Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

Barnier, Bernard; Akuetevi, Cataria Quam Cyrille; Verron, Jacques; Molines, Jean Marc; Lecointre, Albanne

doi:10.5194/osd-12-735-2015

Cited by 4 publications

(3 citation statements)

References 34 publications

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“…9). In observations (called "flanking cyclones" by Beal and Donohue (2013)) and a fineresolution ocean general circulation model (Akuetevi et al, 2015) bursts are seen to lead to the substantial upwelling of cold and nutrient rich water masses from the deep. The dipoles transport these water masses offshore, leading to an increased biological production several hundreds of kilometers from the coast (Kawamiya and Oschlies, 2003;Wirth et al, 2001).…”

Section: Discussionmentioning

confidence: 99%

Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

Akuetevi

Wirth

2015

Ocean Sci.

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Abstract. The dynamics of low latitude turbulent westernboundary currents (WBCs) crossing the Equator are considered using numerical results from integrations of a reduced-gravity shallow-water model. For viscosity values of 1000 m 2 s −1 and greater, the boundary layer dynamics compares well to the analytical Munk-layer solution. When the viscosity is reduced, the boundary layer becomes turbulent and coherent structures in the form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer, VSL) and dipoles appear. Three distinct boundary layers emerge, the VSL, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity; the second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. Characteristic scales of the dynamics and dissipation are determined.A pragmatic approach to determine the eddy viscosity diagnostically for coarse-resolution numerical models is proposed.

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Section: Discussionmentioning

confidence: 99%

Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

Akuetevi

Wirth

2015

Ocean Sci.

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Section: Discussionmentioning

confidence: 99%

“…It has been shown in engineering fluid dynamics that boundary-layer dynamics involves different types of coherent structures (see, e.g., Aubry et al, 1988;Robinson, 1991). In satellite observations of the SC, small flanking cyclones correlated with the large anticyclone tend to circulate clockwise around it (Beal and Donohue, 2013).…”

Section: Introductionmentioning

confidence: 99%

Dynamics of turbulent western boundary currents at low latitude in a shallow water model

Akuetevi

Wirth

2014

Preprint

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Abstract. The dynamics of low latitude turbulent western boundary currents, subject to two different types of idealized wind forcing, Monsoon Wind and Trade Wind, is considered using numerical results from integrations of a reduced gravity shallow-water model. For viscosity values of 1000 m2 s−1 and above, the boundary layer dynamics compares well to the analytical solutions of the Munk-layer and the inertial-layer, derived from quasigeostrophic theory. Modifications due to variations in the layer thickness (vortex stretching) are only important close to the boundary. When the viscosity is reduced the boundary layer becomes turbulent and coherent structures in form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer) and dipoles appear. Three distinct boundary layers emerge, the viscous sub-layer, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vorticity balance between the viscous transport and the advective transport of vorticity. The second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. A pragmatic approach to determine the eddy viscosity diagnostically for coarse resolution numerical models is proposed.

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Benefits of Increasing the Model Resolution for the Seasonal Forecast Quality in EC-Earth

et al. 2016

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Resolution in climate models is thought to be an important factor for advancing seasonal prediction capability. To test this hypothesis, seasonal ensemble reforecasts are conducted over 1993-2009 with the European community model EC-Earth in three configurations: standard resolution (;18 and ;60 km in the ocean and atmosphere models, respectively), intermediate resolution (;0.258 and ;60 km), and high resolution (;0.258 and ;39 km), the two latter configurations being used without any specific tuning. The model systematic biases of 2-m temperature, sea surface temperature (SST), and wind speed are generally reduced. Notably, the tropical Pacific cold tongue bias is significantly reduced, the Somali upwelling is better represented, and excessive precipitation over the Indian Ocean and over the Maritime Continent is decreased. In terms of skill, tropical SSTs and precipitation are better reforecasted in the Pacific and the Indian Oceans at higher resolutions. In particular, the Indian monsoon is better predicted. Improvements are more difficult to detect at middle and high latitudes. Still, a slight improvement is found in the prediction of the winter North Atlantic Oscillation (NAO) along with a more realistic representation of atmospheric blocking. The sea ice extent bias is unchanged, but the skill of the reforecasts increases in some cases, such as in summer for the pan-Arctic sea ice. All these results emphasize the idea that the resolution increase is an essential feature for forecast system development. At the same time, resolution alone cannot tackle all the forecast system deficiencies and will have to be implemented alongside new physical improvements to significantly push the boundaries of seasonal prediction.

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Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

Cited by 4 publications

References 34 publications

Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

Dynamics of turbulent western boundary currents at low latitude in a shallow water model

Benefits of Increasing the Model Resolution for the Seasonal Forecast Quality in EC-Earth

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