On Nonlinear Dynamics of Meddies

The lenses of the Mediterranean water (LMW), also known as Meddies, well distinguishable in the Atlantic Ocean water. The field observations devoted to study Meddies are presented in numerous publications and provide information on their origination, distribution, spatial scales and temporal dynamic activities. The salt-fingers and double-diffusion at the Meddies top and bottom borders may be considered as only mechanisms causing the Meddies disappearance as the thermal — saline mesoscale anomalies in the surrounding Atlantic Ocean waters. Taking into account the Medies’ realistic scales it is shown that in temporal scales of about and less than a year the Meddies water mass may be considered as invariable. Then the Meddies conservation mass is valid in such temporal scales.
The Meddies (LMW) temporal variability analysis is carried out using the theoretical approach of intrusive lens in stratified fluid extended taking into account the Coriolis force. The Meddies (LMW) are considered with the center of gravity sitting at the level of equal density. The temporal variability occurs due to the resulting effect of the set of forces: the surplus pressure originated due to the density difference between the water inside the LMW and the ambient density field; the forces originated due to both the lens’ rotation (centrifugal) and the Earth rotation (Coriolis); the forces caused by the internal wave radiation and the viscosity action. The temporal variability of LMW constitutes of two principal stages:
1) the initial, inviscid stage (“young lens”), when balance of forces is formed by the forces of inertia, the surplus pressure, the centrifugal force, the Coriolis force and the force of wave resistance due to the internal wave radiation; the Coriolis force is a key factor supporting and keeping compact the anti-cyclonic LMW, the Meddies; it prevents the LMWs from breakup, limits their geometrical dimensions, affects the lens angular velocity variations. The cyclonic LMWs are destabilized by the Coriolis force, getting small thickness and under certain conditions may disappear as a density anomaly already at this stage;
2) the viscid stage (“old lens”) is characterized by a slow decreasing of the LMW thickness up to its limit value, that is determined by the LMW initial thickness, the initial LMW stratification as well as ambient stratification; during the final period of the viscous stage the exchange of heat and salinity with ambient water-mass may, on a characteristic temporal scales about a year, significantly influence on the degenerations of the LMW as a density anomaly; at this stage the anti-cyclonic LMW, the Meddy, continues to have the anti-cyclonic rotation.

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