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1.
The Climatic variability of the seasonal water exchange in the Strait of Gibraltar and the spatial structure of the tongue of the Mediterranean Waters (MW) in the Atlantic Ocean are studied. The analysis is based on the results of a numerical experiment using a 3D ocean circulation model developed at the Institute of Computational Mathematics (ICM RAS) with a resolution of the dataset over the latitude and longitude equal to 0.25 degree. The seasonal evolution of the salinity and density fields is calculated in the North Atlantic (from 20 °S, including the Mediterranean Sea) and in the Arctic Ocean (including the Bering Sea). The comparison of the model estimates with the results of field observations demonstrated good agreement. The transport of the MW into the Atlantic is close to the observed data (during the year, it varies from 1.8 Sv in the winter to 0.9 Sv in the summer). The complex pattern of the currents in the region of the MW spreading is confirmed. The alternating character of the saline MW tongue at the 1000-m level is shown for the first time. It is found that the zones of maximum salinities in the open part of the ocean coincide with the main trajectories of migration of MW lenses and the regions of their decomposition. 相似文献
2.
Synoptic sea surface temperature anomalies (SSTAs) were determined as a result of separation of time scales smaller than 183 days. The SSTAs were investigated using daily data of ocean weather station “C” (52.75°N; 35.5°W) from 1 January 1976 to 31 December 1980 (1827 days). There were 47 positive and 50 negative significant SSTAs (lifetime longer than 3 days, absolute value greater than 0.10 °C) with four main intervals of the lifetime repetitions: 1. 4–7 days (45% of all cases), 2. 9–13 days (20-25%), 3. 14–18 days (10-15%), and 4. 21–30 days (10-15%) and with a magnitude 1.5-2.0 °C. An upper layer balance model based on equations for temperature, salinity, mechanical energy (with advanced parametrization), state (density), and drift currents was used to simulate SSTA. The original method of modelling taking into account the mean observed temperature profiles proved to be very stable. The model SSTAs are in a good agreement with the observed amplitudes and phases of synoptic SSTAs during all 5 years. Surface heat flux anomalies are the main source of SSTAs. The influence of anomalous drift heat advection is about 30-50% of the SSTA, and the influence of salinity anomalies is about 10-25% and less. The influence of a large-scale ocean front was isolated only once in February-April 1978 during all 5 years. Synoptic SSTAs develop just in the upper half of the homogeneous layer at each winter. We suggest that there are two main causes of such active sublayer formation: 1. surface heat flux in the warm sectors of cyclones and 2. predominant heat transport by ocean currents from the south. All frequency functions of the ocean temperature synoptic response to heat and momentum surface fluxes are of integral character (red noise), though there is strong resonance with 20-days period of wind-driven horizontal heat advection with mixed layer temperature; there are some other peculiarities on the time scales from 5.5 to 13 days. Observed and modelled frequency functions seem to be in good agreement. 相似文献
3.
Numerical experiments with the circulation model of the North Atlantic based on the splitting algorithms in the σ-coordinate system with a spatial resolution allowing for reproducing synoptic eddies were performed in two versions: with the Arctic Ocean and without it (boundary along 78°N). They showed that the account for the water exchange with the Arctic is fundamentally important for reproducing jet dynamics at the western boundary of the Atlantic down to the subtropical zone. The influence of the conditions at the liquid boundary that separates the Atlantic and the Arctic extends not only over the subarctic area [29] but is also “transferred” by the Labrador Current and the Slope Water Current (SWC) to the area of the Gulf Stream proper. One cannot properly describe the detachment of the Gulf Stream from the coast without adequate reproducing of the Labrador Current and SWC. An hypothesis is posed that the location of the detachment region at 35°N is caused by strong vertical motions at the interface between the SWC and the Gulf Stream jet with horizontal velocities that are almost equal to those at the exit from the Florida Strait. A comparison of the model circulation with that retrieved from the hydrological data and the drift of neutral buoyancy floats [14, 22] showed both qualitative and quantitative coincidences of the features of the northward warm water transfer such as the streamline around the so-called northwestern “corner” (motion “along the topography”) and the jet-wise transport of these waters from Labrador to the northeast inside a kind of “pipeline,” which is limited in the upper baroclinic layer 1 km thick by mean velocity contour lines of about 10 cm/s. A comparison between the experimental [19] and model fields of the ocean level showed that, at the absence of direct representation of the water (mass) exchange between the Atlantic and the Arctic Ocean, the decrease of the gradient velocities in the Gulf Stream may reach 30%. 相似文献
4.
The goal of this paper is to present some results on the monsoon circulation in the Indian Ocean simulated with a σ-coordinate ocean model developed at the Institute of Numerical Mathematics, RAS. The model has a horizontal resolution of (1/8)° × (1/12)° and contains 21 σ-layers of uneven thickness. Realistic bottom topography and land geometry are used. The numerical experiments were carried out for 15 years starting from the Levitus climatology for January and monthly mean climatic atmospheric forcing from the NCEP reanalysis data. The annual cycle of the surface and subsurface currents and temperature and salinity fields were analyzed. The model reproduces well the Summer Monsoon and the Winter Monsoon currents and their time evolution and spatial structures. The Somali Current is adequately modeled. During the Summer Monsoon, the velocities of the current exceed 2 m/s, while the total mass transport is approximately 70 Sv. The model results show that a reversal of the Somali Current from the northern direction in the summer to the southern direction in the winter is accompanied by the generation of anticyclonic eddies, which drift westward owing to the β-effect and dissipate either near the Somali shore or in the Gulf of Aden. The monsoon variability of the equatorial surface current and equatorial subsurface countercurrent system are analyzed. It is shown that these currents are generated predominantly by the zonal component of wind stress, in which the half-year harmonic dominates. This leads to the fact that the equatorial surface current also changes its direction with a half-year periodicity almost in phase with the wind. The oppositely directed subsurface compensational countercurrent changes its direction with a time lag of approximately one month. Gradient currents, which appear in the Bay of Bengal due to the riverine runoff, make an important contribution to the circulation. This effect manifests itself especially strongly in the summer during the peak of the Ganges River runoff, which transports fresh turbid waters. The principal features of the large-scale quasi-stationary gyre structure of the Indian Ocean such as the Great Whirl, Socotra high, and Laccadive high and low are simulated. 相似文献
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6.
B. N. Filyushkin S. N. Moshonkin S. A. Myslenkov V. B. Zalesnyi N. G. Kozhelupova 《Oceanology》2013,53(6):643-654
The character of the water exchange in the Denmark Strait for the period of 1958–2006 is studied based on the results of the numerical experiments using the model of the ocean circulation developed at the Institute of Numerical Mathematics of the Russian Academy of Sciences with a resolution of 0.25 degrees in latitude and longitude with 27 vertical levels. The calculations were performed for the North Atlantic area from 30° S, including the Arctic Ocean and the Bering Sea. The width of the Denmark Strait at 66° N is about 650 km, and the depth is approximately 550 m. The fields of the temperature, salinity, and density and the components of the current velocities were simulated. In this period, the average overflow of dense waters with the conventional potential density σ0 > 27.80 to the North Atlantic through the Denmark Strait was 1.86 ± 0.96 Sv, and, for the nearbottom and intermediate waters with σ0 > 27.50, it was 3.84 ± 1.31 Sv. The maximum values of the overflow transport through the strait were recorded in 1962, 1972, 1983, 1990, and 2000. Exactly these years showed the highest values of the North Atlantic oscillation (NAO) index. This fact confirms the domination of the decadal variability of the hydrogeological processes in the North Atlantic. The model section of the current velocity through the strait showed the occurrence of at least four well marked jets that vertically occupy the entire sectional area from the surface to the bottom. The two jets divided by a northward jet at the strait’s middle move southward along the Greenland slope. The northward current along Iceland is also identified. This structure of the currents is also supported by the analysis of the observed variability of the absolute topography of the ocean’s surface. 相似文献
7.
The problem of simulating sea dynamics in areas comprising near-shore zones and zones of high turbulence is considered. A mathematical model and the numerical algorithm of its solving are formulated. The model is based on the equations for nonhydrostatic dynamics and includes (k-ε) and (k-ω) parameterization of turbulent processes. The equations of the model are written in a σ-coordinate system. The numerical algorithm for solving the problem is based on the use of implicit schemes owing to the splitting with respect to the physical processes and space coordinates. The model calculations were performed for four nested sea basins with different spatial resolution: the Baltic Sea (3.7-km space resolution), the Gulf of Finland (1.85-km resolution), the Tallinn-Helsinki area (560-m resolution), and Tallinn Bay (93-m resolution). The results of the experiment show that the model well simulates the processes of enhanced turbulent activity in the near-shore zones that affect the local features of the sea characteristics. 相似文献
8.
S. N. Moshonkin A. V. Gusev V. B. Zalesny V. I. Byshev 《Izvestiya Atmospheric and Oceanic Physics》2016,52(2):196-206
Results of numerical experiments with an eddy-permitting ocean circulation model on the simulation of the climatic variability of the North Atlantic and the Arctic Ocean are analyzed. We compare the ocean simulation quality with using different subgrid mixing parameterizations. The circulation model is found to be sensitive to a mixing parametrization. The computation of viscosity and diffusivity coefficients by an original splitting algorithm of the evolution equations for turbulence characteristics is found to be as efficient as traditional Monin–Obukhov parameterizations. At the same time, however, the variability of ocean climate characteristics is simulated more adequately. The simulation of salinity fields in the entire study region improves most significantly. Turbulent processes have a large effect on the circulation in the long-term through changes in the density fields. The velocity fields in the Gulf Stream and in the entire North Atlantic Subpolar Cyclonic Gyre are reproduced more realistically. The surface level height in the Arctic Basin is simulated more faithfully, marking the Beaufort Gyre better. The use of the Prandtl number as a function of the Richardson number improves the quality of ocean modeling. 相似文献
9.
S. N. Moshonkin V. B. Zalesny A. V. Gusev 《Izvestiya Atmospheric and Oceanic Physics》2018,54(5):495-506
The algorithm for splitting k–ω turbulence equations is used to parameterize viscosity and diffusion coefficients in the ocean general circulation model. The k–ω equations are split into stages describing the transport-diffusion and generation-dissipation of the turbulent kinetic energy and frequency function ω. At the generation-dissipation stage, the equations are solved analytically. Calculations of circulation in the North Atlantic–Arctic Ocean for 1948–2009 have been carried out. The experiments demonstrate an adequate reproduction of hydrophysical characteristics and high efficiency of the algorithm. It is shown that considering the climatic annual mean buoyancy frequency in the turbulence equations at the generation-dissipation stage is an important factor in improving the accuracy of simulated fields. 相似文献
10.
S. N. Moshonkin G. V. Alekseev N. A. Dianskii A. V. Gusev V. B. Zalesny 《Izvestiya Atmospheric and Oceanic Physics》2011,47(5):628-641
Calculations were performed using a model of the combined circulation of the Atlantic Ocean (from 20° S), the Arctic Ocean, and the Bering Sea with a resolution of 0.25° by latitude and longitude for 1958–2006. The results are compared with observational data and results obtained by other models. Model estimates were obtained for the evolution of the Atlantic water inflow into the Arctic basin through the Fram Strait and the Barents Sea. Increased transports of Atlantic water inflow into the Arctic basin were found for the first half of the 1990s and 2004–2006. The relation between Atlantic water transports into the Arctic basin and variations in the North Atlantic oscillation is shown. A positive trend of Atlantic water inflow into the Arctic basin through the Fram Strait (0.061 Sv per year) was revealed. The evolution of the freshwater-layer thickness in the Beaufort Circulation (BC) is considered. There are three periods of its increased values combined with the increased anticyclonic vorticity of BC currents: the 1960s, the 1980s, and from 1999 until now. The model estimate for a statistical mean timescale of the cycle of freshwater concentration and sink from the BC is 16 years, which is close to currently existing estimates. The evolution of anticyclonic vorticity of currents leads the variations in the freshwater-layer thickness of the BC by 1.75 years. Since the mid-1970s, there have been long positive trends of both the freshwater-layer thickness and anticyclonic vorticity of currents in the BC. In the same time period, there has been a satellite-registered negative trend in the ice area in the Arctic, which was reproduced by the model. 相似文献