Polygon-70: Data Interpretation in the Light of New Concepts about Internal Waves
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gon-70: Data Interpretation in the Light of New Concepts about Internal Waves E. G. Morozov* Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia *e-mail: [email protected] Received January 22, 2020; revised March 11, 2020; accepted April 1, 2020
Abstract—We analyze our concepts about ocean dynamics and, in particular, internal waves. Our concepts have changed over the 50 years after the Polygon-70 experiment. We now understand that mesoscale eddies exist in the ocean and currents in these eddies frequently exceed the mean currents. We understand that internal tides are generated due to the interaction of tidal currents with uneven bottom topography and spread as perturbations of velocity along characteristic surfaces. The waves fill the entire ocean but are not confined to the fluctuations of the density pycnocline. An interpretation of the data on internal waves published in the 1970s has been revised in the light of our new concepts and knowledge. Keywords: Polygon-70, internal waves, characteristic equation, bottom topography, generation of internal tides DOI: 10.1134/S0001433820040076
1. INTRODUCTION: GOALS OF THE POLYGON-70 EXPERIMENT From February to October 1970, the Academy of Sciences of the Soviet Union conducted the unique Polygon-70 oceanographic hydrophysical experiment. The 50th anniversary of this scientific deed, which was a very important landmark in the history of oceanography, takes place in 2020. It was formally indicated in the plans of this experiment that it is aimed at investigating the problems of spatiotemporal variations in the oceanographic fields, the thermohaline structure of waters, and the interaction between the ocean and the atmosphere. At that time, the main result of the experiment has not been seen beyond the general words of the plan: the discovery of the synoptic (mesoscale) eddies of the open ocean and also the fact that fluctuations of the velocity fields over these scales may exceed the mean currents several times, and that synoptic eddies of the open ocean are a manifestation of Rossby waves [1]. These ideas were only in the minds of those scientists who planned Polygon-70. Six vessels from different institutes participated in the expedition, including the Dmitry Mendeleev, Akademik Kurchatov, and Andrey Vilkitsky. Measurements of currents were carried out on 17 moorings using the BPV-2 current meters, while the temperature measurements were performed using photo-thermographs. The moorings were changed approximately every 22–25 days, because the wires did not withstand long operation. A square with a size of 120 × 120 nautical miles in the center of the northeast Atlantic was selected as the study site in a deep basin called either the Cabo Verde Basin or the Gambia Abyssal Plane.
The geographical location of the study site and the hydrophysical conditions should have satisfied the conditions of the mean state of the ocean. It was thought that the bottom topography in the selected region would be relatively flat. Initially, the center of the stud
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