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  • Author or Editor: Jinqiao Duan x
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Jinqiao Duan
and
Stephen Wiggins

Abstract

In this paper, the motion of fluid parcels in the two-dimensional kinematic model of a meandering jet developed by Bower and Samelson is studied. The earlier work is extended by considering quasiperiodic spatiotemporal variability in a reference frame moving with the phase speed of the meander. This necessitates the introduction of recently developed techniques in dynamical systems theory for analyzing transport in velocity fields with quasiperiodic variability.

A detailed comparison between exchange for variability with one and two independent frequencies is given, and it is shown that the exchange rates may be very different for periodic and quasiperiodic variability.

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Tamay M. Özgökmen
,
Paul F. Fischer
,
Jinqiao Duan
, and
Traian Iliescu

Abstract

Overflows are bottom gravity currents that supply dense water masses generated in high-latitude and marginal seas into the general circulation. Oceanic observations have revealed that mixing of overflows with ambient water masses takes place over small spatial and time scales. Studies with ocean general circulation models indicate that the strength of the thermohaline circulation is strongly sensitive to representation of overflows in these models. In light of these results, overflow-induced mixing emerges as one of the prominent oceanic processes. In this study, as a continuation of an effort to develop appropriate process models for overflows, nonhydrostatic 3D simulations of bottom gravity are carried out that would complement analysis of dedicated observations and large-scale ocean modeling. A parallel high-order spectral-element Navier–Stokes solver is used as the basis of the simulations. Numerical experiments are conducted in an idealized setting focusing on the startup phase of a dense water mass released at the top of a sloping wedge. Results from 3D experiments are compared with results from 2D experiments and laboratory experiments, based on propagation speed of the density front, growth rate of the characteristic head at the leading edge, turbulent overturning length scales, and entrainment parameters. Results from 3D experiments are found to be in general agreement with those from laboratory tank experiments. In 2D simulations, the propagation speed is approximately 20% slower than that of the 3D experiments and the head growth rate is 3 times as large, Thorpe scales are 1.3–1.5 times as large, and the entrainment parameter is up to 2 times as large as those in the 3D experiments. The differences between 2D and 3D simulations are entirely due to internal factors associated with the truncation of the Navier–Stokes equations for 2D approximation.

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