Oceanography/Tide size


I require understanding as given the result of the tidal difference so drastic, comparing two coasts, the Atlantic coast of Colombia of about 20 cm and the Colombian Pacific coast about 430 cm. something similar happens on both coasts of Panama

ANSWER: Variations in tidal amplitude at the coast represent a very complex process. This complexity arises from the fact that the ocean, in particular near the coast, is not in equilibrium under the influence of the diurnal (~24 hour), semi-diurnal (~12 hour ) and longer period forcings. The ocean responds to these periodic forcings, related to the time varying gravitational forces of the moon and sun, in the form of waves which propagate into adjacent regions at various speeds depending on the frequency, depth and local boundaries (coastlines).  If the forcing time scale were very long, in the sense of being much longer than the natural frequency of the excited waves, then the ocean would be expected to reach a steady state with the tidal amplitude being the same over very large regions defined by nearly spatially constant gravitational forces (the gravitational force varies with latitude). This is like pouring water in a container that has varying depth; the water will come to the same height regardless of the depth.

Thus, the amplitude of the tide at a particular location is the superposition of very long (100s of kilometers) waves. Depending on the coastline and bathymetry, the forcing of water movement may set up resonant waves that can interact with the forced oscillations and increase tidal ampitudes. The well known extreme tides of the Bay of Fundy are thought to be caused by this mechanism. The multiple forcing frequencies, varying coastlines and non-equilibrium of the ocean response all contribute to the dramatic differences in tides between various locations.

Tidal responses for an area are almost impossible to solve for based on first principles (positions of moon and sun, shape of costline, bathymetry, not to mention meteorlogical and viscous effects), but have to be fit to data in order to perform predictions.

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QUESTION: Best regards
Thank you for your prompt response and this explanation is understandable, particularly want to look at the explanations that a biologist mention about the little sea change that occurs in the Colombian Atlantic coast and he said tha is due to the location of Cuba and the Antilles. It really does not seem logical because if we compare to the Bering Sea islands has a lot more belt next to the belt of islands in the Antilles and there is no the phenomenon of water retention that attribute little tidal change.

Global M2 tide
Global M2 tide  
The short answer is that Cuba and the Antilles are not mainly responsible for the low tides in the Caribbean Sea and Columbian coast. The low tidal amplitudes in these regions are simply due to their proximity to a node of zero amplitude (an amphidrome) located near the Leeward Islands.

As we know, tidal variations ("tidal waves") are due to the complex response of the oceans to periodic, repeatable gravitational forces with periods on the order of 12 to 24 hours. Including the Coriolus force (which varies with latitude) as well as the ocean basin shape and depths gives a map of the phase (time of day) and amplitude of this response. The solution for the M2 tide (strongest) for the global oceans is shown in the attached image. This "solution" is the result of both physics-based modeling as well as fitting tidal frequency components to data (tide data).

The sizes of the Caribbean and Gulf of Mexico basins are not big enough to support a resonant mode for the diurnal (daily) and semi-diurnal (twice daily) tides, and so no enhancement occurs. So you are stuck with small tides. The existence of the islands may weaken the already small tides, but the effect is not the dominant cause of low amlitudes.


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randy patton


Physical oceanography, surface and internal wave characteristics, ocean currents, fluid mechanics, geophysical fluid dynamics, ocean optics, coastal dynamics, modeling and simulation, data analysis, El Nino and related large scale dynamics Not an expert in marine biology (some in bioluminescence) or chemical oceanography


26 years as professional scientist for research company working mostly on Navy and other government contracts. Projects included modeling, simulations and data analysis related to Non-acoustic Anti-submarine Warfare (NAASW). Other projects included remote sensing of ocean features, statistical analysis of ship tracks, ocean optics instrumentation development, synthetic aperture radar (SAR) and sonar (SAS).

Journal of Physical Oceanography, 1984, "A Numerical Model for Low-Frequency Equatorial Dynamics" (with M. Cane)

MS Physical Oceanography, MIT, 1981 BS Applied Math, UC Berkeley, 1976

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