Search

The classic baroclinic, wind-driven, double gyre problem is considered over a range of deformation radii, wind stress amplitudes, and bottom friction coefficients with the aim of better understanding the transfer of energy across scales. In this β-plane basin setting, significant differences are found with respect to classic studies of geostrophic turbulence, which generally assume zonal periodicity and for which the β term does not play a direct role in the energy transfers. In a basin geometry, the β term can play a direct role in the transfers; for example, it can be the dominant term allowing for energy transfer between the basin scale and the baroclinic mesoscale. It is also found that barotropization of baroclinic energy forces the barotropic mode near scales at which bottom drag damps this mode. Associated with this, the barotropic, nonlinear, inverse energy cascade does not extend between mesoscale injection and large-scale dissipation wavenumbers, as is often assumed. Instead, it is part of a 'double cascade' of barotropic energy in which the nonlinear inverse cascade is nearly offset by a forward cascade associated with the β term. This is particularly evident in weak bottom drag simulations, for which a time eddy-mean decomposition of the flow reveals the double cascade to be associated with the eddy-only terms. [ABSTRACT FROM AUTHOR]

Highlights: [•] Conducted an ensemble-based DA study using POP OGCM & DART. [•] Proposed a new inflation scheme and studied it in a low-order model. [•] A variety of diagnostics demonstrates improved DA performance. [•] Assimilated state shows decreased SST error and subsurface temperature errors. [•] Hindcast skill demonstrated on initialization with assimilated state. [Copyright &y& Elsevier]

Abstract: On the decadal to centennial time scale, changes in climate are controlled strongly by changes in ocean circulation. However, because of limitations inherent to the time integration schemes used in present-day ocean models, state-of-the-art climate change simulations resolve the oceans only very coarsely. With an aim to enable long-term simulations of ocean circulation at the high resolutions required for a better representation of global ocean dynamics, we have implemented fully-implicit time integration schemes in a version of the popular ocean general circulation model POP (Parallel Ocean Program), employing Jacobian-free Newton–Krylov techniques. Here, we describe the numerical principles underlying iPOP in some detail and present a few computational results. While there are many advantages to this approach, including a consistent and uniform treatment of the terms in the governing equations, the primary advantage lies in the ability to take time steps that are of relevance to the physical phenomenon that is being studied. The time step is not limited (for stability reasons) by the fastest modes of the system. [Copyright &y& Elsevier]

Examines the dynamics of an idealized double-gyre circulation model in an ocean basin. Focus on the variability of ocean circulations; Importance of considering global bifurcations of the circulation; Identification of a complicated global bifurcation phenomenon known as the Shilkinov phenomenon.