Upwelling along the coast caused by Ekman transport of waters (waters move to the right of the wind). Upwelling along the coast caused by Ekman transport of waters (waters move to the right of the wind). –The waters moved offshore are replaced by waters from below. This brings cold, nutrient rich waters to the surface Downwelling caused by Ekman transport onshore (movement of water to the right of the wind direction). Downwelling caused by Ekman transport onshore (movement of water to the right of the wind direction).

What is Downwelling? When the density of water increases, it sinks below less dense layers of water When the density of water increases, it sinks below less dense layers of water –(remember that density increases as temperature and salinity increases?)

Downwelling Caused or occurs as a result of 3 situations: Caused or occurs as a result of 3 situations: – thermohaline processes –Also caused when a current hits a coast –Also occurs beneath mounds of water that form in the middle of anticyclones and gyres –Click here for animation Click here for animationClick here for animation

Upwelling Occurs as a result of the same conditions that cause downwelling Occurs as a result of the same conditions that cause downwelling Where downwelling occurs, water must rise to replace it Where downwelling occurs, water must rise to replace it When the wind blows surface water away from a coastline, water upwells to replace the water that left When the wind blows surface water away from a coastline, water upwells to replace the water that left Click here for animation Click here for animation Click here for animation Click here for animation

Why are downwelling and upwelling important? They are needed to revitalize the nutrient and oxygen content in the oceans of the earth They are needed to revitalize the nutrient and oxygen content in the oceans of the earth Nutrients and oxygen are brought up from deeper parts of the oceans with cooler water Nutrients and oxygen are brought up from deeper parts of the oceans with cooler water Warmer water sinks, and picks up more oxygen and nutrients as it cools Warmer water sinks, and picks up more oxygen and nutrients as it cools

Global Conveyor Colder water at the poles sinks, and moves toward the equator. Colder water at the poles sinks, and moves toward the equator. As the water warms, it becomes less dense, and rises at the equator (upwelling) As the water warms, it becomes less dense, and rises at the equator (upwelling) Water from the equator continues to move toward the poles Water from the equator continues to move toward the poles As water cools near the poles, it becomes more dense and sinks (downwelling) As water cools near the poles, it becomes more dense and sinks (downwelling) It takes 1000 years for water to make one loop around the planet It takes 1000 years for water to make one loop around the planet Click here for simulation Click here for simulation Click here for simulation Click here for simulation Click here for animation Click here for animation Click here for animation Click here for animation

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