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Unpredictability of Internal M2 : Volume 4, Issue 2 (20/03/2007)

By Van Haren, H.

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Book Id: WPLBN0004020995
Format Type: PDF Article :
File Size: Pages 21
Reproduction Date: 2015

Title: Unpredictability of Internal M2 : Volume 4, Issue 2 (20/03/2007)  
Author: Van Haren, H.
Volume: Vol. 4, Issue 2
Language: English
Subject: Science, Ocean, Science
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Publication Date:
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications


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Haren, H. V. (2007). Unpredictability of Internal M2 : Volume 4, Issue 2 (20/03/2007). Retrieved from

Description: Netherlands Institute for Sea Research (NIOZ), P.O. Box 59, 1790 AB Den Burg, The Netherlands. Current observations from a shelf sea, continental slopes and the abyssal North-East Atlantic Ocean are all dominated by the semidiurnal lunar (M2) tide. It is shown that motions at M2 vary at usually large barotropic and coherent baroclinic scales, >50 km horizontally and >0.5 H vertically. H represents the waterdepth. Such M2-scales are observed even close to topography, the potential source of baroclinic, internal tidal waves. In contrast, incoherent small-scale, ~10 km horizontally and ~0.1 H vertically, baroclinic motions are dominated around f, the local inertial frequency, and/or near 2Ω≈S2, the semidiurnal solar tidal frequency. Ω represents the Earth's rotational vector. This confirms earlier suggestions that small-scale baroclinic M2-motions generally do not exist in the ocean in any predictable manner, except in beams very near (<10 km horizontally) to their source. As a result, M2-motions are not directly important for generating shear and internal wave induced mixing in the ocean. Indirectly however, they may contribute to ocean mixing if transfer to small-scale motions at f and/or S2 can be proven. Also far from topography, small-scale motions are found at either or both of the latter frequencies. Different suggestions for the scales at these particular frequencies are discussed, ranging from the variability of background density gradients and associated divergence and focusing of internal wave rays to the removal of the internal tidal energy by non-linear interactions. It is noted that near f and S2 the short-wave inertio-gravity wave bounds are found in the limit of very weak stratification, which are often observed in small-scale near-homogeneous layers.

Unpredictability of internal M2

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