# Tag Info

18

Theoretically, I agree that there should be one instable equilibrium point between the two stable equilibrium points when we have a 2D current field. However, there are some additional components of the problem: Ocean currents are not 2D but 3D currents. Considering only the sea surface might lets field lines disappear. The wind has an additional forcing. ...

18

Yes, you're right, there should be (at least one) saddle point in the middle of the loop. And indeed, if you search for illustrations of Pacific ocean circulation, you can see the saddle point in some of them, like this one: Source: Introduction to Tropical Meteorology, 2nd ed., chapter 3.3.1, fig. 3.20. Now, in a lot of other maps, the saddle region is ...

17

The cause for this phenomenon is sand and silt moving down an underwater cliff as you guessed. The geography that makes this possible is as follows. The island of Mauritius is located on a giant plateau that was created by seafloor spreading a few million years ago. Most of which is under 8-150 meters of water. Where the waterfall effect occurs there is ...

13

You are looking for the drag force imposed by the fluid flow on an object: $$F = \dfrac{1}{2} \rho v^{2} C_D A$$ where $\rho$ is the density of the fluid, $v$ is the speed of the flow, $C_D$ is the drag coefficient depending on the shape of the object, and $A$ is the surface area normal to the fluid flow. Let's plug in some characteristic numbers for ...

13

I'm not familiar with land-based methods, but for global measurements, one method is to use satellite altimetry (I'm more familiar with the geodesy side, but many of the same satellites are used). I think many of the current methods interpolate global or regional currents from a sparse network of buoys. As more radar satellites are launched, however, ...

12

As SimonW points out strong tidal currents will modify the wave shape and significant height. The Wolf & Prandle (1999) study provides a neat summary description of the effects of currents (of any kind) on waves: (i) Wave generation by wind—the effective wind is that relative to the surface current, and the wave age (cp/U*) and effective surface ...

12

Your best bet without modern tools would be a sextant and the proper maps for celestial navigation. This is a time-tested and old method of navigation no longer in regular use, but it probably doesn't meet your "no over-technical methods" criterion as it requires a tool, maps and knowledge of its use. If you only had knowledge of the constellations and a ...

12

There are few known mechanisms that lead to the generation of Rogue waves, such as the ones you mentioned, but essentially all Rogue waves are the due to the nonlinear wave dispersion characteristics of large groups of waves. I can imagine one approach to predicting the emergence of such waves is to simulate the evolution of initial wave states with Navier-...

10

A very good analysis looking at the 3% relationship is an article by Weber (1983). His main result is that: We assume a fully developed sea, and take the eddy viscosity to be proportional to the friction velocity times a characteristic depth. Hence the total current (Ekman current plus wave-induced current) can be expressed as functions of the wind speed....

10

Great question. These features are mesoscale Eddies and they are akin to hurricanes in the atmosphere. They are the ocean’s high or low pressure systems and are the result of instabilities. The cyclonic eddy (counterclockwise direction in the northern hemisphere) is called a cold-core eddy and the anti-cyclonic eddy is called a warm-core eddy. Unlike ...

8

Oceanic topography of the sea surface $\zeta$ can be defined as the height of the sea surface relative to a particular level surface, the geoid. The geoid to be the level surface that coincided with the surface of the ocean at rest (a list of geoids with application to oceanography can be found in Talone et al., 2014). Variations in sea surface height (...

8

Warm water does hold more salt - at saturation, but seawater isn't even close to saturation. Surface sea water gets warm, starts to evaporate (hence clouds) and therefore gets denser. So it sinks to the ocean floor, where it cools down to about 4 deg Celsius, and gets denser still. But it still is a very long way from being saturated with salt, so 'how much ...

8

Remember that 360° == 0°. They're the same line of longitude. So the gap between 359° and 0° is no more than the gap between 1° and 2°, and should be handled the same way.

7

Direct measurements of three-dimensional ocean currents are carried out with acoustic Doppler current profilers (ADCPs). The ADCPs are usually moored and bottom mounted instead of being ship-based or attached to a floating mooring to minimize the vertical displacement associated with the vertical motions of the ocean surface caused by waves. The ADCP does ...

7

In some capacity, differential heating is responsible for convective motion of the ocean due to buoyant forces. However, it is possible to show that the net (vertically integrated) horizontal transport in most of the ocean is solely due to the action of the wind stress on the water surface (Sverdrup, 1947). In other words, the pattern of major ocean currents ...

7

There's a pretty good rundown of this issue over at RealClimate, and a wikipedia article dedicated to the topic. A summary of the main points from there: The Gulf Stream is part of the Meridional Overturning Current (global ocean conveyor), which is primarily wind-driven, and secondarily thermohaline-driven. The Gulf Stream itself is also primarily wind-...

7

I think, there are two factors which prevent the forming of clusters of floats: The floats' lifespan. Batteries supposedly last for four years, then the floats become debris which sink to the bottom of the ocean (yeah, not that great from an environmentalist point of view). So the lifespan of the battery prevents the floats from clustering. The introdcution ...

7

Tide prediction at some locale is more of an empirical art rather than an analytic science. It essentially is a reduction of decades or centuries of historical tide levels at the locale to Fourier-like coefficients. Tides at a locale are modeled as a sum of various frequency components, each with a magnitude and a phase offset from some reference. The ...

6

It looks like a Gibbs oscillation, a basic feature of spectral analysis. In a spectral atmospheric model this means that near high orography artificial surface waves exist which may reflect in different variables. They are usually not considered to affect meteorology, however. onlinelibrary.wiley.com/doi/10.1029/2010JC006927/full http://journals.ametsoc.org/...

6

Joe Kington has provided an excellent answer re sensing from space. Torbjørn T. pointed out in a comment that the site that I linked for context actually has a good explanation... so after blushing slightly, I shall summarise it here. People with more specialist knowledge are, of course, welcome to elaborate or correct any misunderstanding. Incidentally, it ...

6

Ocean currents can be described as flow oscillations that are forced at different frequencies. In the absence of any external forces (wind, friction), the resulting flow is the inertial motion, which is the response to the balance between Coriolis and inertia. The Coriolis parameter, $f$, can be described as a frequency: the effective planetary rotation ...

6

The survivors would probably end up in Jutland or Norway, maybe Sweden due to the currents. CC BY-SA 3.0 The main wind pattern is also western, but with prevailing eastern winds, they might end up in Scotland, depending on the vessel. The Jutlandic coast has experienced a large number of shipwrecks in the past. DMI Even if a boat gets out on the open ...

5

I think the simplest answer is through water mass formation, the resulting thermohaline circulation, mixing caused by wind predominantly in shallow regions, and through downwelling processes. The heat exchanged with the atmosphere in the surface layers determine the temperature of the near-surface water. From there, mixing (caused by wind, for instance) will ...

5

The diagram presented in the question is a very simplified version of the meridional overturning circulation. It is overly simplistic and generally creates very large misunderstandings. A good reference to the evolution of the Meridional Overturning Circulation diagrams is the work by Richardson (2008). Just in case you don't have access to Progress in ...

5

Areas associated with velocity shear at a stratified interface are notably strong in the region of the Equatorial Undercurrent, straits (ex: strait of Gibraltar, the Bosphorus) and regions of the thermocline where internal waves are strong (South China Sea). These areas are typically associated with strong turbulence as a direct result of the strong velocity ...

5

Lyle et al. (2007), prior to the paper you mention, also came up with this idea that the ACC initiated with its modern setting (i. e. with strong currents and mixing throughout the water column) during the Late Oligocene (ca. 25 Ma), so roughly 10 Myr after the Eocene-Oligocene when the antarctic glaciation is thought to have occurred. Their evidence is ...

5

As you have noted, this technology is new, and so far only small numbers of experimental tidal energy converters (TECs) have been deployed. For this reason, little has been possible in the way of measurement, and so as you note, all estimates are based on models or other means of prediction. To answer the second question first - how much the currents are ...

5

The link is the conservation of mass equation: $$\frac{\partial u}{\partial x} + \frac{\partial v}{\partial y} + \frac{\partial w}{\partial z} = 0.$$ Briefly, Ekman pumping is the horizontal divergence of the Ekman transport. If we integrate this expression over the Ekman layer,  \int_{-D}^0 \frac{\partial u}{\partial x} dz + \int_{-D}^0 \frac{\partial ...

5

The main reason is that the Gulf Stream transports warm surface water from the tropics, driven by the thermohaline circulation. The tropical trade winds push surface water towards Western Atlantic and build up stress. Further north the dominant wind direction is towards the east. The Coriolois force also helps to move the warm water masses towards the east. ...

5

A few thoughts - assuming like you say that the aqua-planet is the same size as earth, and all else being equal, it's best to consider the two major classes of waves: Nondispersive wind generated waves: Here the maximum wave height is a function of wind speed (fetch). However, wind speed in general is not a function of wave height (unless you invoke ...

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