Numerical modeling of ocean hydrodynamics with variational assimilation of observational data

Models and methods of the numerical modeling of ocean hydrodynamics dating back to the pioneering works of A.S. Sarkisyan are considered, with emphasis on the formulation of problems and algorithms of mathematical modeling and the four-dimensional variational assimilation of observational data. An algorithm is proposed for studying the sensitivity of the optimal solution to observational data errors in a seasurface temperature assimilation problem in order to retrieve heat fluxes on the surface. An example of a solution of the optimal problem of the World Ocean hydrodynamics with the assimilation of climatic temperature and salinity observations is offered.     

Sub-inertial oscillations in the Black Sea generated by the semidiurnal tidal potential

The Black Sea shelf is a region of intense manifestation of various dynamical processes. Under the influence of different natural forces, eddy-wave phenomena develop here, which influence the general circulation of sea waters, biological productivity, and the condition of the engineering structures. Modern numerical models allow us to simulate and analyze the processes of the joint dynamics of marine circulation and large-scale waves. In this work, we study the spatiotemporal spectral characteristics of the sea level and velocity fluctuations formed due to atmospheric forcing and tidal potential. The hydrophysical fields are calculated using the Institute of Numerical Mathematics, Russian Academy of Sciences (INM RAS), σ model based on primitive equations. We use the CORE data as atmospheric forcing at the sea surface; the tidal potential is described by the semidiurnal lunar constituent M₂. Analyzing the simulation results makes it possible to emphasize that accounting for the semidiurnal tidal potential not only improves the accuracy of the sea-level calculation at coastal stations, but also generates subinertial baroclinic oscillations previously found in the Black Sea from the data of in situ observations.     

A method of oceanographic data assimilation based on the theory of optimal control

Fundamental points of the computational procedure for the assimilation of observations by a model for a large-scale ocean circulation are discussed.Translated by Vladimir A. Puchkin.     

Splitting Numerical Technique with Application to the High Resolution Simulation of the Indian Ocean Circulation

The aim of this paper is twofold : To present an efficient numerical technique for the simulation of the ocean general circulation (OGC) and to apply it to the simulation of the Indian Ocean dynamics with high spatial resolution. To solve model equations we use the splitting method by physical processes and space coordinates. We select the main parts of the model operator and then perform their numerical treatment independently of one another. We describe the general methodology and some special aspects of this approach. Numerical treatment of the monsoon circulation is performed on the basis of the sigma-coordinate primitive equation model, which was developed at the Institute of Numerical Mathematics (Moscow, Russia). We present and briefly analyze the results of the numerical experiment with high spatial resolution 1/8° along latitude, 1/12° along longitude, and with 21 vertical sigma levels.The work was supported by the Russian Foundation for the Basic Research (03-05-64354, 02-05-64909) and by the Russian Academy of Sciences (10002-251/OMN-03/026-020/240603-807)     

Variational Data Assimilation in Problems of Modeling Hydrophysical Fields in Open Water Areas

Izvestiya, Atmospheric and Oceanic Physics - The formulation of boundary conditions at liquid (open) boundaries is a topical problem in mathematically modeling the hydrothermodynamics of open water...     

Data-computing technologies: A new stage in the development of operational oceanography

An analysis is given of the methods of operational oceanography based on measurements derived from satellite data, observations acquired by drifters and passing vessels, and modern simulations of marine and oceanic circulations. In addition, a historical review is conducted of the previous and current research in this field carried out in the Soviet Union, Ukraine, and Russia. A discussion is given of the principles underlying the design of an effective data-computing system (DCS) for solving the problems of operational oceanography and the implementation of the prototype system for the Black Sea within the joint research project of the Russian Academy of Sciences (RAS) and the National Academy of Sciences of Ukraine (NASU) “The Black Sea as an Ocean Simulation Model.” The effectiveness of applying the multicomponent splitting method in the construction of sea circulation models and specialized DCSs with integrated algorithms of variational assimilation of observational data is estimated. The concept of using the Black Sea as a testing site for innovations is developed. The underlying idea of the concept is the similarity of the Black Sea dynamics with processes in the oceans. The numerical Black Sea circulation models used in the project are described, their development areas are discussed, and the requirements to a Black Sea observing system are defined.     

High resolution modeling of the monsoon circulation in the Indian Ocean

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.     

Interdecadal variability of water thermal structure in the North Atlantic Region and its climatic significance

Doklady Earth Sciences -     

Variational Data Assimilation Technique in Mathematical Modeling of Ocean Dynamics

Problems of the variational data assimilation for the primitive equation ocean model constructed at the Institute of Numerical Mathematics, Russian Academy of Sciences are considered. The model has a flexible computational structure and consists of two parts: a forward prognostic model, and its adjoint analog. The numerical algorithm for the forward and adjoint models is constructed based on the method of multicomponent splitting. The method includes splitting with respect to physical processes and space coordinates. Numerical experiments are performed with the use of the Indian Ocean and the World Ocean as examples. These numerical examples support the theoretical conclusions and demonstrate the rationality of the approach using an ocean dynamics model with an observed data assimilation procedure.