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Topic: Ekman spiral


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In the News (Fri 19 Jul 19)

  
  Chapter09Part1
Ekman assumed that a homogenous water column was set in motion by wind blowing across its surface and, because of the CE, the top-most layer motion was 45 degrees to the right of the surface wind direction.
To visualize this Ekman spiral, I want you to imagine a spiral staircase down which you are attempting to flee from danger in a nightmare.
If this float were put into the ocean in an active wind field (of sufficient strength and duration to produce the Ekman spiral) it would act as an integrating (averaging) tool that would move in the direction of the net movement of all the water mass between the surface and the depth of frictional influence.
www4.ncsu.edu /~ceknowle/chapter09/part1.html   (1195 words)

  
 Boundary layers, Prandtl's and others - Physics Today October 2006
Ekman was the first to develop the concept of 3D boundary layers, those in which rotation (or curved flow) in a viscous fluid causes a boundary layer with a well-defined depth.
Ekman was inspired by reports that icebergs in the Northern Hemisphere generally drifted at an angle to the right of the wind direction, and he sought an explanation in the effect of Earth's rotation.
In the geophysical sciences, the wind-driven Ekman transport in the surface Ekman layer is fundamental to all theories of ocean circulation, and in the atmosphere the Ekman spiral and transport toward low pressure are fundamental to theories of hurricanes and all atmospheric vortices.
www.physicstoday.org /vol-59/iss-10/p10.html   (1160 words)

  
 AMS Glossary
The Ekman spiral is an equiangular spiral having the geostrophic wind as its limit point.
The theory of this spiral was developed by Ekman in 1902 for motion in the upper layers of the ocean under the influence of a steady wind.
As originally applied by Ekman to ocean currents, a graphic representation of the way in which the theoretical wind-driven currents in the surface layers of the sea vary with depth.
amsglossary.allenpress.com /glossary/search?id=ekman-spiral1   (411 words)

  
 Oceanography Dictionary
Spiral : The EKMAN SPIRAL is a result of the corolis force.
As wind blows across the ocean, surface waters move to the right of the wind and drag layers of water immediately beneath them in the northern hemisphere (waters move to the left of the wind in the southern hemisphere.
The net effect of the Ekman spiral is the movement of ocean waters at a 90 degree angle to the right of the direction of the wind along the ocean's surface in the Northern hemisphere (the ekman spiral moves in 90 degree angles to the left of the wind in the Southern hemisphere).
amthomas.myweb.uga.edu /edit6190/project/dictionary.htm   (544 words)

  
 Homework 4    20 ...
The Ekman spiral is the 3-D pattern of wind-driven currents decreasing in speed and drifting progressively to the right with depth (to the left in the Southern Hemisphere).
The Ekman transport is a result of the Ekman spiral that is formed by a combination of friction in the water and Coriolis force.
Ekman transport is the net movement of the water which is at a right angle to the direction of the wind in the Northern Hemisphere.
karws.gso.uri.edu /OCG123/Spring_2002/Lab_materials/HW4ans/HW4ans.html   (845 words)

  
 Chapter 1 Section 4   (Site not responding. Last check: 2007-10-20)
Ekman’s theory considers the steady state balance of friction and the Coriolis acceleration caused by Earth’s rotation.
The integrated net transport of the wind driven layer (the Ekman Spiral) is 90° to the right of the wind in the Northern Hemisphere (to the left in the Southern Hemisphere).
The net movement of water in the wind-driven layer as a result of the Ekman Transport will be away from the equator both north (90° to the right of the winds) and south (90° to the left of the winds) of the equator (gray arrows).
www.ccpo.odu.edu /~lizsmith/SEES/ocean/ocean_lectures/sst_lecture/Part_1/1_4.htm   (532 words)

  
 Ekman transport what is it?
In order to understand the term Ekman transport it is necessary to have a clear understanding of the concept known as Ekman spiral.
The Ekman spiral is a theoretical model of the effect on water of wind blowing over the ocean.
In the Ekman layer caused by winds blowing across the sea's surface, if the viscosity coefficient is not dependent on depth, the current on the sea's surface will point 45 degrees to the right of the wind's direction (in the Northern hemisphere).
www.schonwalder.org /The/Ekman.htm   (421 words)

  
 currents.html
The base of the spiral is the thermocline/pycnocline, where the density of water increases and becomes more massive, and harder to move.
Having said that the Ekman transport is at an angle of 90° to the driving wind, it is important to bear in mind that the Coriolis deflection is strongest at the poles and zero at the equator.
Due to Ekman transport, the surface layer moves at 90° to the RIGHT in the Northern Hemisphere, shown by the thick green arrows.
www.geo.umn.edu /courses/1006/Fall01_night/currents.html   (2615 words)

  
 Vagn Walfrid Ekman Summary
Ekman was a member of a consortium of Scandinavian scientists who transformed the study of oceanography and meteorology at the turn of the twentieth century.
Ekman's father, Fredrik Laurentz Ekman, was an oceanographer, but Vagn Ekman's greatest influence came from Vilhelm Bjerknes, whose work in hydrodynamics and atmospheric movements inspired Ekman to ponder similar movements in the circulation of the oceans.
Ekman held various positions as a laboratory assistant at the International Oceanographic Laboratory in Oslo, Norway, and as lecturer and professor at the University of Lund.
www.bookrags.com /Vagn_Walfrid_Ekman   (530 words)

  
 Wind-Driven Circulation and the Ekman Balance
One of the technological breakthroughs in direct confirmation of the Ekman balance was the ADCP: the shipboard ADCP in providing basin-integrals of Ekman transport and the moored ADCP in providing highly resolved profiles of current in the rugged surface regime.
The Ekman transport calculation that Dean Roemmich and I made from our transect at 11°N in the Atlantic Ocean was the first quantitative estimate of basin-integrated Ekman transport based on measured velocities in the upper ocean (Chereskin and Roemmich, 1991).
The Ekman temperature flux is sensitive to assumptions about the depth of penetration of the wind-driven flow, and therefore the Ekman depth as well as the Ekman transport are important issues for the meridional overturning circulation of the Indian Ocean.
www-ccs.ucsd.edu /~teri/ekman/ekman.htm   (891 words)

  
 Lani Aina Kai - OCN 201 Currents
The Ekman spiral is a mathematical model used to explain how the wind can blow in one direction, yet the water, on average, flows perpendicular to the wind direction.
At the base of the Ekman spiral, water is just barely moving in the opposite direction of the wind.
Ekman transport - the average direction of transport from the Ekman spiral.
www.laniainakai.com /ocean/files/ocean_notes/ocean_currents.html   (653 words)

  
 V. Walfrid Ekman - Facts, Information, and Encyclopedia Reference article
Born in Stockholm to Fredrik Laurentz Ekman, himself an oceanographer, he became committed to oceanography while studying physics at the University of Uppsala and, in particular, on hearing Vilhelm Bjerknes lecture on fluid dynamics.
Bjerknes invited Ekman, still a student, to investigate the problem and, in 1902, Ekman published his theory of the Ekman spiral which explains the phenomenon in terms of the balance between frictional effects in the ocean and the fictitious forces arising from planetary rotation.
On completing his doctorate in Uppsala in 1902, Ekman joined the International Laboratory for Oceanographic Research, Oslo where he worked for seven years, not only extending his theoretical work but also developing experimental techniques and instruments such as the Ekman current meter and Ekman water bottle.
www.startsurfing.com /encyclopedia/v/_/V._Walfrid_Ekman_e0b6.html   (245 words)

  
 Ekman layer dynamics
The total transport in the Ekman layer is the combined effect of water movement in the Ekman layer, ie the integral from the surface to the depth d
This explains why in the deep ocean the Ekman layer transport is directed at right angle to the wind direction: The transport contributions in the direction of the wind found in the upper Ekman layer are cancelled by the contributions in opposite directions found in the lower Ekman layer.
Since the surface Ekman layer is a result of wind action it is reasonable to assume that the turbulence elements responsible for the transfer of momentum are mainly the wind waves.
www.es.flinders.edu.au /~mattom/ShelfCoast/notes/chapter03.html   (2998 words)

  
 Oct 25: Ekman Transport
The details of the Ekman spiral velocity profile as a function of depth are more of theoretical interest that practical importance.
Ekman dynamics is a very practical way to estimate the oceanic response to winds on time scales of a few days.
However, Ekman transports have a far more significant impact on the entire upper ocean circulation (over much greater depths than the Ekman layer) through a rather subtle interaction with the oceanic pressure field.
marine.rutgers.edu /dmcs/ms451/2004/Notes/Wilkin20041025.htm   (511 words)

  
 Ekman Spiral 2
Nansen came to the conclusion that the tendency to drift to the right was the result of the earth's rotation.
Ekman was the first to prove this mathematically.
The velocity changes with depth in a spiral pattern, so this velocity profile is called an Ekman Spiral.
www.atmos.washington.edu /gfd_exp/exp_e/doc/ek/guide02.htm   (111 words)

  
 ESCI 485 – Air/sea Interaction
Ekman pumping results in a secondary circulation superimposed on the gyre, with convergence and downward motion in the middle of the gyre, and divergence deeper in the gyre.
Ekman transport may be important in the response of the ocean to individual storms.
Ekman transport is therefore directed off-shore, and pulls surface water away from the coast.
www.atmos.millersville.edu /~adecaria/ESCI485/esci485_lesson05_ocean_mixed_layer.html   (1702 words)

  
 Wind-Driven Circulation and the Ekman Balance
One of the technological breakthroughs in direct confirmation of the Ekman balance was the ADCP: the shipboard ADCP in providing basin-integrals of Ekman transport and the moored ADCP in providing highly resolved profiles of current in the rugged surface regime.
The Ekman transport calculation that Dean Roemmich and I made from our transect at 11°N in the Atlantic Ocean was the first quantitative estimate of basin-integrated Ekman transport based on measured velocities in the upper ocean (Chereskin and Roemmich, 1991).
The Ekman temperature flux is sensitive to assumptions about the depth of penetration of the wind-driven flow, and therefore the Ekman depth as well as the Ekman transport are important issues for the meridional overturning circulation of the Indian Ocean.
tryfan.ucsd.edu /ekman/ekman.htm   (891 words)

  
 CORIE - Modeling Benchmarks Ekman Motion
Away from the equator, a steady wind blowing over an ocean leads to ocean velocities that are not parallel to the direction of the wind.
The speed of the current is at the surface approximately 1-3% of the wind magnitude (depending on latitude and vertical eddy viscosity), and decreases exponentially with depth.
The theoretical Ekman spiral and the Ekman spiral computed at the center of the grid were compared, and can be accessed on a case-by-case basis through the table below.
www.ccalmr.ogi.edu /CORIE/modeling/elcirc/bench/ekman_bench/1.html   (450 words)

  
 SIO 210: Introduction to Physical Oceanography
Hence the red arrows are the ageostrophic component of the velocity, and correspond to the Ekman response at 15 m.
Sverdrup transport is equatorward in subtropical regions of Ekman pumping and poleward in subpolar regions of Ekman suction.
The Ekman pumping is a very small and the changes induced in the angular momentum (vorticity) are very weak.
www-pord.ucsd.edu /~ltalley/sio210/Wind_forcing   (3174 words)

  
 Geol 117 Lect 24
Ekman further showed that the net transport of water from the surface to 150 m is at 90 deg.
First of all, because Ekman transport is at right angles to the direction of prevailing wind, it actually forces water to flow into the center of a gyre, creating a "hill" of water.
When gravity and Ekman transport balance one another, there is a steady-state flow of currents parallel to the elevation contours of the hill.
ijolite.geology.uiuc.edu /02Fallclass/geo117/lectures/Lect24.html   (914 words)

  
 SIO 210: Introduction to Physical Oceanography
This direction of the "Ekman transport" is independent of the exact details of the spiral, hence exact details of the vertical eddy viscosity.
The Ekman transport components in the x and y directions (east and north) are proportional to the wind stress tau
This Ekman effect has been demonstrated by Ralph and Niiler (1999) using surface drifter data from the the Pacific (drogues at 15 m).
www-pord.ucsd.edu /~ltalley/sio210/dynamics_ekman/index.html   (549 words)

  
 Oct 18: Ekman currents
The solution is a spiraling velocity pattern that decays with depth.
From the equation for the idealized Ekman spiral solution, we see that velocity pattern depends on the details of the eddy viscosity profile.
Ekman number o(1) implies the direct influence of the winds is limited to a relatively shallow depth in the ocean
marine.rutgers.edu /dmcs/ms451/2004/Notes/Wilkin20041018.htm   (614 words)

  
 4.2 Ekman Forcing   (Site not responding. Last check: 2007-10-20)
It is assumed that the principal means for conveying wind stress to the ocean's uppermost layer is in an Ekman layer of ten's to a hundred meters thickness in which the stress is balanced by the Coriolis force.
The principal justification for the theory has been that the ocean's general circulation beneath the Ekman layer is in the proper sense as to be driven by convergent or divergent Ekman transports.
[1987] demonstrated the spiral Ekman layer structure in the subtropical North Atlantic; verification required adjusting the averaging directions daily to follow the wind.
www.agu.org /revgeophys/talley01/node6.html   (385 words)

  
 CORIE - Modeling Benchmarks
The surface current flows at 45° to the right (left) of the wind direction in the northern (southern) hemisphere, and the deviation increases over depth in a spiral pattern known as the Ekman spiral.
At the Ekman depth or depth of frictional influence of the wind, D
The Ekman transport represents the total volume of water transported at right angles to the wind direction per unit time.
www.ccalmr.ogi.edu /CORIE/modeling/elcirc/bench/ekman_bench/2.html   (368 words)

  
 Aug 30-Sep 03 VU Math Events
The boundary layer in the theory of rotating fluids, known as the Ekman layer, is between a uniform geostrophic flow and a solid boundary at which the no slip condition applies.
close to the boundary, is that the flow vector behaves as a growing spiral, the Ekman spiral, converging to the geostrophic flow while increasing the distance to the boundary.
Since the Ekman spiral solution depends on the normal component only, we have to deal with spaces of initial data nondecreasing at infinity.
www.math.vanderbilt.edu /~calendar/archive/2004/08_30.html   (530 words)

  
 P10.3 Numerical simulation of the neutral boundary layer: a comparison of enstrophy conserving with momentum conserving ...   (Site not responding. Last check: 2007-10-20)
This may in part be due to the strong emphasis that has been placed upon the subgrid scale diffusion schemes that are typically used to complement the dynamics schemes and in effect compensate for many of their flaws, in addition to acting as a physical representation of subgrid scale turbulence.
The classic Ekman solution occurs in a completely neutral atmosphere, involves a balance between simple local down-gradient subgrid scale transport, pressure gradient force, and Coriolis effect, and results in a spiral on a hodograph.
The 3-D LES of an Ekman boundary layer explicitly resolves eddies which may be responsible for nonlocal transport and thus may not necessarily result in a solution matching the classic Ekman spiral.
ams.confex.com /ams/AugAspen/techprogram/paper_14930.htm   (577 words)

  
 Chapter8   (Site not responding. Last check: 2007-10-20)
The spiral extends to a depth of approximately 100 to 150 m (330-500 ft), where the much-reduced current will be moving exactly opposite to the surface.
Over the depth of the spiral, the average flow of all the water set in motion by the wind, or the net flow (Ekman transport), moves 90° to the right or left of the surface wind, depending on the hemisphere in which the motion takes place (fig.
According to the net transport of the Ekman spiral, wind-driven water is directed toward the center of a large oceanic current gyre.
www.saddleback.cc.ca.us /faculty/jvalencic/ocean/textbook/chap8/chap8.html   (8185 words)

  
 GYRES AND EDDIES - Currents - Students - Ocean World
Ekman currents always carry water to the right of the wind in the northern hemisphere as seen in the figure.
The Ekman currents push warm water to the center of the ocean.
The mounds and depressions in the sea caused by Ekman currents, which are caused by the wind, set it.
www-ocean.tamu.edu /education/oceanworld-old/students/currents/currents4.htm   (487 words)

  
 ATMOSPHERIC TIDES   (Site not responding. Last check: 2007-10-20)
The depth of the Ekman layer is taken to be that point at which the spiral has made one complete rotation (or the e-folding scale of the decay).
The fact that the vertically-integrated mass transport in the Ekman layer is directed at 90° to the right of the surface wind is important in the distribution of ocean surface temperature.
The resultant Ekman transport is to the west, away from the coast.
www.atmos.millersville.edu /~adecaria/ESCI344/esci344_lesson06_tropical_oceans.html   (1095 words)

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