DOCSLIB.ORG

Lecture 4: OCEANS (Outline)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Lecture 4: OCEANS (Outline) Lecture 4 : OCEANS (Outline) Basic Ocean Structures Warm up by sunlight! Basic Structures and Dynamics Upper Ocean (~100 m) Ekman transport Geostrophic currents Shallow, warm upper layer where light is Surface Ocean Circulation abundant and where most marine life can be found. Subtropicl gyre Boundary current Deep Ocean Deep Ocean Circulation Cold, dark, deep ocean where plenty supplies of Thermohaline conveyor belt nutrients and carbon exist. ESS200A ESS200A Prof. Jin-Yi Yu No sunlight! Prof. Jin-Yi Yu Basic Ocean Current Systems The State of Oceans Upper Ocean surface Temperature circulation warm on the upper ocean, cold in the deeper ocean. Salinity variations determined by evaporation, precipitation, Deep Ocean sea-ice formation and melt, and river runoff. Density deep ocean circulation small in the upper ocean, large in the deeper ocean. ESS200A ESS200A (from “Is The Temperature Rising?”) Prof. Jin-Yi Yu Prof. Jin-Yi Yu 1 Salinity E < P Sea-ice formation and melting Potential Temperature E > P Potential temperature is Salinity is the mass of very close to temperature in dissolved salts in a the ocean. kilogram of seawater. The average temperature Unit: ‰ (part per of the world ocean is about thousand; per mil). 3.6°C. The average salinity of the world ocean is 34.7‰. Four major factors that affect salinity: evaporation, precipitation, inflow of river water, and sea-ice formation and melting. ESS200A (from Global Physical Climatology ) ESS200A (from Global Physical Climatology ) Prof. Jin-Yi Yu Prof. Jin-Yi Yu Low density due to absorption of solar energy near the surface. Density and Temperature and Salinity Density Seawater is almost incompressible, so the density of seawater is always very close to 1000 kg/m 3. Potential density is the density that seawater with a particular salinity and temperature would have at zero water pressure (or at surface air pressure). Potential density = density – 1000 kg/m 3. (from Global Physical Climatology ) ESS200A ESS200A Prof. Jin-Yi Yu (Figure from Oceanography by Tom Garrison) Prof. Jin-Yi Yu 2 Vertical Structure of Ocean Mixed Layer Processes The depth of the mixed layer is determined by (1) the rate of Mixed Layer: T and S well mixed by winds buoyancy generation and (2) the rate of kinetic energy supply. Temperature Thermocline: large gradient of T and S The atmosphere can affect the Salinity mixed layer through three Deep Ocean: T and S independent of height processes: heating, wind forcing, cold and freshening (P-E). salty The global-average depth of high nutrient level the mixed layer is about 70 m. The heat capacity of the mixed layer is about 30 times the heat (from Global Physical Climatology ) capacity of the atmosphere. (from Climate System Modeling ) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Seasonal Variation of Mixed Layer Two Circulation Systems Summer: warm and thin. Winter: cold and deep (several hundred meters). density-driven wind-driven circulation (from Global Physical Climatology ) (Figure from The Earth System ) circulation ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu 3 Global Surface Currents Six Great Current Circuits in the World Ocean 5 of them are geostrophic gyres: North Pacific Gyre South Pacific Gyre North Atlantic Gyre South Atlantic Gyre Indian Ocean Gyre The 6 th and the largest current: Antarctic Circumpolr Current (also called West Wind Drift) (Figure from Oceanography by Tom Garrison) (from Climate System Modeling ) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Characteristics of the Gyres Major Current Names (Figure from Oceanography by Tom Garrison) Currents are in geostropic balance Each gyre includes 4 current components: Western Boundary Current Trade Wind-Driven Current two boundary currents: western and eastern Gulf Stream (in the North Atlantic) North Equatorial Current two transverse currents: easteward and westward Kuroshio Current (in the North Pacific) South Equatorial Current Western boundary current (jet stream of ocean) Brazil Current (in the South Atlantic) the fast, deep, and narrow current moves warm Eastern Australian Current (in the South Pacific) water polarward (transport ~50 Sv or greater) Agulhas Current (in the Indian Ocean) Eastern boundary current the slow, shallow, and broad current moves cold water equatorward (transport ~ 10-15 Sv) Eastern Boundary Current Westerly-Driven Current Trade wind-driven current Canary Current (in the North Atlantic) North Atlantic Current (in the North Atlantic) the moderately shallow and broad westward California Current (in the North Pacific) North Pacific Current (in the North Pacific) current (transport ~ 30 Sv) Benguela Current (in the South Atlantic) Westerly-driven current Peru Current (in the South Pacific) Western Australian Current (in the Indian Ocean) the wider and slower (than the trade wind-driven Volume transport unit: current) eastward current 1 sv = 1 Sverdrup = 1 million m 3/sec ESS200A ESS200A (the Amazon river has a transport of ~0.17 Sv) Prof. Jin-Yi Yu Prof. Jin-Yi Yu 4 Gulf Stream Surface Current – Geostrophic Gyre A river of current Mixed Layer Jet stream in the ocean Currents controlled by frictional force + Coriolis force wind-driven circulation Ekman transport (horizontal direction) convergence/divergence downwelling/upwelling at the bottom of mixed layer Speed = 2 m/sec Depth = 450 m Thermocline Width = 70 Km downwelling/upwelling in the mixed layer Color: clear and blue pressure gradient force + Coriolis force geostrophic current Sverdrup transport (horizontal) (Figure from Oceanography by Tom Garrison) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Step 1: Surface Winds Winds and Surface Currents Polar Cell Ferrel Cell Hadley Cell (Figure from The Earth System ) (Figure from Oceanography by Tom Garrison) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu 5 Step 2: Ekman Layer Ekman Spiral – A Result of Coriolis Force (frictional force + Coriolis Force) (Figure from Oceanography by Tom Garrison) ESS200A (Figure from The Earth System ) ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Formula for Ekman Transport How Deep is the Ekman Layer? D ∝ (ν/f)1/2 ν = vertical diffusivity of momentum f = Coriolis parameter = 2 Ωsin φ ESS200A (from Climate System Modeling ) ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu 6 Step 3: Geostrophic Current Ekman Transport (Pressure Gradient Force + Corioils Foce) NASA-TOPEX Observations of Sea-Level Hight (from Oceanography by Tom Garrison) (Figure from The Earth System ) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Ekman Transport Convergence/Divergence Geostrophic Current (Figure from The Earth System ) Surface wind + Coriolis Force Ekman Transport Forces Geostrophic Gyre Currents Convergence/divergence Thermocline (in the center of the gyre) Pressure Gradient Force Geostrophic Currents (Figure from The Earth System ) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu 7 Step 4: Boundary Currents Boundary Currents Eastern boundary currents: broad and weak (Figure from Oceanography by Tom Garrison) ESS200A Western boundary currents: narrow and strong ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Eastern Boundary Current Costal Upwelling/Downwelling Cold water from higher latitude ocean. Costal upwelling associated with subtropical A result of Ekman high pressure system. transport and mass Atmospheric subsidence continuity. produce persistent stratiform clouds, which further cool down SSTs by blocking (from Global Physical Climatology ) solar radiation. (Figure from Oceanography by Tom Garrison) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu 8 Global Surface Currents Equatorial Current System The Equatorial Counter Current , which flows towards the east, is a partial return of water carried westward by the North and South Equatorial currents. ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Equatorial Under Current Deep Ocean Circulation: Density-Driven The most prominent of all eastward flows is the Equatorial Undercurrent (EUC). It is a swift flowing ribbon of water extending over a distance of more than 14,000 km along the equator with a thickness of only 200 m and a width of at most 400 km. The current core is found at 200 m depth in the west, rises to 40 m or less in the east and shows typical speeds of up to 1.5 m s-1. Its existence remained unknown to oceanographers until 1952. ESS200A ESS200A Prof. Jin-Yi Yu (Figure from Oceanography by Tom Garrison) Prof. Jin-Yi Yu 9 Thermohaline Circulation Two Regions of Deep Water Formation Antarctic Bottom Water Salinity = 34.65‰ Temperature = -0.5°C Density = 1.0279 g/cm 3 Formed at Weddell Sea Related to ice formation During Winter North Atlantic Deep Water Due to winter cooling and evaporation. (Figure from Oceanography by Tom Garrison) (Figure from Oceanography by Tom Garrison) ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu Two Processes to Increase Ocean Water Mass Salinity in High Latitudes Surface Water to a depth of about 200 meters • Ocean water masses possess distinct, identifiable properties Central Water and don’t often mix easily Evaporation : Extremely cold, dry winter when they meet. to the bottom of the main thermocline air enhances evaporation from the relatively • In stead, they usually flow warm ocean increase salinity in the Intermediate Water above or below each other. to about 1500 meters • Ocean water mass can retain ocean. their identity for great distance Deep Water and long periods of time. Formation of Sea Ice : When sea ice forms, below intermediate water but not in • Oceanographers name water contact with the bottom masses according to their salts are left in the ocean increase relative position. salinity Bottom Water in contact with sea floor ESS200A ESS200A Prof. Jin-Yi Yu Prof. Jin-Yi Yu 10 Five Types of Air Masses Formation of Water Mass Theoretically, there should be 6 types of air masses (2 moisture Once a water parcel is removed from the surface layer its temperature and salinity do not change until it rises back up to the surface again, types x 3 temperature types).
Load more

Recommended publications
  • Fronts in the World Ocean's Large Marine Ecosystems. ICES CM 2007
    - 1 - This paper can be freely cited without prior reference to the authors International Council ICES CM 2007/D:21 for the Exploration Theme Session D: Comparative Marine Ecosystem of the Sea (ICES) Structure and Function: Descriptors and Characteristics Fronts in the World Ocean’s Large Marine Ecosystems Igor M. Belkin and Peter C. Cornillon Abstract. Oceanic fronts shape marine ecosystems; therefore front mapping and characterization is one of the most important aspects of physical oceanography. Here we report on the first effort to map and describe all major fronts in the World Ocean’s Large Marine Ecosystems (LMEs). Apart from a geographical review, these fronts are classified according to their origin and physical mechanisms that maintain them. This first-ever zero-order pattern of the LME fronts is based on a unique global frontal data base assembled at the University of Rhode Island. Thermal fronts were automatically derived from 12 years (1985-1996) of twice-daily satellite 9-km resolution global AVHRR SST fields with the Cayula-Cornillon front detection algorithm. These frontal maps serve as guidance in using hydrographic data to explore subsurface thermohaline fronts, whose surface thermal signatures have been mapped from space. Our most recent study of chlorophyll fronts in the Northwest Atlantic from high-resolution 1-km data (Belkin and O’Reilly, 2007) revealed a close spatial association between chlorophyll fronts and SST fronts, suggesting causative links between these two types of fronts. Keywords: Fronts; Large Marine Ecosystems; World Ocean; sea surface temperature. Igor M. Belkin: Graduate School of Oceanography, University of Rhode Island, 215 South Ferry Road, Narragansett, Rhode Island 02882, USA [tel.: +1 401 874 6533, fax: +1 874 6728, email: [email protected]].
    [Show full text]
  • The Gulf Stream (Western Boundary Current)
    Classic CZCS Scenes Chapter 6: The Gulf Stream (Western Boundary Current) The Caribbean Sea and the Gulf of Mexico are the source of what is likely the most well- known current in the oceans—the Gulf Stream. The warm waters of the Gulf Stream can be observed using several different types of remote sensors, including sensors of ocean color (CZCS), sea surface temperature, and altimetry. Images of the Gulf Stream taken by the CZCS, one of which is shown here, are both striking and familiar. CZCS image of the Gulf Stream and northeastern coast of the United States. Several large Gulf Stream warm core rings are visible in this image, as are higher productivity areas near the Chesapeake and Delaware Bays. To the northeast, part of the Grand Banks region near Nova Scotia is visible. Despite the high productivity of this region, overfishing caused the total collapse of the Grand Banks cod fishery in the early 1990s. The Gulf Stream is a western boundary current, indicating that if flows along the west side of a major ocean basin (in this case the North Atlantic Ocean). The corresponding current in the Pacific Ocean is called the Kuroshio, which flows north to about the center of the Japanese archipelago and then turns eastward into the central Pacific basin. In the Southern Hemisphere, the most noteworthy western boundary current is the Agulhas Current in the Indian Ocean. Note that the Agulhas flows southward instead of northward like the Gulf Stream and the Kuroshio. Western boundary currents result from the interaction of ocean basin topography, the general direction of the prevailing winds, and the general motion of oceanic waters induced by Earth's rotation.
    [Show full text]
  • Physical Oceanography - UNAM, Mexico Lecture 3: the Wind-Driven Oceanic Circulation
    Physical Oceanography - UNAM, Mexico Lecture 3: The Wind-Driven Oceanic Circulation Robin Waldman October 17th 2018 A first taste... Many large-scale circulation features are wind-forced ! Outline The Ekman currents and Sverdrup balance The western intensification of gyres The Southern Ocean circulation The Tropical circulation Outline The Ekman currents and Sverdrup balance The western intensification of gyres The Southern Ocean circulation The Tropical circulation Ekman currents Introduction : I First quantitative theory relating the winds and ocean circulation. I Can be deduced by applying a dimensional analysis to the horizontal momentum equations within the surface layer. The resulting balance is geostrophic plus Ekman : I geostrophic : Coriolis and pressure force I Ekman : Coriolis and vertical turbulent momentum fluxes modelled as diffusivities. Ekman currents Ekman’s hypotheses : I The ocean is infinitely large and wide, so that interactions with topography can be neglected ; ¶uh I It has reached a steady state, so that the Eulerian derivative ¶t = 0 ; I It is homogeneous horizontally, so that (uh:r)uh = 0, ¶uh rh:(khurh)uh = 0 and by continuity w = 0 hence w ¶z = 0 ; I Its density is constant, which has the same consequence as the Boussinesq hypotheses for the horizontal momentum equations ; I The vertical eddy diffusivity kzu is constant. ¶ 2u f k × u = k E E zu ¶z2 that is : k ¶ 2v u = zu E E f ¶z2 k ¶ 2u v = − zu E E f ¶z2 Ekman currents Ekman balance : k ¶ 2v u = zu E E f ¶z2 k ¶ 2u v = − zu E E f ¶z2 Ekman currents Ekman balance : ¶ 2u f k × u = k E E zu ¶z2 that is : Ekman currents Ekman balance : ¶ 2u f k × u = k E E zu ¶z2 that is : k ¶ 2v u = zu E E f ¶z2 k ¶ 2u v = − zu E E f ¶z2 ¶uh τ = r0kzu ¶z 0 with τ the surface wind stress.
    [Show full text]
  • Responses of Eastern Boundary Current Ecosystems to Anthropogenic Climate Change
    Responses of Eastern Boundary Current Ecosystems to Anthropogenic Climate Change 1900 2100 Ryan R. Rykaczewski University of South Carolina ryk @ sc.edu We are united by an interest in understanding ecosystem dynamics in the North Pacific Tokyo Columbia ~35,000 students (~300 students in Marine Sciences, with 13 faculty members) John Steven Julia me Riley Viki Connor Sarah Brian Tricia Q: What sorts of scientific topics do we study in my group? A: We want to understand why abundances of fish go up and down. Why is it that fish populations are so abundant (and lucrative to exploit!) during some years and absent during others? How do changes in large-scale physical processes influence… …the structure of the marine ecosystems—species composition and size distribution of the plankton, inter and intra-specific interactions, trophic transfer efficiency… …and affect the world’s marine fish stocks? Variability in eastern boundary current upwelling systems California Canary Current Current Humboldt Benguela Current Current Variability in eastern boundary current upwelling systems oceanic high continental pressure low pressure understand the dynamics of Long-term goal: upwelling ecosystems Upwelling systems: - support highly productive food webs and sustain fisheries critical to the world’s food supply. - may play a role in large-scale climate processes. Major genera include Sardinops and Engraulis inhabiting each of the four major eastern boundary currents. The Kuroshio stands out as the non- eastern boundary current with major stocks of sardine (Sardinops melanostictis) and anchovy (Engraulis japonicas). Many hypotheses relate fisheries fluctuations to physics What drives past changes Landings in the US state of California in fish abundance? Overfishing? Environmental variability? How? Why? Warm Conditions Cold Conditions Soutar and Isaacs (1969); Baumgartner et al.
    [Show full text]
  • Tidally Modified Western Boundary Current Drives Interbasin Exchange
    www.nature.com/scientificreports OPEN Tidally modifed western boundary current drives interbasin exchange between the Sea of Okhotsk and the North Pacifc Hung‑Wei Shu1,2*, Humio Mitsudera1, Kaihe Yamazaki2,3, Tomohiro Nakamura1, Takao Kawasaki4, Takuya Nakanowatari5, Hatsumi Nishikawa1,4 & Hideharu Sasaki6 The interbasin exchange between the Sea of Okhotsk and the North Pacifc governs the intermediate water ventilation and fertilization of the nutrient‑rich subpolar Pacifc, and thus has an enormous infuence on the North Pacifc. However, the mechanism of this exchange is puzzling; current studies have not explained how the western boundary current (WBC) of the subarctic North Pacifc intrudes only partially into the Sea of Okhotsk. High‑resolution models often exhibit unrealistically small exchanges, as the WBC overshoots passing by deep straits and does not induce exchange fows. Therefore, partial intrusion cannot be solely explained by large‑scale, wind‑driven circulation. Here, we demonstrate that tidal forcing is the missing mechanism that drives the exchange by steering the WBC pathway. Upstream of the deep straits, tidally‑generated topographically trapped waves over a bank lead to cross‑slope upwelling. This upwelling enhances bottom pressure, thereby steering the WBC pathway toward the deep straits. The upwelling is identifed as the source of joint‑efect‑of‑ baroclinicity‑and‑relief (JEBAR) in the potential vorticity equation, which is caused by tidal oscillation instead of tidally‑enhanced vertical mixing. The WBC then hits the island chain and induces exchange fows. This tidal control of WBC pathways is applicable on subpolar and polar regions globally. Te water exchange between the Sea of Okhotsk and the North Pacifc is an essential component of the over- turning circulation that ventilates the intermediate layer of the North Pacifc 1.
    [Show full text]
  • Ocean-Gyre-4.Pdf
    This website would like to remind you: Your browser (Apple Safari 4) is out of date. Update your browser for more × security, comfort and the best experience on this site. Encyclopedic Entry ocean gyre For the complete encyclopedic entry with media resources, visit: http://education.nationalgeographic.com/encyclopedia/ocean-gyre/ An ocean gyre is a large system of circular ocean currents formed by global wind patterns and forces created by Earth’s rotation. The movement of the world’s major ocean gyres helps drive the “ocean conveyor belt.” The ocean conveyor belt circulates ocean water around the entire planet. Also known as thermohaline circulation, the ocean conveyor belt is essential for regulating temperature, salinity and nutrient flow throughout the ocean. How a Gyre Forms Three forces cause the circulation of a gyre: global wind patterns, Earth’s rotation, and Earth’s landmasses. Wind drags on the ocean surface, causing water to move in the direction the wind is blowing. The Earth’s rotation deflects, or changes the direction of, these wind-driven currents. This deflection is a part of the Coriolis effect. The Coriolis effect shifts surface currents by angles of about 45 degrees. In the Northern Hemisphere, ocean currents are deflected to the right, in a clockwise motion. In the Southern Hemisphere, ocean currents are pushed to the left, in a counterclockwise motion. Beneath surface currents of the gyre, the Coriolis effect results in what is called an Ekman spiral. While surface currents are deflected by about 45 degrees, each deeper layer in the water column is deflected slightly less.
    [Show full text]
  • Three-Dimensional Model-Observation Intercomparison
    Dynamics of Atmospheres and Oceans 76 (2016) 283–305 Contents lists available at ScienceDirect Dynamics of Atmospheres and Oceans journal homepage: www.elsevier.com/locate/dynatmoce Three-dimensional model-observation comparison in the Loop Current region a,∗ a b K.C. Rosburg , K.A. Donohue , E.P. Chassignet a Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, USA b Center for Ocean-Atmosphere Prediction Studies, Florida State University, Tallahassee, FL, USA a r t i c l e i n f o a b s t r a c t Article history: Accurate high-resolution ocean models are required for hurricane and oil spill pathway pre- Received 9 October 2015 dictions, and to enhance the dynamical understanding of circulation dynamics. Output from Received in revised form 4 May 2016 ◦ the 1/25 data-assimilating Gulf of Mexico HYbrid Coordinate Ocean Model (HYCOM31.0) Accepted 4 May 2016 is compared to daily full water column observations from a moored array, with a focus on Available online 6 May 2016 Loop Current path variability and upper-deep layer coupling during eddy separation. Array- mean correlation was 0.93 for sea surface height, and 0.93, 0.63, and 0.75 in the thermocline Keywords: for temperature, zonal, and meridional velocity, respectively. Peaks in modeled eddy kinetic Evaluation energy were consistent with observations during Loop Current eddy separation, but with Modelling modeled deep eddy kinetic energy at half the observed amplitude. Modeled and observed Ocean currents LC meander phase speeds agreed within 8% and 2% of each other within the 100 – 40 and 40 Mesoscale eddies Baroclinic instability – 20 day bands, respectively.
    [Show full text]
  • OSTST Abstracts
    2015 Ocean Surface Topography Science Team Meeting Tuesday, October 20 2015 - Friday, October 23 2015 The objectives of the 2015 OSTST Meeting will be: (1) provide updates on the status of Jason-2 (2) conduct splinter meetings on system performance (orbit, measurements, corrections), altimetry data products, science outcomes, and outreach In addition to the traditional in-depth analyses of TOPEX/Poseidon-Jason missions, analyses from other missions bringing reciprocal benefits are welcome. Abstracts Book 1 / 219 Abstract list 2 / 219 Keynote/invited OSTST Opening Plenary Session Tue, Oct 20 2015, 09:00 - 12:30 - Grand Ballroom 1 11:00 - 11:20: What Do We Really Know About 20th Century Global Mean Sea Level?: Benjamin Hamlington et al. 11:20 - 11:40: AlborEx: a multi-platform interdisciplinary view of Meso and Submesoscale processes: Ananda Pascual et al. 11:40 - 12:00: Explaining the spread in global mean thermosteric sea level rise in CMIP5 climate models: Angelique Melet et al. Oral Application development for Operations (previously NRT splinter) Wed, Oct 21 2015, 09:00 - 10:30 - Grand Ballroom 2 09:00 - 09:15: Are SAR wave spectra from Sentinel-1A ready for operational use in the wave model MFWAM: Lotfi Aouf et al. 09:15 - 09:30: Improved Representation of Eddies in Fine Resolution Forecasting Systems Using Multi-Scale Data Assimilation of Satellite Altimetry: Zhijin Li 09:30 - 09:45: NOAA Operational Satellite Derived Oceanic Heat Content Products : Eileen Maturi et al. 09:45 - 10:00: On the use of recent altimeter products in NCEP ocean forecast system for the Atlantic (RTOFS Atlantic): Liyan Liu et al.
    [Show full text]
  • 0 Ekman Transport and Ekman Pumping in a Typical Ocean Basin
    Lecture 8 Lecture 1 Wind-driven gyres Ekman transport and Ekman pumping in a typical ocean basin. VEk wEk > 0 VEk wEk < 0 VEk 1 8.1 Vorticity and circulation The vorticity of a parcel is a measure of its spin about its axis. Imagine a closed contour encircling an dl ocean eddy. We define the circulation around the contour as u By convention, an anticlockwise circulation is defined as positive. e.g. for a cylindrically symmetric eddy, the circulation around a r streamline at radius r is: u e.g. consider a rectangular path in a fluid whose velocity varies spatially. The circulation is: Note that C depends on the size of the path. It is therefore useful to define the vorticity (ξ) as the circulation per unit area: Where flow fields are continuous: 2 Vorticity is directly related to the horizontal shear of a flow field: × × y x 8.2 Kelvin’s Circulation Theorem In the absence of viscosity and density variations, the circulation is conserved following a fluid parcel. This means we can think of vortex tubes: e.g. smoke rings are advected by the flow, conserving their circulation. 3 Divergence of the flow in a direction parallel to the axis of spin leads to an increase in the vorticity: ξfinal h0 hfinal ξ0 Stretching → vorticity increase The bath plug vortex - water columns are stretched as they exit through the plug hole, increasing their vorticity! Does this have anything to do with which hemisphere you are in?! 4 8.3 Absolute vorticity The planet’s rotation also introduces local spin.
    [Show full text]
  • Physical Climate Processes and Feedbacks
    7 Physical Climate Processes and Feedbacks Co-ordinating Lead Author T.F. Stocker Lead Authors G.K.C. Clarke, H. Le Treut, R.S. Lindzen, V.P. Meleshko, R.K. Mugara, T.N. Palmer, R.T. Pierrehumbert, P.J. Sellers, K.E. Trenberth, J. Willebrand Contributing Authors R.B. Alley, O.E. Anisimov, C. Appenzeller, R.G. Barry, J.J. Bates, R. Bindschadler, G.B. Bonan, C.W. Böning, S. Bony, H. Bryden, M.A. Cane, J.A. Curry, T. Delworth, A.S. Denning, R.E. Dickinson, K. Echelmeyer, K. Emanuel, G. Flato, I. Fung, M. Geller, P.R. Gent, S.M. Griffies, I. Held, A. Henderson-Sellers, A.A.M. Holtslag, F. Hourdin, J.W. Hurrell, V.M. Kattsov, P.D. Killworth, Y. Kushnir, W.G. Large, M. Latif, P. Lemke, M.E. Mann, G. Meehl, U. Mikolajewicz, W. O’Hirok, C.L. Parkinson, A. Payne, A. Pitman, J. Polcher, I. Polyakov, V. Ramaswamy, P.J. Rasch, E.P. Salathe, C. Schär, R.W. Schmitt, T.G. Shepherd, B.J. Soden, R.W. Spencer, P. Taylor, A. Timmermann, K.Y. Vinnikov, M. Visbeck, S.E. Wijffels, M. Wild Review Editors S. Manabe, P. Mason Contents Executive Summary 419 7.3 Oceanic Processes and Feedbacks 435 7.3.1 Surface Mixed Layer 436 7.1 Introduction 421 7.3.2 Convection 436 7.1.1 Issues of Continuing Interest 421 7.3.3 Interior Ocean Mixing 437 7.1.2 New Results since the SAR 422 7.3.4 Mesoscale Eddies 437 7.1.3 Predictability of the Climate System 422 7.3.5 Flows over Sills and through Straits 438 7.3.6 Horizontal Circulation and Boundary 7.2 Atmospheric Processes and Feedbacks 423 Currents 439 7.2.1 Physics of the Water Vapour and Cloud 7.3.7 Thermohaline Circulation
    [Show full text]
  • Ocean Circulation: the Planet’S Great Heat Engine
    NIWA WATER & ATMOSPHERE 9(4) 2001 LESSONS OF THE PAST Ocean circulation: the planet’s great heat engine Barbara THE OCEAN is in perpetual motion: that’s The Pacific gateway Manighetti obvious to anyone who looks out over the sea. Today, 40% of the densest deep water enters But the tides and waves that we see are just a the world’s ocean via the southwest Pacific, tiny part of the movement in the ocean as a and New Zealand is at the gateway of this huge Giant currents in whole. Most movement comprises large-scale, flow. unseen shifts to equal out water density the deep ocean The Deep Western Boundary Current of the differences caused by variations in temperature southwest Pacific travels 2–5 km below the transport so much and salinity (saltiness) from the Poles to the surface along the east side of the Campbell Tropics. Dense water (i.e., cold and salty) tends heat around the Plateau, around Chatham Rise and around to sink and then flow sideways at its appropriate globe that they Hikurangi Plateau (see inset map, below right). density level, generating currents that flow On its journey past New Zealand, the boundary play a critical role from basin to basin, redistributing heat and salt current helps to redistribute heat, salt and as they go. This is called thermohaline in shaping the nutrients. To compensate for this northward circulation. earth’s climate. flow of deep water, there is a southward Cold, salty deep water is produced in the seas movement of shallower water in the upper around Antarctica and the high North Atlantic.
    [Show full text]
  • An Introduction to the Oceanography, Geology, Biogeography, and Fisheries of the Tropical and Subtropical Western Central Atlantic
    click for previous page Introduction 1 An Introduction to the Oceanography, Geology, Biogeography, and Fisheries of the Tropical and Subtropical Western Central Atlantic M.L. Smith, Center for Applied Biodiversity Science, Conservation International, Washington, DC, USA, K.E. Carpenter, Department of Biological Sciences, Old Dominion University, Norfolk, Virginia, USA, R.W. Waller, Center for Applied Biodiversity Science, Conservation International, Washington, DC, USA his identification guide focuses on marine spe- lithospheric units, deep ocean basins separated Tcies occurring in the Western Central Atlantic by relatively shallow sills, and extensive systems Ocean including the Gulf of Mexico and Caribbean of island platforms, offshore banks, and Sea; these waters collectively comprise FAO Fishing continental shelves (Figs 2,3). One consequence Area 31 (Fig. 1). The western parts of this area have of this geography is a fine-grained pattern of often been referred to as the “wider Caribbean Basin” biological diversification that adds up to the or, more recently, as the Intra-Americas Sea (e.g., greatest concentration of rare and endemic Mooers and Maul, 1998). The latter term draws atten- species in the Atlantic Ocean Basin. Of the 987 tion to the fact that marine waters lie at the heart of the fish species treated in detail in these volumes, Americas and that they constitute an American Medi- some 23% are rare or endemic to the study area. terranean that has played a key geopolitical role in the Such a high level of endemism stands in contrast development of the surrounding societies. to the widespread view that marine species characteristically have large geographic ranges In geographic terms, the Western Central and that they might therefore be buffered against Atlantic (WCA) is one of the most complex parts of the extinction.
    [Show full text]