Phenomenon of long-lived ocean eddies explained

(ORDO NEWS) — Scientists from the Department of Oceanography of the Naval Postgraduate School (NPS) have explained the phenomenon of ocean circulation, which can exist from months to several years.

According to the results of a study published in the journal Geophysical Research Letters, the time of existence of stable eddies is influenced by the topography of the bottom.

Previously, physicists assumed that oceanic eddies or rings with a diameter of several tens or hundreds of kilometers should dissipate within a few weeks due to baroclinic instability – the instability of the currents of a stratified rotating liquid medium with a vertical shear of speed. However, observations show that some cycles are able to survive for ten years.

The researchers showed that the old models did not take into account the roughness of the bottom, that is, the presence of seamounts, ridges and valleys.

They used numerical simulations with a flat bottom and a bottom with realistic topography and showed that eddies over uneven surfaces persist much longer than their identical counterparts over a flat seabed.

The new model is called the “sandpaper effect”, which, by analogy with a grinding surface with abrasive particles applied to it, “smooths out” currents near the ocean floor, increasing the stability and durability of gyres on the surface.

At the same time, there is a critical height of the bottom roughness, which allows the surface rings to remain stable and retain their structure for many years.

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