Horizontal Ocean Circulation Research Articles

Modeling the influence of the Earth rotation axis position on the global climate variations

This study presents the results of numerical experiments to determine the Earth’s climate when its rotation axis is displaced without changing the axis tilt to the ecliptic plane. There is some evidence of the possibility of this shift in the past. The calculations were carried out using a hydrodynamic three-dimensional global climate model, including blocks of atmosphere, thermohaline large-scale ocean circulation and sea ice. Numerical experiments demonstrate a significant temperature changes throughout the world. A large area of Antarctica warmed up to temperatures above 15 ° C. This is reason of intense melting of glaciers for a long time. Significant warming of the Arctic Ocean will lead to sea ice melting in the Arctic. Strong changes in temperature and ice cover lead to significant changes in horizontal ocean circulation. A procedure is proposed for calculating wind speed in atmosphere energy - moisture balance model. It is based on the geostrophic approach, taking into account the thermal component of the wind, and introducing the mechanism of friction on the underlying surface. A technique has been developed for the formation of the necessary maps and the relationships between them when turning the Earth rotation axis or using new cartographic data.

High atmospheric horizontal resolution eliminates the wind‐driven coastal warm bias in the southeastern tropical Atlantic

AbstractWe investigate the strong warm bias in sea surface temperatures (SST) of the southeastern tropical Atlantic that occurs in most of the current global climate models. We analyze this bias in the Max Planck Institute Earth System Model at different horizontal resolutions ranging from 0.1° to 0.4° in the ocean and 0.5° to 1.8° in the atmosphere. High atmospheric horizontal resolution eliminates the SST bias close to the African coast, due to an improved representation of surface wind stress near the coast. This improvement affects coastal upwelling and horizontal ocean circulation, as confirmed with dedicated sensitivity experiments. The wind stress improvements are partly caused by the better represented orography at higher horizontal resolution in the spectral atmospheric model. The reductions of the coastal SST bias obtained through higher horizontal resolution do not, however, translate to a reduction of the large‐scale bias extending westward from the African coast into the southeastern tropical Atlantic.

Hydraulic Characteristics of Horizontal Sea Water Exchange Block

In this study, hydraulic characteristics of horizontal ocean circulation block was examined through hydraulic experiments. Hydraulic experiments including 12 wave cases, 5 current cases and 60 wave-current cases were carried out to propose useful empirical formula. Outgoing current speed is increased as the wave height higher rather than wave period under the wave only condition. The water level at the front of the water circulation block is going up and going down at the rear side under the current only condition.

The modelling of the toroidal magnetic field induced by tidal ocean circulation

Observations of the ocean-induced magnetic field by the CHAMP magnetic space mission have the potential to be used as a constraint when examining ocean dynamics. This has initiated theoretical studies on the prediction of the poloidal magnetic field induced by the horizontal ocean-circulation flow. This study deals with the computation and analysis of the toroidal magnetic field induced by the tidal ocean-circulation flow on the background of the main Earth′s geomagnetic field. Since the induced toroidal magnetic field cannot be modelled by the single-layer approximation model used to predict the poloidal magnetic field, we treat the ocean as a spherical layer of a finite thickness and compute the toroidal magnetic field by a matrix-propagator technique with a source of electric currents in the ocean layer. Our numerical simulations based on the OMCT tidal ocean velocities show that the induced toroidal magnetic field is extremely sensitive to the vertical gradient of horizontal ocean flow. The larger this gradient, the stronger the induced toroidal magnetic field. Specifically, its magnitudes vary from 10−2 nT for barotropic flow to several nT for baroclinic flow. We show that the induced toroidal magnetic field generated by M2 tidal forcing is comparable in amplitude to the induced poloidal part of the field. The induced toroidal and poloidal magnetic fields differ, however, in their spatial behaviour.

Stochastically-driven multidecadal variability of the Atlantic meridional overturning circulation in CCSM3

The Atlantic meridional overturning circulation (AMOC) in the last 250 years of the 700-year-long present-day control integration of the Community Climate System Model version 3 with T85 atmospheric resolution exhibits a red noise-like irregular multi-decadal variability with a persistence longer than 10 years, which markedly contrasts with the preceding ~300 years of very regular and stronger AMOC variability with ~20 year periodicity. The red noise-like multi-decadal AMOC variability is primarily forced by the surface fluxes associated with stochastic changes in the North Atlantic Oscillation (NAO) that intensify and shift northward the deep convection in the Labrador Sea. However, the persistence of the AMOC and the associated oceanic anomalies that are directly forced by the NAO forcing does not exceed about 5 years. The additional persistence originates from anomalous horizontal advection and vertical mixing, which generate density anomalies on the continental shelf along the eastern boundary of the subpolar gyre. These anomalies are subsequently advected by the mean boundary current into the northern part of the Labrador Sea convection region, reinforcing the density changes directly forced by the NAO. As no evidence was found of a clear two-way coupling with the atmosphere, the multi-decadal AMOC variability in the last 250 years of the integration is an ocean-only response to stochastic NAO forcing with a delayed positive feedback caused by the changes in the horizontal ocean circulation.

Reversed North Atlantic gyre dynamics in present and glacial climates

The dynamics of the North Atlantic subpolar gyre (SPG) are assessed under present and glacial boundary conditions by investigating the SPG sensitivity to surface wind-stress changes in a coupled climate model. To this end, the gyre transport is decomposed in Ekman, thermohaline, and bottom transports. Surface wind-stress variations are found to play an important indirect role in SPG dynamics through their effect on water-mass densities. Our results suggest the existence of two dynamically distinct regimes of the SPG, depending on the absence or presence of deep water formation (DWF) in the Nordic Seas and a vigorous Greenland–Scotland ridge (GSR) overflow. In the first regime, the GSR overflow is weak and the SPG strength increases with wind-stress as a result of enhanced outcropping of isopycnals in the centre of the SPG. As soon as a vigorous GSR overflow is established, its associated positive density anomalies on the southern GSR slope reduce the SPG strength. This has implications for past glacial abrupt climate changes, insofar as these can be explained through latitudinal shifts in North Atlantic DWF sites and strengthening of the North Atlantic current. Regardless of the ultimate trigger, an abrupt shift of DWF into the Nordic Seas could result both in a drastic reduction of the SPG strength and a sudden reversal in its sensitivity to wind-stress variations. Our results could provide insight into changes in the horizontal ocean circulation during abrupt glacial climate changes, which have been largely neglected up to now in model studies.

Horizontal Ocean Circulation Forced by Deep-Water Formation. Part I: An Analytical Study

The horizontal ocean circulation generated by vertical convection is investigated analytically. The stratification is parameterized by a two-layer ocean and attention is focused on the spinup phase when the phenomena can be considered as linear. It is found that the response of the ocean to a two-dimensional idealized thermohaline forcing is baroclinic. A cyclonic gyre is generated in the upper layer, an anticyclonic gyre in the lower layer. Variation of the Coriolis parameter with latitude causes the center of the gyre to drift westward at the speed of long baroclinic Rossby waves.

Horizontal Ocean Circulation Forced by Deep-Water Formation. Part II: A Quasi-geostrophic Simulation

This numerical experiment aims to investigate the dynamical effects of the vertical convection of waters, occurring in regions where the cooling of the upper ocean is due to periodical, local, rough winter atmospheric conditions. The simulation is performed with a 2-layer quasi-geostrophic model, which configuration yields a small internal radius of deformation (10 km), and a high spatial resolution (5 km). The sinking of waters is parametrized by a conversion, in a limited area, of some of the upper-layer fluid into lower-layer fluid. This forcing is continuously active for the first 3 months of the year and is zero otherwise. This cycle is repeated for several years. The model response results in an elevation of the interface (a dome), which generates a geostrophic circulation first limited to the region where the forcing is active. The dome grows and reaches a critical amplitude where it becomes baroclinically unstable, and breaks into eddies of smaller size, in a way very comparable to what happens in experiments done in a rotating tank. After 15 forcing cycles, a general circulation is established to the whole basin, with mean and eddy currents in statistical equilibrium. Eddy-driven mean flows are then superposed on, and interact with, the geostrophic circulation due to the mean signature of the dome. The eddy currents are mostly generated by the baroclinic instability of the dome, but also by the barotropic (horizontal shear) instability of the mean currents. The oceanic relevance of the experiment is discussed in the context of the Western Mediterranean Sea, with some success for the upper-layer circulation.