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the Ocean and the Atmosphere The atmosphere affects the oceans and is in turn influenced by them. The action of winds blowing over the ocean surface creates waves and the great current systems of the oceans. When winds are strong enough to produce spray and whitecaps, tiny droplets of ocean water are thrown up into the atmosphere where some evaporate, leaving microscopic grains of salt buoyed by the turbulence of the air. These tiny particles may become nuclei for the condensation of water vapor to form fogs and clouds. The interaction of ocean and atmosphere moderates surface temperatures, shapes Earth''s weather and climate, and creates most of the sea''s waves and currents. Tests ATMOSPHERE-OCEAN and Publications composition and properties of the atmosphere Interactions between gases and particles occur throughout the Earth''s atmosphere and have consequences such as the formation of acid rain and the destruction of stratospheric ozone. To understand how these processes occur in our highly complex atmosphere, our research group studies heterogeneous (gas/surface) interactions in a controlled laboratory setting. By carefully varying parameters such as temperature, relative humidity, and particle composition, we can isolate the response due to changes in each of these conditions in the real atmosphere. Our results can then be used in an integrated analysis with field measurements and modeling studies to produce a more complete understanding of our environment and to predict how future changes in temperature or particulates may, in turn, affect the chemistry of the atmosphere. Water vapor Air Mass Air-Sea Interaction Oceanography 320 Spring 2008 Chapter Objectives Describe the causes of uneven solar heating on Earth. Understand why Earth has seasons and how seasonal changes in solar energy affect atmospheric temperature, pressure, and density. Explain the nature, origin, and consequences of the Coriolis effect in both the Northern and Southern Hemisphere. Discuss the locations and characteristics of Earth''s major atmospheric circulation cells, pressure belts, wind belts, and boundaries. Chapter Objectives Know the difference between weather (meteorology) and climate (climatology). Indicate the conditions required for the formation of tropical cyclones (hurricanes) and explain what types of destruction are caused by them. Describe the cause of Earth''s greenhouse effect and why it has increased in the recent past. Overview Atmosphere and ocean one interdependent system Solar energy creates winds Winds drive surface ocean currents and waves Examples of interactions: El Niсo-Southern Oscillation Greenhouse effect El Niсo and La Niсa Seasons EarthЎs axis of rotation tilted with respect to ecliptic Tilt responsible for seasons Vernal (spring) equinox Summer solstice Autumnal equinox Winter solstice Seasonal changes and day/night cause unequal solar heating of EarthЎs surface Seasons Uneven solar heating Angle of incidence of solar rays per area Equatorial regions more heat Polar regions less heat Thickness of atmosphere Albedo Day/night Seasons Oceanic heat flow High latitudes More heat lost than gained Albedo of ice High incidence of solar rays Low latitudes More heat gained than lost 1 2 3 4 5 6 7 8 9 10 11 12 Air Masses and Frontal Transitional Zones Cold front Weather front Warm front Glossaru of Meteorology A shallow, wispy, smoke-like fog formed when cold air passes over warmer water, and is rapidly heated. Convection currents carry moisture upwards, which quickly recondenses to form fog. Steam fog is common in winter over rivers where the air is more than 10 ўXC colder than the water. Adiabatic process Humidity and Stability Hydrological cycle: a continuous transfer of water among terrestrial, oceanic, and atmospheric reservoirs. Within the atmosphere, water exists in all three forms: i) water vapor, ii) liquid (i.e. cloud droplets, raindrops), and iii) solid (i.e. ice crystals). Within the usual range of temperature and pressure, all three phases of water coexist (equilibrium). Water molecules continuously change their phases. On the average, the residence time of a water molecule is about 10 days. The total amount of water within the atmosphere is very small. In fact, if all water were removed from the atmosphere as rain and distributed over the globe, the water would have only about 2.5 cm (1 in.) depth on the Earth''s surface. Evaporation (Condensation): a process by which water changes phase from a liquid (vapor) to a vapor (liquid). Transpiration: a process by which water absorbed by plant roots eventually escapes as vapor though the surface of green leaves. On land, transpiration is often more important than direct evaporation from the surfaces of lakes, streams, and the soil. Evaportranspiration: direct evaporation + transpiration Sublimation (Deposition): a process by which water changes phase from a solid (vapor) to a vapor (solid). Precipitation: drizzle, rain, snow, ice pellets, and hail; a process by which major portion of atmospheric water returns to the Earth''s surface. Global water budget: the balance sheet for the inputs and outputs of water to and from the various global reservoirs. Precipitation and evaporation are the two major components of the global water budget. Precipitation over land exceeds evaporation annually and vice versa is true over the oceans. The net gain (loss) of water over land (oceans) is balanced with a net flow of water from land to sea. Precipitation falling on land evaporates, infiltrates the ground, or run off as rivers and streams. The ratio of infiltrating the ground to running off depends on the intensity of precipitation and on the vegetation, topography, and the physical properties of the surface. the thermodynamic process The Earth''s Atmosphere By Kshudiram Saha Atmosphere, Weather, and Climate By Roger Graham Barry, Precipitation Atmospheric circulation The Water Cycle: Precipitation Atmospheric circulation ATMOSPHERIC CIRCULATION; WEATHER SYSTEMS solar heating and latitude Topics: Basic topics in atmospheric sciences: structure (layering: pressure, temperature and moisture) and composition of the atmosphere, solar radiation, atmospheric circulation, seasons, weather, climate, global warming, ozone ЎholeЎЁ, pollution, acid rain ATMOSPHERIC CIRCULATION Uneven Solar Heating and the Seasons uneven solar heating and Atmosphere Circulation Climate El Nino and La Nina El Nino and La Nina El Nino and La Nina How El Nino and La Nina affect U.S. storms uneven solar heating Uneven solar heating causes convection currents to form in the atmospherer. The direction of air flow in these currents is influenced by the rotation of Earth. Coriolis Effect: Coriolis Effect: he Coriolis effect and atmospheric circulation cells Atmospheric Circulation Global Scale Circulation of the Atmosphere Vocabulary air mass A large mass of air with nearly uniform temperature, humidity, and density throughout. atmosphere The envelope of gases that surround a planet and are held to it by the planetЎs gravitational attraction. atmospheric circulation cell Large circuit of air driven by uneven solar heating and the Coriolis effect. Three circulation cells form in each hemisphere. climate The long-term average of weather in an area. convection current A single closed-flow circuit of rising warm material and falling cool material. Coriolis effect The apparent deflection of a moving object from its initial course when its speed and direction are measured in reference to the surface of the rotating Earth. The object is deflected to the right of its anticipated course in the Northern Hemisphere and to the left in the Southern Hemisphere. The deflection occurs for any horizontal movement of objects with mass and has no effect at the equator. cyclone A weather system with a low-pressure area in the center around which winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Not to be confused with a tornado, a much smaller weather phenomenon associated with severe thunderstorms. doldrums The zone of rising air near the equator known for sultry air and variable breezes. extratropical cyclone A low-pressure mid-latitude weather system characterized by converging winds and ascending air rotating counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. An extratropical cyclone forms at the front between the polar and Ferrel cells. Ferrel cell The middle atmospheric circulation cell in each hemisphere. Air in these cells rises at 60o latitude and falls at 30o latitude. front The boundary between two air masses of different density. The density difference can be caused by differences in temperature and/or humidity. frontal storm Precipitation and wind caused by the meeting of two air masses, associated with an extratropical cyclone. Generally, one air mass will slide over or under the other, and the resulting expansion of air will cause cooling and consequently rain or snow. geographical equator 0ўX latitude, an imaginary line equidistant from the geographical poles. Hadley cell The atmospheric circulation cell nearest the equator in each hemisphere. Air in these cells rises near the equator because of strong solar heating there and falls because of cooling at about 30o latitude. heat budget An expression of the total solar energy received on Earth during some period of time and the total heat lost from Earth by reflection and radiation into 2 space through the same period. horse latitudes Zones of erratic horizontal surface air circulation near 30oN and 30oS latitudes. Over land, dry air falling from high altitudes produces deserts at these latitudes (for example, the Sahara). hurricane A large tropical cyclone in the North Atlantic or eastern Pacific, whose winds exceed 118 kilometers per hour. intertropical convergence zone (ITCZ) The equatorial area at which the trade winds converge. The ITCZ usually lies at or near the meteorological equator; also called the doldrums. land breeze Movement of air off shore as marine air heats and rises. meteorological equator The irregular imaginary line of thermal equilibrium between hemispheres. It is situated about 5_ north of the geographical equator, and its position changes with the seasons, moving slightly north in northern summer. Also called the thermal equator. monsoon A pattern of wind circulation that changes with the season. Also, the rainy season in areas with monsoon wind patterns. polar cell The atmospheric circulation cell centered over each pole. precipitation Liquid or solid water that falls from the air and reaches the surface as rain, hail, or snowfall. sea breeze Onshore movement of air as inland air heats and rises. storm Local or regional atmospheric disturbance characterized by strong winds often accompanied by precipitation. storm surge An unusual rise in sea level as a result of the low atmospheric pressure and strong winds associated with a tropical cyclone. Onrushing seawater precedes landfall of the tropical cyclone and causes most of the damage to life and property. thermal equilibrium The condition in which the total heat coming into a system (such as a planet) is balanced by the total heat leaving the system. tornado Localized, narrow, violent funnel of fast-spinning wind, usually generated when two air masses collide; not to be confused with a cyclone. trade winds Surface winds within the Hadley cells, centered at about 15o latitude, that approach from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere. tropical cyclone A weather system of low atmospheric pressure around which winds blow counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. It originates in the tropics within a single air mass, but may move into temperate waters if the water temperature is high enough to sustain it. Small tropical cyclones are called tropical depressions, larger ones tropical storms, and great ones hurricanes, typhoons, or willi-willis, depending on location. water vapor The gaseous, invisible form of water. weather The state of the atmosphere at a specific place and time. Six-cell circulation model Wind Patterns Global Ocean Currents Ekman Spiral El Niсo Normal & El Niсo Circulation Monitoring the Atmosphere and Ocean The Atmospheric Connection El Niсo and La Niсa Sea Surface Temperatures Recorded The Wider Effects of El Niсo Global Wind Patterns The region of Earth receiving the Sun''s direct rays is the equator. Here, air is heated and rises, leaving low pressure areas behind. Moving to about thirty degrees north and south of the equator, the warm air from the equator begins to cool and sink. Between thirty degrees latitude and the equator, most of the cooling sinking air moves back to the equator. The rest of the air flows toward the poles. The air movements toward the equator are called trade winds- warm, steady breezes that blow almost continuously. The Coriolis Effect makes the trade winds appear to be curving to the west, whether they are traveling to the equator from the south or north. The trade winds coming from the south and the north meet near the equator. These converging trade winds produce general upward winds as they are heated, so there are no steady surface winds. This area of calm is called the doldrums. Between thirty and sixty degrees latitude, the winds that move toward the poles appear to curve to the east. Because winds are named from the direction in which they originate, these winds are called prevailing westerlies. Prevailing westerlies in the Northern Hemisphere are responsible for many of the weather movements across the United States and Canada. At about sixty degrees latitude in both hemispheres, the prevailing westerlies join with polar easterlies to reduce upward motion. The polar easterlies form when the atmosphere over the poles cools. This cool air then sinks and spreads over the surface. As the air flows away from the poles, it is turned to the west by the Coriolis effect. Again, because these winds begin in the east, they are called easterlies. Many of these changes in wind direction are hard to visualize. Complete this exercise to see the pattern of the winds. SAN FRANCISCO BAY WIND PATTERNS Antarctic water Wind Pattterns Polar cell ferrel cell Hadley cell Doldrums Westerlies Intertropical convergence zone itcz Horse latitudes Trade winds Monsoon Sea and Land Breezes Storm Cyclone Hurricane (Tropical Cyclone) Tropical cyclones, the most powerful of Earth''s atmospheric storms, occur within a single humid air mass Tornado Extratropical cyclone Large storms are spinning areas of unstable air that develop between or within air masses. Extratropical cyclones originate at the boundary between air masses. Frontal storms Storm surge Polar front Extratropical storms "Extratropical" means the storms originate outside the tropics Extratropical Cyclones and Anticyclones Extratropical Cyclones ѓе A cyclone is any circulation around low pressure ѓе ЎExtratropicalЎЁ means outside of the tropics ѓе An extratropical cyclone is a large low pressure system that often forms in the mid-latitudes Norwegian Cyclone Model ѓе Bjerknes developed the typical life cycle of an extratropical cyclone by looking at weather maps ѓе Step 1: The polar front separates warm air and cold air ѓе Step 2: A Ўfrontal waveЎЁ develops ѓе Step 3: Counterclockwise circulation intensifies causing a warm front to the east and a cold front to the west of the wave apex ѓе Step 4: The circulation intensifies until an occlusion happens (now at its strongest) ѓе Step 5: Surrounded by cold air, the cyclone dissipates as a Ўcut-off cycloneЎЁ Step 1: Polar Front Step 2: Open Wave Develops Step 3: Cyclonic Circulation Step 4: Occlusion Step 5: Cut-Off Cyclone What Causes Step 2?! ѓе Why does that initial wave form along the polar front? ѓе Bjerknes didnЎt know because he only had surface weather maps ѓе The answer lies in the upper levels ѓе Cyclogenesis ЎV the formation of a cyclone ѓе Key Ingredients for cyclogenesis: ЎV Surface temperature gradients (front) ЎV Strong jet stream ЎV Presence of mountains or other surface boundaries Baroclinic Instability ѓе Tilted pattern of rising air and sinking air that liberates energy for a cyclone ѓе Warm air rising can lead to the formation of clouds and precipitation ѓе Typical regions of cyclogenesis and paths of cyclones varies from season to season Cyclone Types ѓе Panhandle Hooks ЎV forms in the panhandle region and curves northeastward ѓе NorЎEasters ЎV winter cyclones that move up the eastern Atlantic states ѓе Pineapple Express ЎV jet stream from Hawaii causing storms in California ѓе Alberta Clipper ЎV storm that moves quickly out of Canada in the winter Role of Mountains ѓе Mountains provide a barrier to the air in the troposphere ѓе Wind blowing over a mountain range finds its height shrinking due to the terrain below ѓе The shrinking of the air column causes divergence and the air to spin slowly (conservation of angular momentum) ѓе After passing the mountain range, the air column is stretched, resulting in convergence and the air to spin faster Appearance of a Mature Cyclone ѓе On a satellite picture, a mature cyclone can have the shape of a comma (Ўcomma cloudЎЁ) ѓе The tail of the comma is produced along the cold front ѓе The head of the comma is produced by clouds circling the low pressure ѓе The cloudless region between the head and tail is produced by dry air descending from aloft that causes evaporation (called the Ўdry slotЎЁ) Structure of Low Pressure ѓе Recall that the structure of low pressure has convergence at low levels, rising air above the center, and divergence aloft ѓе How can low pressure get even lower? ѓе The divergence aloft must be greater than the convergence at the surface Means of Divergence ѓе Divergence is the air moving apart ѓе This can happen in two ways: ЎV Speed divergence: Air speeding up downstream will cause the air parcels to spread out (like cars leaving a toll booth) ЎV Directional divergence: Air flowing away from each other will also cause air parcels to spread out (like two cars taking different paths at a Y-intersection) Anticyclones ѓе After the cold front of an extratropical cyclone, the next large weather system to appear is typically an anticyclone (high pressure) ѓе Lows form and grow along fronts (boundaries between air masses) ѓе Highs are the air masses themselves ѓе Lows ЎV short-lived, cloudy, wet, and stormy with strong pressure gradients ѓе Highs ЎV longer-lived, clear, dry, and calm with weak pressure gradients Anticyclone Characteristics ѓе Highs have divergence at the surface, with sinking air at the center and convergence aloft ѓе Sinking air is compressed and warmed ѓе As a result, the atmosphere is stable and a temperature inversion may exist aloft ѓе The inversion, along with typically weak winds, can combine to produce pollution episodes CLOUDS Cyclone Surface Ocean Currents The water at the ocean surface is moved primarily by winds that blow in certain patterns because of the Earths spin and the Coriolis Effect. Winds are able to move the top 400 meters of the ocean creating surface ocean currents. Surface ocean currents form large circular patterns called gyres. Gyres flow clockwise in Northern Hemisphere oceans and counterclockwise in Southern Hemisphere oceans because of the Coriolis Effect. creating surface ocean currents. Near the Earths poles, gyres tend to flow in the opposite direction. Surface ocean currents flow in a regular pattern, but they are not all the same. Some currents are deep and narrow. Other currents are shallow and wide. Currents are often affected by the shape of the ocean floor. Some move quickly while others move more slowly. A current can also change somewhat in depth and speed over time. Surface ocean currents can be very large. The Gulf Stream, a surface current in the North Atlantic, carries 4500 times more water than the Mississippi River. Each second, ninety million cubic meters of water is carried past Chesapeake Bay (US) in the Gulf Stream. Surface ocean currents carry heat from place to place in the Earth system. This affects regional climates. The Sun warms water at the equator more than it does at the high latitude polar regions. The heat travels in surface currents to higher latitudes. A current that brings warmth into a high latitude region will make that regions climate less chilly. Surface ocean currents can create eddies, swirling loops of water, as they flow. Surface ocean currents can also affect upwelling in many places. They are important for sailors planning routes through the ocean. Currents are also important for marine life because they transport creatures around the world and affect the water temperature in ecosystems. Motions of the Ocean Ocean water is always moving. Water swirls around ocean basins in surface ocean currents. The Gulf Stream is a surface current that runs between the United States and Europe in the North Atlantic Ocean. Smaller spinning rings of water called eddies can form from surface ocean currents. Ocean water also moves from the deep sea to the ocean surface. Places where this happens are called areas of upwelling. The marine life and the climate can be affected as the cold water makes its way up from the deep. The upwelling water is rich in nutrients so plankton flourishes, and it is very cold, which can lead to cool, damp and foggy weather. Moving water is found on smaller scales too. Waves travel across the ocean and crash on coastlines. Currents along coastlines have the power to transport sand to new places and to even move swimmers far from their beach towels. On a global scale, water moves each day with the tides. And over a long time it moves around the world from the shallow to deep oceans because of changes in the waters density - a process called thermohaline circulation. The moving water in the oceans transports heat and so it has a large impact on Earths climate. Thermohaline Circulation: The Global Ocean Conveyor The world has several oceans, the Pacific, the Atlantic, the Indian, the Arctic, and the Southern Ocean. While we have different names for them, they are not really separate. There are not walls between them. Water is able to move freely between oceans. They are all connected in one global ocean. If you visit a shoreline and watch the ocean, you will see water on the move. Waves crash on the beach. Tides move water back and forth twice a day, longshore currents and rip tides transport unobservant swimmers far away from their beach towels. These are some of the small scale ways that seawater moves. Seawater moves in larger ways too. There is a large-scale pattern to the way that seawater moves around the world ocean. This pattern is driven by changes in water temperature and salinity that change the density of water. It is known as the Global Ocean Conveyor or thermohaline circulation. It affects water at the ocean surface and all the way to the deep ocean. It moves water around the world. The Global Ocean Conveyor moves water slowly, 10 cm per second at most, but it moves a lot of water. One hundred times the amount of water that is in the Amazon River is being transported by this huge slow circulation pattern. The water moves mainly because of differences in relatively density. Water that is more dense sinks below water that is less dense. Two things affect the density of seawater: temperature and salinity. Cold water is denser than warm water. Water gets colder when it looses heat to the atmosphere, especially at high latitudes. Water gets warmer when it is heated by incoming solar energy, especially at low latitudes. Saltier water is denser than less salty water. Water gets saltier if rate of evaporation is high. Water gets less salty if there is an influx of freshwater either from melting ice or precipitation and runoff from land. In the Atlantic, the circulation of seawater is driven mainly by temperature differences right now. Water heated near the equator travels at the surface of the ocean north into high latitudes where it looses some heat to the atmosphere (keeping temperatures in Northern Europe and North America relatively mild). The cooled water sinks to the deep ocean and travels the world ocean, possibly not surfacing for hundreds or even as much as a thousand years. There is concern that as the Arctic warms and more sea ice melts, the influx of freshwater will make the seawater at high latitudes less dense. The less dense water will not be able to sink and circulate throughout the world. This may stop the global ocean conveyor and change the climate of the European and North American continents. Currents at the Coast Currents at the Coast global surface currents Ocean water circulates in currents caused by wind friction and by difference in the density of water masses beneath the surface zone Ocean current Ocean Surface Currents Oceanic gyre Great Pacific Garbage Patch Wind Driven Surface Currents: Gyres Background Ekman spiral (meteorology) A theoretical representation that a wind blowing steadily over an ocean of unlimited depth and extent and uniform viscosity would cause, in the Northern Hemisphere, the immediate surface water to drift at an angle of 45 to the right of the wind direction, and the water beneath to drift further to the right, and with slower and slower speeds, as one goes to greater depths The Ekman spiral, named after Swedish scientist Vagn Walfrid Ekman (1874-1954) who first theorized it in 1902, is a consequence of the Coriolis effect. When surface water molecules move by the force of the wind, they, in turn, drag deeper layers of water molecules below them. Each layer of water molecules is moved by friction from the shallower layer, and each deeper layer moves more slowly than the layer above it, until the movement ceases at a depth of about 100 meters (330 feet). Like the surface water, however, the deeper water is deflected by the Coriolis effectto the right in the Northern Hemisphere and to the left in the Southern Hemisphere. As a result, each successively deeper layer of water moves more slowly to the right or left, creating a spiral effect. Because the deeper layers of water move more slowly than the shallower layers, they tend to twist around and flow opposite to the surface current. Surface Ocean Currents Water near the ocean surface moves to the right of the wind direction in the Northern Hemisphere and to the lift in the Southern Hemisphere Geostrophic Gyres Geostrophic gyres are gyres in balance between the pressure gradient and the Coriolis effect. Of the six great currents in the worldнs ocean, five are geostrophic gyres Geostrophic Flow Dynamics Ocean Circulation I. Surface Currents a. About 10% of the oceans water is in surface currents, water flowing horizontally in the uppermost 400 m i. Driven mostly by wind friction ii. Most wind energy comes from the trade winds (easterlies) and westerlies iii. The moving water will pile up in the direction the wind is blowing 1. gravity will pull water down this slope, in the direction from which it came 2. However, the Coriolis effect causes surface currents in the N.Hemisphere to be deflected to the right and to the left in the S. Hemisphere. 3. Continents block the flow of the water, causing the currents to flow in large circular patterns called gyres. b. Gyres i. Example: N. Atlantic ii. Water flows clockwise around the N. Atlantic iii. The East/West winds flow to the right of the prevailing winds. iv. When driven by the wind, the topmost layer of the ocean in the N. Hemisphere flows at about 45 to the right of the wind direction. 1. Layers below the top layer respond by being deflected in a similar manner. 2. This trend continues to a depth of about 100 m below the surface 3. This results in an Ekman Spiral a. Ekman spirals transport water 90 to the right of wind in the N. Hemisphere and to the left in the S. Hemisphere b. They are about 100 m deep. 4. This causes a build up of water in the center of the ocean, which is really a hill of water about 2 m higher than the rest of the ocean. 5. This hill is maintained by wind energy, friction with the surrounding continents, and the coriolis effect. 6. Pressure gradients, from gravity, propel the currents of the gyre and hold them along the outside edges of the ocean basins. v. Geostrophic Gyres 1. Gyres in balance between the pressure gradient and the Coriolis effect are called geostrophic gyres (Geo=earth; strophe= turning), and their currents are called geostrophic currents. a. Geostrophic gyres are largely independent of each other. 2. There are six great current circuits in the world ocean. a. Two in the S. Hemisphere and four in the S. Hemisphere b. Five are Geostrophic gyres i. N. Atlantic ii. S. Atlantic iii. N. Pacific iv. S. Pacific v. Indian c. The sixth and largest current system is the Antarctic Circumpolar Current and because it flows around the entire world it is not considered geostrophic. vi. Currents within Gyres 1. Western Boundary Currents a. Located on the gyres western end b. Ex: Gulf Stream (G.S.), Kuroshio, Brazil, Agulhas, East Australian c. G.S. moves about 2 m/s (5 miles/h) off Miami i. Thats >160km/day ii. >450 m deep iii. Width about 70 km d. They transport warm water away from the equator e. Lots of water gets transported i. G.S. is at least 55 Sverdrups (sv), one sverdrup is 1 million cubic meters/second (about Ѕ the size of the Louisiana Superdome), about 300 times the flow of the Amazon f. Really looks like a river in the sea. i. The water is distinctly different. 1. Warmer 2. Clearer 3. Bluer ii. Often eddies, turbulent rings, form in the current and trap cold or warm water in the centers and then separate from the main stream 2. Eastern Boundary Currents a. There are five Eastern Boundary Currents i. Canary Current, ii. Benguela Current iii. California current iv. West Australian Current v. Humboldt or Peru current b. On the Eastern edge of the gyre. c. They carry cold water toward the equator d. They are shallow and broad e. They carry less water then W.B.C.s i. Canary current only carries about 16 svs 3. Transverse Currents a. These are currents that connect the E.B.C.s and W.B.C.s and are driven by winds b. The N. and S. Equatorial Currents in the Talantic and Pacific are formed by the push of the trade winds. c. These currents are usually impeded by continents. d. However, in the S. Ocean there are no continents in the way and the transverse current forms the Antarctic Circumpolar Current. 4. Countercurrents and Undercurrents a. Equitorial Currents are usually accompanied by countercurrents flowing on the surface in opposite direction of the main flow. b. This backward flow is a reaction to the build up of water on one side of the ocean. c. Countercurrents also exist beneath surface currents i. Called undercurrents, they are 100 to 200 m below the surface and can carry as much water as the surface currents. 5. Effect of currents on climate a. When you have warm water moving into colder regions it heats the atmosphere i. England is much warmer than Labrador, even though they are at comparable latitudes b. When you have cold water moving into warmer regions it cools the atmosphere i. Summers in Seattle are not as hot as summers in New York c. Upwelling and Downwelling i. In the Equatorial Pacific the trade winds cause the formation of the North and South Equitorial Currents 1. These currents move warm water across the pacific from the East to the West. a. In the East, along the coasts of Peru and Chile, the water removal of water causes coastal upwelling and the lowering of the sea surface height i. Upwelling: process by which deep, cold, nutrient-rich water is brought from depths to the surface ii. Coastal Upwelling : the movement of surface water away from a coast line causes deeper water to be brought up in order to replace it. iii. This deeper water is colder, because it is farther from the sun. iv. The sea surface is lower because 1. Water that removed 2. The water the replaces it is colder, denser and therefore has a smaller volume b. In the West, along the coasts of SE Asia and Micronesia, there is a build up of warm water. ii. During an El Niсo the trade winds weaken, stop all together, or even reverse direction. 1. This change in the winds caus es that pile of warm water in the Western Pacific to slosh back along the equator until it hits the South America a. The presence of that warm water creates a cap on the water column and effectively shuts down upwelling. b. Without the upwelling of nutrients, the productivity of the sea shuts down, thus destroying the fishery in Peru and Chile 2. During a strong El Niсo, the wave of warm equatorial water can be pushed along the coasts of North and South America, even as far north as Oregon. iii. When water is driven toward a coastline it will be forced downward returning seaward along the continental shelf 1. This downwelling supplies deeper ocean water with dissolved gases and nutrients d. Vertical Motion and the Three-Layered Ocean i. The oceans are a three dimensional habitat and vary horizontally and vertically. 1. Many of the changes in habitat are due to changes with depth. 2. The three-dimensional structure of water is a function of its density 3. That is why oceanographers measure the temperature and salinity of the water column. ii. Because the densest water sinks, the ocean is often layered, or stratified. 1. The surface water tends to stay where it is and float on the denser water below, so the water column is said to be stable, that is it is difficult to mix the layers. 2. How stable the water is depends on the differences in density between the surface and the deep water. iii. Occasionally, surface water becomes more dense than the water below it. 1. The surface water sinks, displacing the less dense water below in a process known as overturn. 2. This occurs when the density remains constant with depth. 3. Water will descend to the depth determined by its density. iv. The processes that change salinity in the open ocean, evaporation, precipitation and freezing, only occur at the surface, and the largest changes in temperature also occur mainly at the surface. 1. Therefore, once surface water has sunk, it is imprinted with a characteristic temperature and salinity. 2. Oceanographers use this to follow the movement, or circulation, of water masses over great distances, known as thermohaline circulation. II. Thermohaline Circulation a. Thermohaline (thermo=temperature, haline=salt) circulation is the movement of water due to its density i. Responsible for the majority of non-surface water movement in the oceans, both vertical and horizontal b. Three-Layered Ocean i. Surface Layer 100-200 m thick 1. Much of it is mixed by wind, waves and currents, so its known as the mixed layer. 2. There often exists a seasonal thermocline, or region of rapid temperature change, in this layer ii. Intermediate Layer- from 200m to 1,500m 1. Characterized by the permanent thermocline , the zone of transition between warm surface water and the cold water below. 2. Do not confuse with seasonal thermocline. 3. The permanent thermocline rarely breaks down and is a feature of the deep ocean, not of shelf regions. iii. Deep and Bottom Layers- below 1500m 1. Technically these are two different kinds of water but they are both uniformly cold at about 4C. c. T/S Diagrams i. Temperature/Salinity Diagrams (T/S Diagrams) are used to describe different water masses. 1. Note that many combinations of temperature and salinity can yield the same density d. Formation and Downwelling of Deep water i. Antarctic Bottom Water, the most distinctive of all water masses 1. Formed in the Weddell Sea when ice freezes, extruding salt and making very cold, very salty water ii. Other Deep water formation 1. North Atlantic Deep Water is formed when the relatively warm and salty N. Atlantic cools and sinks between Iceland and Greenland 2. Some dense deep water forms in the Arctic Ocean, but the bottom topography prevents most of it from escaping, except in a few places near Scotland, Iceland and Greenland e. Thermohaline Circulation Patterns i. This sinking water must be balanced by rising water ii. The continual diffuse upwelling of deep water maintains the existence of the permanent thermocline found everywhere at low and mid- latitudes. 1. This slow upward movement is estimated to be about 1 cm/ per day over most of the ocean iii. Water masses butt against each other in convergence zones and the heavier water can slide beneath the lighter water f. Thermohaline Flow and Surface Flow: The Global Heat Connection i. The transport of tropical water to the polar regions is part of The Great Conveyor Belt for heat. 1. The slow, steady three-dimensional flow of water in the conveyor belt distributes dissolved gases and solids, mixes nutrients and transports the juvenile stages of organisms between ocean basins. Surface Ocean Geostrophic flow Gyre currents Westward intensification Upwelling, downwelling, and Ekman pumping Antarctic circumpolar current http://oceancurrents.rsmas.miami.edu/southern/antarctic-cp.html http://www.parks.tas.gov.au/fahan_mi_shipwrecks/infohut/acc.htm Deep Circulation in the Ocean Cures within Gyres Boundary current Western Boundary Currents: Gulf Stream, Kuroshio Current Western and Eastern Boundary Currents Gulf Stream Sverdrup The sverdrup, named in honour of the pioneering oceanographer Harald Sverdrup, is a unit of measure of volume transport. It is used almost exclusively in oceanography, to measure the transport of ocean currents. Its symbol is Sv. Note that the sverdrup is not an SI unit, and that its symbol conflicts with the sievert''s. It is equivalent to 106 cubic meters per second (0.001 kmі/s, or about 264 million U.S. gallons per second). Rings in the Ocean Turbulent rings = Eddies rings Eddy (fluid dynamics) Warm-core eddies in the Gulf of Mexico eddies Guilf Stream Dynamics Effects of electromagnetic influences in nature: Oceanic Currents WESTWARD INTENSIFICATION OF A CURRENT The Coriolis effect modifies the courses of currents, with currents turning clockwise in the Northern Hemisphere and counterclockwise in the S. Hemisphere. The Coriolis effect is largely responsible for the phenomenon of westward intensification in both hemispheres. HOW DO WE MEASURE CURRENTS Ocean Currents and Climate Ocean circulation affects climate and plant and animal populations on land and in the ocean Upwelling Upwelling-video In this animation, winds blowing along the coast push the coastal surface water. When combined with the Coriolis effect, this motion moves surface water away from the coast. As surface water moves outward, cold, plankton-rich water from the ocean bottom moves toward the coast and rises to replace the displaced surface water. Upwelling upwelling and downwelling Upwelling and downwelling describe the vertical movement of water masses. Upwelling is often due to the divergence of surface currents; downwelling is often caused by surface current convergence or an increase in the density of surface water Equatorial upwelling Equatorial upwelling Coastal Upwelling and California El Nino, an anomaly in surface circulation, occurs when the trade winds falter, allowing warm water to build eastward across the Pacific at the equator. Coastal upwelling and Ekman transport http://www.atmos.washington.edu/gcg/RTN/Figures/RTN13.html El Nio-Southern Oscillation Thermohaline circulation Circulation of the 90% of ocean water beneath the surface zone is driven by the force of gravity, as dence water sinks and less dense water rises. Because density is largely a function of temperature and salinity, the movement of deep water due to density difference is called termohaline circulation. Water masses Surface water Central water Intermediate water Deep water Bottom water Water masses almost always form at the ocean surface. The densest (and deepest) masses were formed by surface conditions that caused water to become very cold and salty. Antarctic Bottom Water North Atlantic deep water Thermohaline Circulation Patterns Convergence zones Thermohaline flow and surface flow The global heat connection Because they transfer huge quantities of heat, ocean currents greatly affect world weather and climate Studying currents |
