Wind and Ocean Circulation

Why Are Air and Ocean Currents Important? 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: tied to the prevailing wind circulation of the atmosphere; general pattern of these surface currents is a nearly closed system of currents, called gyres

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

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

Winds and Coriolis Effect 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

What is the Coriolis Effect? On the earth, the effect tends to deflect moving objects to the right in the northern hemisphere and to the left in the southern and is important in the formation of cyclonic weather systems The curvature of things moving across the earth as it rotates Click here for video Welcome to Discovery Education Player

Atmospheric Cell Loops 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 Ferrel Cells 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

What are Prevailing Winds 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: Trade winds – blow surface water westward Westerly winds – blow surface water back towards the east Polar winds- the dry, cold prevailing winds that blow from the high-pressure areas of the polar highs at the north and south poles towards low-pressure areas within the Westerlies at high latitudes

Prevailing Winds Latitude/Wind Direction Polar Easterlies Between 60° latitude and the poles; From East to West Mid-latitude Westerlies Between 30° and 60° latitude; From West to East Northeast Trade Winds Near 0°, North of the Equator to 30°N; From Northeast to West Southeast Trade 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. 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 Southern hemisphere, the Earth is rotating clockwise, so the prevailing wind is deflected to the left.

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

Cyclones and Anticyclones 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 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. 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

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: 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

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) The frictional drag on molecules below move the rest of the water at right angles to the wind direction

Ekman spiral describes the speed and direction of flow of surface waters at various depths Factors: Wind Coriolis effect Ekman transport is the overall water movement due to Ekman spiral Ideal transport is 90º from the wind Transport direction (right or left) depends on the hemisphere

GYRES A gyre in oceanography is any large system of rotating ocean currents, particularly those involved with large wind movements. Gyres are caused by the Coriolis Effect planetary vorticity along with horizontal and vertical friction, which determine the circulation patterns from the wind curl (torque). The term gyre can be used to refer to any type of vortex in the air or the sea, even one that is man-made, but it is most commonly used in oceanography to refer to the major ocean systems.

Gyres are large circular-moving loops of water Subtropical gyres Five main gyres (one in each ocean basin): North Pacific South Pacific North Atlantic South Atlantic Indian

Ocean Gyres: large mounds of water and the flow around them Ocean Gyres: large mounds of water and the flow around them. They produce large circular currents in all the ocean basins.

Gyres

Deep Water Circulation (Thermohaline Circulation) These waters make up the other 90% of the ocean Move around the ocean basins by density driven forces and gravity. 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) Surface and deep-water currents are all linked in a global pattern of circulation.

Deep currents Deep currents: Form in subpolar regions at the surface Are created when high density surface water sinks Factors affecting density of surface water: Temperature (most important factor) Salinity Deep currents are also known as thermohaline circulation

Upwelling & Downwelling Upwelling is the movement of cold, deep, often nutrient-rich water to the surface mixed layer; Downwelling is the movement of surface water to deeper depths.

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). 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).

Coastal upwelling & downwelling Ekman transport moves surface water away from shore, producing upwelling Ekman transport moves surface water towards shore, producing downwelling

Upwelling Upwelling occurs when surface waters diverge (move apart), enabling upward movement of water. Upwelling brings water to the surface that is enriched with nutrients important for primary productivity (algal growth) that in turn supports richly productive marine ecosystems. This drives photosynthesis of phytoplankton (tiny alga), which form the base of the ocean food web.

What is Downwelling? When the density of water increases, it sinks below less dense layers of water Downwelling is the process of accumulation and sinking of higher density material beneath lower density material, such as cold or saline water beneath warmer or fresher water or cold air beneath warm air. Upwelling is the opposite process and together these two forces are responsible in the oceans for the thermohaline circulation.

Downwelling 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

Why are downwelling and upwelling important? 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 Warmer water sinks, and picks up more oxygen and nutrients as it cools

Other surface currents Longshore currents Run parallel along coastlines Responsible for formation of barrier islands and transport of sand along beaches Rip currents Occur when coastal waves or currents converge Dangerous for swimmers because they flow off the beach towards the open ocean

Global Conveyor Belt The ocean is not a still body of water. There is constant motion in the ocean in the form of a global ocean conveyor belt. This motion is caused by a combination of thermohaline currents (thermo = temperature; haline = salinity) in the deep ocean and wind-driven currents on the surface. Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface.

Global Conveyor 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) Water from the equator continues to move toward the poles 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 Click here for simulation Click here for animation

The Great Pacific Garbage Patch What is it? Island of Floating Plastic; thought to be twice the size of Texas.. But size is still debated made up of widely dispersed, broken-down plastic waste particles When plastic bottles, cups and bags are dropped in the street, rain washes them into storm sewers, rivers and eventually the ocean Stuck in the North Pacific gyre, circulating it swirls around until sunlight and salt water break it down into small plastic chips. With millions of tons of such trash in the North Pacific Gyre, the water now resembles “plastic soup,” Fish and birds mistake the plastic bits for food, resulting in death by poisoning or digestive blockage. Plastic also absorbs pollutants like banned PCBs, or polychlorinated biphenyls, once widely used in electrical equipment. When we eat contaminated fish, we ingest these harmful chemicals http://education.nationalgeographic.com/education/encyclopedia/great-pacific-garbage-patch/?ar_a=1

Ocean Currents http://www.youtube.com/watch?v=Hu_Ga0JYFNg NASA | The Ocean: A Driving Force for Weather and Climate https://www.youtube.com/watch?v=6vgvTeuoDWY