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# Oceanography/Barotropic Tidal Forcing

Question
Hi Randy

I appreciate if you can explain what is "Barotropic Tidal Forcing", and what is the difference between Barotropic and Baroclinic tides?

Thanks,
Kevin

Hi Kevin,

In general, the term barotropic means motion that occurs in phase over the entire water column, i.e., motion at the surface occurs at the same time as motion at depth, although not necessarily at the same amplitude (surface amplitudes are higher). Baroclinic means motions that have vertical structure and may not have any surface expression at all. Internal waves are an example of baroclinic motion.

The main component of tides is barotropic with the motions in phase with the gravitational influence of the moon and sun (the M2 tide is the largest). These components are the ones typically displayed in tide charts. The amplitudes of the motions are influenced by the ocean boundaries (coastlines and depth) and so can vary a lot from location to location. For the M2 tide, say, the bulging of the water nearest the moon, as the Earth rotates, forms in a sense a 'tidal wave' which causes water to slosh around the boundaries, giving rise to raising and lowering water levels and ebbing and flowing currents.

When the water being forced by the barotropic tide encounters undersea topography, the water is diverted vertically where it can encounter a different surrounding density. It then responds as a gravity wave, seeking to get back to its own density level. This generates a big internal wave, being forced at the tidal frequency. The particular wavelength, frequency and amplitude of the waves depend on the actual conditions. The propagating energy represents a baroclinic tide.

Here's a pretty readable article that describes internal tides

http://www.tos.org/oceanography/archive/18-4_robertson.pdf

Good luck!
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Oceanography

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#### randy patton

##### Expertise

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

##### Experience

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).

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

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

Past/Present Clients
Currently an Expert for All Experts in Advanced Math