المؤلفون: D. Sidorenko, S. Danilov, J. Streffing, V. Fofonova, H. F. Goessling, P. Scholz, Q. Wang, A. Androsov, W. Cabos, S. Juricke, N. Koldunov, T. Rackow, D. V. Sein, T. Jung

المصدر: Journal of Advances in Modeling Earth Systems, Vol 13, Iss 10, Pp n/a-n/a (2021)

مصطلحات موضوعية: AMOC variability, density framework, climate models, Physical geography, GB3-5030, Oceanography, GC1-1581

الوصف: Abstract Using the depth (z) and density (ϱ) frameworks, we analyze local contributions to AMOC variability in a 900‐year simulation with the AWI climate model. Both frameworks reveal a consistent interdecadal variability; however, the correlation between their maxima deteriorates on year‐to‐year scales. We demonstrate the utility of analyzing the spatial patterns of sinking and diapycnal transformations through depth levels and isopycnals. The success of this analysis relies on the spatial binning of these maps which is especially crucial for the maps of vertical velocities which appear to be too noisy in the main regions of upwelling and downwelling because of stepwise bottom topography. Furthermore, we show that the AMOC responds to fast (annual or faster) fluctuations in atmospheric forcing associated with the NAO. This response is more obvious in the ϱ than in the z framework. In contrast, the link between AMOC and deep water production south of Greenland is found for slower fluctuations and is consistent between the frameworks.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1942-2466Test

الوصول الحر: https://doaj.org/article/3a840b292a25436d94cfc021fa87c44dTest

المؤلفون: S. Juricke, S. Danilov, N. Koldunov, M. Oliver, D. V. Sein, D. Sidorenko, Q. Wang

المصدر: Journal of Advances in Modeling Earth Systems, Vol 12, Iss 12, Pp n/a-n/a (2020)

مصطلحات موضوعية: kinetic energy backscatter, viscosity closures, mesoscale eddies, ocean modeling, eddy‐permitting resolution, overdissipation, Physical geography, GB3-5030, Oceanography, GC1-1581

الوصف: Abstract Ocean models at eddy‐permitting resolution are generally overdissipative, damping the intensity of the mesoscale eddy field. To reduce overdissipation, we propose a simplified, kinematic energy backscatter parametrization built into the viscosity operator in conjunction with a new flow‐dependent coefficient of viscosity based on nearest neighbor velocity differences. The new scheme mitigates excessive dissipation of energy and improves global ocean simulations at eddy‐permitting resolution. We find that kinematic backscatter substantially raises simulated eddy kinetic energy, similar to an alternative, previously proposed dynamic backscatter parametrization. While dynamic backscatter is scale‐aware and energetically more consistent, its implementation is more complex. Furthermore, it turns out to be computationally more expensive, as it applies, among other things, an additional prognostic subgrid energy equation. The kinematic backscatter proposed here, by contrast, comes at no additional computational cost, following the principle of simplicity. Our primary focus is the discretization on triangular unstructured meshes with cell placement of velocities (an analog of B‐grids), as employed by the Finite‐volumE Sea ice‐Ocean Model (FESOM2). The kinematic backscatter scheme with the new viscosity coefficient is implemented in FESOM2 and tested in the simplified geometry of a zonally reentrant channel as well as in a global ocean simulation on a 1/4° mesh. This first version of the new kinematic backscatter needs to be tuned to the specific resolution regime of the simulation. However, the tuning relies on a single parameter, emphasizing the overall practicality of the approach.

وصف الملف: electronic resource

العلاقة: https://doaj.org/toc/1942-2466Test

الوصول الحر: https://doaj.org/article/cf765c74416b485482fcceeb2f3717e0Test