Eddy-Mean-Flow Interaction in a Barotropic Ocean Model
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A Global Ocean Wind Stress Climatology Based on Ecmwf Analyses
NCAR/TN-338+STR NCAR TECHNICAL NOTE - August 1989 A GLOBAL OCEAN WIND STRESS CLIMATOLOGY BASED ON ECMWF ANALYSES KEVIN E. TRENBERTH JERRY G. OLSON WILLIAM G. LARGE T (ANNUAL) 90N 60N 30N 0 30S 60S 90S- 0 30E 60E 90E 120E 150E 180 150 120N 90 6W 30W 0 CLIMATE AND GLOBAL DYNAMICS DIVISION I NATIONAL CENTER FOR ATMOSPHERIC RESEARCH BOULDER. COLORADO I Table of Contents Preface . v Acknowledgments . .. v 1. Introduction . 1 2. D ata . .. 6 3. The drag coefficient . .... 8 4. Mean annual cycle . 13 4.1 Monthly mean wind stress . .13 4.2 Monthly mean wind stress curl . 18 4.3 Sverdrup transports . 23 4.4 Results in tropics . 30 5. Comparisons with Hellerman and Rosenstein . 34 5.1 Differences in wind stress . 34 5.2 Changes in the atmospheric circulation . 47 6. Interannual variations . 55 7. Conclusions ....................... 68 References . 70 Appendix I ECMWF surface winds .... 75 Appendix II Curl of the wind stress . 81 Appendix III Stability fields . 83 iii Preface Computations of the surface wind stress over the global oceans have been made using surface winds from the European Centre for Medium Range Weather Forecasts (ECMWF) for seven years. The drag coefficient is a function of wind speed and atmospheric stability, and the density is computed for each observation. Seven year climatologies of wind stress, wind stress curl and Sverdrup transport are computed and compared with those of other studies. The interannual variability of these quantities over the seven years is presented. Results for the long term and individual monthly means are archived and available at NCAR. -
SEMESTER at SEA COURSE SYLLABUS Colorado State
SEMESTER AT SEA COURSE SYLLABUS Colorado State University, Academic Partner Voyage: Spring 2022 Discipline: Natural Resources Course Number and Title: NR 150 Oceanography Division: Lower Faculty Name: Ursula Quillmann Semester Credit Hours: 3 Prerequisites: None COURSE DESCRIPTION Studying the ocean while voyaging on the ocean is a dream-come-true. We will study in the classroom the fundamentals of the four major disciplines in oceanography, 1.) Geological Oceanography (GO), Chemical Oceanography (CO), Physical Oceanography (PO), and Biological Oceanography (BO), and how together they shape our environment and Earth’s climate. The exciting part is that we will see the interaction of these four disciplines coming to life throughout the voyage. We will spend time together on the deck, observing the ocean and hopefully seeing wildlife. We will also discuss the changing ocean environments, including ocean warming, acidification, sea level rise. We will also discuss the pressures humans exert on the marine environments, including pollution, overfishing, destroying coastal habitats. Port discovery will give us a chance to evaluate the role the ocean plays in ten countries and to compare the health of the marine environment in these countries. Before each port, we will look at the pressing coastal marine issues each country is facing, and we will allow ample time to share our experiences with one another and learn from one another. This voyage allows the unique opportunity to see the big picture on how our ocean provides essential services to us. The overarching goal of studying the ocean on our voyage is to become aware that the ocean is our lifeline. -
Ocean and Climate
Ocean currents II Wind-water interaction and drag forces Ekman transport, circular and geostrophic flow General ocean flow pattern Wind-Water surface interaction Water motion at the surface of the ocean (mixed layer) is driven by wind effects. Friction causes drag effects on the water, transferring momentum from the atmospheric winds to the ocean surface water. The drag force Wind generates vertical and horizontal motion in the water, triggering convective motion, causing turbulent mixing down to about 100m depth, which defines the isothermal mixed layer. The drag force FD on the water depends on wind velocity v: 2 FD CD Aa v CD drag coefficient dimensionless factor for wind water interaction CD 0.002, A cross sectional area depending on surface roughness, and particularly the emergence of waves! Katsushika Hokusai: The Great Wave off Kanagawa The Beaufort Scale is an empirical measure describing wind speed based on the observed sea conditions (1 knot = 0.514 m/s = 1.85 km/h)! For land and city people Bft 6 Bft 7 Bft 8 Bft 9 Bft 10 Bft 11 Bft 12 m Conversion from scale to wind velocity: v 0.836 B3/ 2 s A strong breeze of B=6 corresponds to wind speed of v=39 to 49 km/h at which long waves begin to form and white foam crests become frequent. The drag force can be calculated to: kg km m F C A v2 1200 v 45 12.5 C 0.001 D D a a m3 h s D 2 kg 2 m 2 FD 0.0011200 Am 12.5 187.5 A N or FD A 187.5 N m m3 s For a strong gale (B=12), v=35 m/s, the drag stress on the water will be: 2 kg m 2 FD / A 0.00251200 35 3675 N m m3 s kg m 1200 v 35 C 0.0025 a m3 s D Ekman transport The frictional drag force of wind with velocity v or wind stress x generating a water velocity u, is balanced by the Coriolis force, but drag decreases with depth z. -
Arxiv:1809.01376V1 [Astro-Ph.EP] 5 Sep 2018
Draft version March 9, 2021 Typeset using LATEX preprint2 style in AASTeX61 IDEALIZED WIND-DRIVEN OCEAN CIRCULATIONS ON EXOPLANETS Weiwen Ji,1 Ru Chen,2 and Jun Yang1 1Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, 100871, Beijing, China 2University of California, 92521, Los Angeles, USA ABSTRACT Motivated by the important role of the ocean in the Earth climate system, here we investigate possible scenarios of ocean circulations on exoplanets using a one-layer shallow water ocean model. Specifically, we investigate how planetary rotation rate, wind stress, fluid eddy viscosity and land structure (a closed basin vs. a reentrant channel) influence the pattern and strength of wind-driven ocean circulations. The meridional variation of the Coriolis force, arising from planetary rotation and the spheric shape of the planets, induces the western intensification of ocean circulations. Our simulations confirm that in a closed basin, changes of other factors contribute to only enhancing or weakening the ocean circulations (e.g., as wind stress decreases or fluid eddy viscosity increases, the ocean circulations weaken, and vice versa). In a reentrant channel, just as the Southern Ocean region on the Earth, the ocean pattern is characterized by zonal flows. In the quasi-linear case, the sensitivity of ocean circulations characteristics to these parameters is also interpreted using simple analytical models. This study is the preliminary step for exploring the possible ocean circulations on exoplanets, future work with multi-layer ocean models and fully coupled ocean-atmosphere models are required for studying exoplanetary climates. Keywords: astrobiology | planets and satellites: oceans | planets and satellites: terrestrial planets arXiv:1809.01376v1 [astro-ph.EP] 5 Sep 2018 Corresponding author: Jun Yang [email protected] 2 Ji, Chen and Yang 1. -
Coastal Upwelling Revisited: Ekman, Bakun, and Improved 10.1029/2018JC014187 Upwelling Indices for the U.S
Journal of Geophysical Research: Oceans RESEARCH ARTICLE Coastal Upwelling Revisited: Ekman, Bakun, and Improved 10.1029/2018JC014187 Upwelling Indices for the U.S. West Coast Key Points: Michael G. Jacox1,2 , Christopher A. Edwards3 , Elliott L. Hazen1 , and Steven J. Bograd1 • New upwelling indices are presented – for the U.S. West Coast (31 47°N) to 1NOAA Southwest Fisheries Science Center, Monterey, CA, USA, 2NOAA Earth System Research Laboratory, Boulder, CO, address shortcomings in historical 3 indices USA, University of California, Santa Cruz, CA, USA • The Coastal Upwelling Transport Index (CUTI) estimates vertical volume transport (i.e., Abstract Coastal upwelling is responsible for thriving marine ecosystems and fisheries that are upwelling/downwelling) disproportionately productive relative to their surface area, particularly in the world’s major eastern • The Biologically Effective Upwelling ’ Transport Index (BEUTI) estimates boundary upwelling systems. Along oceanic eastern boundaries, equatorward wind stress and the Earth s vertical nitrate flux rotation combine to drive a near-surface layer of water offshore, a process called Ekman transport. Similarly, positive wind stress curl drives divergence in the surface Ekman layer and consequently upwelling from Supporting Information: below, a process known as Ekman suction. In both cases, displaced water is replaced by upwelling of relatively • Supporting Information S1 nutrient-rich water from below, which stimulates the growth of microscopic phytoplankton that form the base of the marine food web. Ekman theory is foundational and underlies the calculation of upwelling indices Correspondence to: such as the “Bakun Index” that are ubiquitous in eastern boundary upwelling system studies. While generally M. G. Jacox, fi [email protected] valuable rst-order descriptions, these indices and their underlying theory provide an incomplete picture of coastal upwelling. -
Shifting Surface Currents in the Northern North Atlantic Ocean Sirpa
I, Source of Acquisition / NASA Goddard Space mght Center Shifting surface currents in the northern North Atlantic Ocean Sirpa Hakkinen (1) and Peter B. Rhines (2) (1) NASA Goddard Space Flight Center, Code 614.2, Greenbelt, RID 20771 (2) University of Washington, Seattle, PO Box 357940, WA 98195 Analysis of surface drifter tracks in the North Atlantic Ocean from the time period 1990 to 2006 provides the first evidence that the Gulf Stream waters can have direct pathways to the Nordic Seas. Prior to 2000, the drifters entering the channels leading to the Nordic Seas originated in the western and central subpolar region. Since 2001 several paths fiom the western subtropics have been present in the drifter tracks leading to the Rockall Trough through wfuch the most saline North Atlantic Waters pass to the Nordic Seas. Eddy kinetic energy fiom altimetry shows also the increased energy along the same paths as the drifters, These near surface changes have taken effect while the altimetry shows a continual weakening of the subpolar gyre. These findings highlight the changes in the vertical structure of the northern North Atlantic Ocean, its dynamics and exchanges with the higher latitudes, and show how pathways of the thermohaline circulation can open up and maintain or increase its intensity even as the basin-wide circulation spins down. Shifting surface currents in the northern North Atlantic Ocean Sirpa Hakkinen (1) and Peter B. Rhines (2) (1) NASA Goddard Space Flight Center, Code 614.2, Greenbelt, MD 20771 (2) University of Washington, Seattle, PO Box 357940, WA 98195 Inflows to the Nordic seas from the main North Atlantic pass through three routes: through the Rockall Trough to the Faroe-Shetland Channel, through the Iceland basin over the Iceland-Faroe Ridge and via the Irminger Current passing west of Iceland. -
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. -
Lecture 4: OCEANS (Outline)
LectureLecture 44 :: OCEANSOCEANS (Outline)(Outline) Basic Structures and Dynamics Ekman transport Geostrophic currents Surface Ocean Circulation Subtropicl gyre Boundary current Deep Ocean Circulation Thermohaline conveyor belt ESS200A Prof. Jin -Yi Yu BasicBasic OceanOcean StructuresStructures Warm up by sunlight! Upper Ocean (~100 m) Shallow, warm upper layer where light is abundant and where most marine life can be found. Deep Ocean Cold, dark, deep ocean where plenty supplies of nutrients and carbon exist. ESS200A No sunlight! Prof. Jin -Yi Yu BasicBasic OceanOcean CurrentCurrent SystemsSystems Upper Ocean surface circulation Deep Ocean deep ocean circulation ESS200A (from “Is The Temperature Rising?”) Prof. Jin -Yi Yu TheThe StateState ofof OceansOceans Temperature warm on the upper ocean, cold in the deeper ocean. Salinity variations determined by evaporation, precipitation, sea-ice formation and melt, and river runoff. Density small in the upper ocean, large in the deeper ocean. ESS200A Prof. Jin -Yi Yu PotentialPotential TemperatureTemperature Potential temperature is very close to temperature in the ocean. The average temperature of the world ocean is about 3.6°C. ESS200A (from Global Physical Climatology ) Prof. Jin -Yi Yu SalinitySalinity E < P Sea-ice formation and melting E > P Salinity is the mass of dissolved salts in a kilogram of seawater. Unit: ‰ (part per thousand; per mil). 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. (from Global Physical Climatology ) ESS200A Prof. Jin -Yi Yu Low density due to absorption of solar energy near the surface. DensityDensity Seawater is almost incompressible, so the density of seawater is always very close to 1000 kg/m 3. -
On the Coupling of Wind Stress and Sea Surface Temperature
15 APRIL 2006 SAMELSON ET AL. 1557 On the Coupling of Wind Stress and Sea Surface Temperature R. M. SAMELSON,E.D.SKYLLINGSTAD,D.B.CHELTON,S.K.ESBENSEN,L.W.O’NEILL, AND N. THUM College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon (Manuscript received 25 January 2005, in final form 5 August 2005) ABSTRACT A simple quasi-equilibrium analytical model is used to explore hypotheses related to observed spatial correlations between sea surface temperatures and wind stress on horizontal scales of 50–500 km. It is argued that a plausible contributor to the observed correlations is the approximate linear relationship between the surface wind stress and stress boundary layer depth under conditions in which the stress boundary layer has come into approximate equilibrium with steady free-atmospheric forcing. Warmer sea surface temperature is associated with deeper boundary layers and stronger wind stress, while colder temperature is associated with shallower boundary layers and weaker wind stress. Two interpretations of a previous hypothesis involving the downward mixing of horizontal momentum are discussed, and it is argued that neither is appropriate for the warm-to-cold transition or quasi-equilibrium conditions, while one may be appropriate for the cold-to-warm transition. Solutions of a turbulent large-eddy simulation numerical ␥ model illustrate some of the processes represented in the analytical model. A dimensionless ratio A is introduced to measure the relative influence of lateral momentum advection and local surface stress on the ␥ Ͻ boundary layer wind profile. It is argued that when A 1, and under conditions in which the thermo- dynamically induced lateral pressure gradients are small, the boundary layer depth effect will dominate lateral advection and control the surface stress. -
Evaluation of Subtropical North Atlantic Ocean Circulation in CMIP5 Models Against the Observational Array at 26.5°N and Its Changes Under Continued Warming
1DECEMBER 2018 B E A D L I N G E T A L . 9697 Evaluation of Subtropical North Atlantic Ocean Circulation in CMIP5 Models against the Observational Array at 26.5°N and Its Changes under Continued Warming R. L. BEADLING,J.L.RUSSELL,R.J.STOUFFER, AND P. J. GOODMAN Department of Geosciences, The University of Arizona, Tucson, Arizona (Manuscript received 12 December 2017, in final form 16 September 2018) ABSTRACT Observationally based metrics derived from the Rapid Climate Change (RAPID) array are used to assess the large-scale ocean circulation in the subtropical North Atlantic simulated in a suite of fully coupled climate models that contributed to phase 5 of the Coupled Model Intercomparison Project (CMIP5). The modeled circulation at 26.58N is decomposed into four components similar to those RAPID observes to estimate the Atlantic meridional overturning circulation (AMOC): the northward-flowing western boundary current (WBC), the southward transport in the upper midocean, the near-surface Ekman transport, and the south- ward deep ocean transport. The decadal-mean AMOC and the transports associated with its flow are captured well by CMIP5 models at the start of the twenty-first century. By the end of the century, under representative concentration pathway 8.5 (RCP8.5), averaged across models, the northward transport of waters in the upper 2 WBC is projected to weaken by 7.6 Sv (1 Sv [ 106 m3 s 1; 221%). This reduced northward flow is a combined result of a reduction in the subtropical gyre return flow in the upper ocean (22.9 Sv; 212%) and a weakened net southward transport in the deep ocean (24.4 Sv; 228%) corresponding to the weakened AMOC. -
Modification of the Charnock Wind Stress Formula to Include the Effects of Free Convection and Swell
3 Modification of the Charnock Wind Stress Formula to Include the Effects of Free Convection and Swell C.H. Huang U.S. Department of the Interior, Bureau of Ocean Energy Management, Regulation, and Enforcement, USA 1. Introduction The estimate of the surface fluxes of momentum, sensible heat, and water vapor over the ocean is important in numerical modeling for weather forecasting, air quality modeling, environmental impact assessment, and climate modeling, which, in particular, requires more accurate flux calculations. The accuracy of flux calculations depends on an important parameter: the surface roughness length. More than five decades ago Charnock (1955) formulated the surface roughness length over the ocean, relating the sea-surface roughness to wind stress on the basis of dimensional argument. Even now the Charnock wind stress formula is widely used. However, in the free convection limit, the horizontal mean wind speed and the wind stress approach zero, therefore the friction velocity also approaches zero; in this condition, the Charnock wind stress formula is no longer applicable and the Monin-Obukhov similarity theory (MOST) has a singularity; MOST relies on the dimensional analysis of relevant key parameters that characterize the flow behavior and the structure of turbulence in the atmospheric surface layer. Thus, in the conditions of free convection, the traditional MOST is no longer valid, because the surface roughness length also approaches zero. In numerical modeling, the surface fluxes, wind, and temperature in the surface layer are important, because they are used as lower boundary conditions. In the Charnock formulation of surface roughness, two important physical processes were not considered: one is the free convection and the other is the swell. -
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.