Your IP: 38.107.179.211 United States Near: United States

Lookup IP Information

1 2 3 4 5 6 7 8 Next

Below is the list of all allocated IP address in 45.4.0.0 - 45.4.255.255 network range, sorted by latency.

Ekman Transport is the net motion of fluid as the result of a balance between Coriolis and turbulent drag forces. In the picture above, the wind blowing North creates a surface stress and a resulting Ekman spiral is found below it in the water column. Ekman transport, part of Ekman motion theory first investigated in 1902 by Vagn Walfrid Ekman (for whom it is named), is the term given for the 90 degree net transport of the surface layer (depth to which wind penetrates) due to wind forcings. This phenomenon was first noted by Fridtjof Nansen, who recorded that ice transport appeared to occur at an angle to the wind direction during his arctic expedition during the 1890s.[1] The direction of transport is dependent on the hemisphere. In the northern hemisphere this transport is at a 90 degree angle to the right of the direction of the wind, and in the southern hemisphere it occurs at a 90 degree angle to the left of the direction of the wind.[2] Contents 1 Theory 2 Mathematical derivation 3 Applications 4 Notes 5 References 6 Links 7 External Links // Theory Ekman theory explains the theoretical state of circulation if water currents were driven only by the transfer of momentum from the wind. In the physical world this is difficult to observe due to the presence of many other current driving forces (i.e. pressure and density gradients). Though the following theory technically applies to this ideal situation in which only wind drives circulation, Ekman motion describes the wind driven portion of surface circulation seen in the surface layer.[3][4] Surface currents flow at a 45 degree angle to the wind due to a balance between the Coriolis force and the drags generated by the wind and the water.[5] If the ocean is divided vertically into thin layers, the magnitude of the velocity (the speed) decreases from a maximum at the surface until it dissipates. The direction also shifts slightly across each subsequent layer (right in the northern hemisphere and left in the southern hemisphere). This is called the Ekman spiral.[6] The layer of water from the surface to the point of dissipation of this spiral is known as the Ekman layer. If all flow over the Ekman layer is integrated, the net transportation is at an angle of 90 degrees to the right (left) of the surface wind in the northern (southern) hemisphere.[2] Mathematical derivation Some assumptions of the fluid dynamics involved in the process must be made in order to simplify the process to a point where it is solvable. The assumptions made by Ekman were:[7] No boundaries Infinitely deep water Eddy viscosity, , is constant (this is now known not to be totally true) The wind forcing is steady and has been blowing for a long time Barotropic conditions with no geostrophic flow The Coriolis parameter, is kept constant The simplified equations for the Coriolis force in the x and y directions follow from these assumptions: 1) 2) where is the wind stress, is the density, is the East-West velocity, and is the north-south velocity. Integrating each equation over the entire Ekman layer 3) 4) where 5) 6) Here and represent the zonal and meridional mass transport terms with units of mass per unit time per unit length. Contrarily to common logic, north-south winds cause mass transport in the East-West direction.[8] In order to understand the vertical velocity structure of the water column, equations 1 and 2 can be rewritten in terms of the vertical eddy viscosity term. 7) 8) where is the vertical eddy viscosity coefficient This gives a set of differential equations of the form 9) 10) In order to solve this system of two differential equations, two boundary conditions can be applied: as Friction is equal to wind stress at the free surface () Things can be further simplified by considering wind blowing in the y-direction only. This means is the results will be relative to a north-south wind (although these solutions could be produced relative to wind in any other direction):[9] 11) 12) where and represent Ekman transport in the u and v direction In equation 11 the plus sign applies to the northern hemisphere and the minus sign to the southern hemisphere. is the wind stress on the sea surface is the Ekman depth (depth of Ekman layer) By solving this at z=0, the surface current is found to be (as expected) 45 degrees to the right (left) of the wind in the Northern (Southern) Hemisphere. This also gives the expected shape of the Ekman spiral, both in magnitude and direction.[9] Integrating these equations over the Ekman layer shows that the net Ekman transport term is 90 degrees to the right (left) of the wind in the Northern (Southern) Hemisphere. Applications Ekman transport is a factor in coastal upwelling regimes which provide the nutrient supply for some of the largest fishing markets on the planet.[10] Wind in these regimes blows parallel to the coast (such as along the coast of Peru, where the wind blows North). From Ekman transport, surface water has a net movement of 90 degrees to the left in such a location. Because the surface water flows away from the coast, the water must be replaced with water from below.[11] It is important to remember that in shallow coastal waters, the Ekman spiral is normally not fully formed and the wind events that cause upwelling episodes are typically rather short. This leads to many variations in the extent of upwelling, but the ideas are still generally applicable.[12] Ekman transport is also similarly at work in equatorial upwelling, where the eastward component of the trade winds causes net poleward water transport in both hemispheres[10] On smaller scales, cyclonic winds induce Ekman transport which causes net divergence and upwelling, or Ekman pumping,[10] while anti-cyclonic winds cause net convergence and downwelling, or Ekman suction[13] Ekman transport is also a factor in the circulation of the ocean gyres. Ekman transport causes water to flow toward the center of the gyre in all locations, creating a sloped sea-surface, and initiating geostrophic flow (Colling p 65). Harald Sverdrup applied Ekman transport while including pressure gradient forces to develop a theory for this (see Sverdrup balance).[13] Notes ^ Pond & Pickard, p 101 ^ a b Colling, pp 42-44 ^ Colling p 44 ^ Sverdrup p 228 ^ Mann & Lazier p 169 ^ Knauss p 124. ^ Pond & Pickard p. 106 ^ Knauss p. 123 ^ a b Pond & Pickard p.108 ^ a b c Knauss p 125 ^ Mann & Lazier p 172 ^ Colling p 43 ^ a b Pond & Pickard p 295 References Colling, A., Ocean Circulation, Open University Course Team. Second Edition. 2001. ISBN 978-0-7506-5278-0 Knauss, J.A., Introduction to Physical Oceanography, Waveland Press. Second Edition. 2005. ISBN 978-1-57766-429-1 Mann, K.H. and Lazier J.R., Dynamics of Marine Ecosystems, Blackwell Publishing. Third Edition. 2006. ISBN 978-1-405-11118-8 Pond, S. and Pickard, G. L., Introductory Dynamical Oceanography, Pergamon Press. Second edition. 1983. ISBN 978-0-080-28728-7 Sverdrup, K.A., Duxbury, A.C., Duxbury, A.B., An Introduction to The World's Oceans, McGraw-Hill. Eighth Edition. 2005. ISBN 978-0-07-294555-9 Links Ekman Layer Ekman Spiral External Links What is Ekman transport ? A figure explaining Ekman transport v • d • e Ocean currents and gyres Currents Arctic Ocean East Greenland · Norwegian Atlantic Ocean Agulhas · Angola · Antilles · Azores · Baffin Island · Benguela · Brazil · Canary · Cape Horn · Caribbean · East Greenland · East Iceland · Falkland · Florida · Guinea · Gulf Stream · Irminger · Labrador · Lomonosov · Loop · North Atlantic · North Brazil · North Equatorial · Norwegian · Portugal · Slope Jet · South Atlantic · South Equatorial · Spitsbergen · West Greenland Indian Ocean Agulhas · East Madagascar · Equatorial Counter Current · Indian Monsoon Current · Indonesian Throughflow · Leeuwin · Madagascar · Mozambique · Somali · South Australian · South Equatorial · West Australian Pacific Ocean Alaska · Aleutian · California · Cromwell · East Australia · Equatorial Counter Current · Humboldt · Indonesian Throughflow · Kamchatka · Kuroshio · Mindanao · North Equatorial · North Pacific · Oyashio · South Equatorial Southern Ocean Antarctic Circumpolar Current Gyres Major gyres Indian Ocean Gyre · North Atlantic Gyre · South Atlantic Gyre · North Pacific Gyre · South Pacific Gyre Other gyres Beaufort Gyre · Indian Monsoon Gyre · Ross Gyre · Weddell Gyre Related Atmospheric circulation · Boundary currents · Coriolis effect · Ekman transport · Great Pacific Garbage Patch · Marine debris · North Atlantic Garbage Patch · Ocean · Thermohaline circulation   Physical oceanography - Waves and Currents Waves Airy wave theory · Ballantine Scale · Boussinesq approximation · Breaking wave · Clapotis · Cnoidal wave · Cross sea · Dispersion · Infragravity waves · Edge wave · Equatorial waves · Fetch · Freak wave · Gravity wave · Internal wave · Kelvin wave · Luke's variational principle · Mild-slope equation · Radiation stress · Rogue wave · Rossby wave · Rossby-gravity waves · Sea state · Seiche · Significant wave height · Sneaker wave · Soliton · Stokes drift · Surf wave · Swells · Tsunami · Undertow · Ursell number · Wave base · Wave–current interaction · Wave height · Wave power · Wave shoaling · Wave radar · Wave turbulence · Waves and shallow water · Shallow water equations · Wind wave · Wind wave model · More... Circulation Atmospheric circulation · Baroclinity · Boundary current · Coriolis effect · Downwelling · Eddy · Ekman layer · Ekman spiral · Ekman transport · El Niño-Southern Oscillation · Geostrophic current · Gulf Stream · Halothermal circulation · Humboldt Current · Hydrothermal circulation · Global circulation model · Langmuir circulation · Longshore drift · Loop Current · Maelstrom · Ocean current · Ocean dynamics · Ocean gyre · Rip current · Thermohaline circulation · Shutdown of thermohaline circulation · Subsurface currents · Sverdrup balance · Whirlpool · Upwelling · GLODAP · MOM · WOCE · More... Tides Amphidromic point · Earth tide · Head of tide · Internal tide · Lunitidal interval · Perigean spring tide · Rule of twelfths · Slack water · Spring/neap tide · Tidal bore · Tidal force · Tidal power · Tidal race · Tidal range · Tidal resonance · Tide · Tide gauge · Tideline · More...   Physical oceanography - Other Landforms Abyssal fan · Abyssal plain · Atoll · Bathymetric chart · Cold seep · Continental margin · Continental rise · Continental shelf · Contourite · Hydrography · Guyot · Oceanic basin · Oceanic plateau · Oceanic trench · Passive margin · Seabed · Seamount · Submarine canyon · Coastal geography · More... Plate tectonics Black smoker · Convergent boundary · Divergent boundary · Fracture zone · Hydrothermal vent · Marine geology · Mid-ocean ridge · Mohorovičić discontinuity · Vine–Matthews–Morley hypothesis · Oceanic crust · Outer trench swell · Ridge-push · Seafloor spreading · Slab window · Subduction · Transform fault · Volcanic arc · More... Ocean zones Benthic · Deep ocean water · Deep sea · Littoral · Mesopelagic · Oceanic zone · Pelagic · Photic Sea level Current sea level rise · Future sea level · Sea-level curve · DART · GLOSS · NOOS · OSTM · WGS Acoustics Ocean acoustic tomography · Sofar bomb · SOFAR channel · Underwater acoustics · Hydroacoustics Other Alvin · Argo · Benthic lander · Color of water · Marginal sea · Mooring · Ocean · Ocean energy · Ocean exploration · Ocean observations · Ocean pollution · Ocean reanalysis · Ocean surface topography · Ocean thermal energy conversion · Oceanography · Pelagic sediments · Sea surface microlayer · Sea surface temperature · Seawater · Science On a Sphere · Thermocline · Underwater glider · Water column · World Ocean Atlas · NODC · More... This oceanography article is a stub. You can help Wikipedia by expanding it. v • d • e