Assessment of the effectiveness of POLYMODE data assimilation by a numerical barotropic model for synoptic motions

This paper considers the results of numerical experiments involving POLYMODE data assimilation by a barotropic model for synoptic ocean dynamics. The model's response the data assimilation for various space-time discretenesses of assimilation is studied. Results derived from the application of optimal interpolation algorithms and modified optimal filtration algorithms are compared. Qualitative similarity to the calculations carried out through the simulation modelling technique is noted. Optimal assimilation algorithms are determined, depending on the space-time discreteness used. An optimal sampling discreteness for the POLYMODE conditions is suggested.Translated by Vladimir A. Puchkin.     

Four-dimensional analysis of the variability of hydrophysical fields in the tropical atlantic and on the shelf of guinea

The problem of monitoring of the mesoscale variability of hydrophysical fields in the shelf zone is considered. The usefulness of the data available in regional information centres is discussed. The possibility of monitoring the dynamics of the oceanic fields in the tropical Atlantic encompassing separate observation sites is demonstrated using the oceanographic databank of the scientific research centre (CERESCOR) in Conakry-Rogbane as an example. The results of assimilation of the hydrophysical survey data derived on the shelf in a telescopic model of the region are given.Translated by Mikhail M. Trufanov.     

Numerical modelling of the seasonal variability of the North and Tropical Atlantic currents using an adaptation approach

The paper reports computed data on the seasonal variability of the Atlantic Ocean currents which were obtained through numerical integration (using conservative difference schemes) of non-linear equations of hydrothermodynamics taking into account an upper quasi-homogeneous layer and the bottom topography. The seasonal variability of the meridional heat transfer is discussed. The results were obtained using an adaptation approach.Translated by Vladimir A. Puchkin.     

Proper movement of a current meter mounted on a suspended drift station

In situ observations of the movement of a current meter attached to a long cable system of a drifting research vessel are discussed. A method is suggested which allows the cable configuration to be restored using measurement data on tangent orientation with respect to the given points. The compiled data indicate that the elements of the cable system shift by dozens of metres with a speed of the order of tens of cm per second. These shifts account for about 90% of the estimated value of current velocity energy pulsations in the frequency band corresponding to the proper frequency oscillations of the current meter and of the vessel's roll and-and-pitch motions.Translated by V. Puchkin.     

An application of a Markov-chain model of shore erosion for describing the dynamics of sediment flux

Acquisition of coastline retreat rate time sequences (RRTS) is an important component of Arctic coastal monitoring. These data can be used not only to estimate sediment input into the sea during a fixed time period, but also to dynamically simulate sediment flux intensity. The RRTS were investigated at the Marre-Sale (Kara Sea) and Malii Chukochii Cape (East Siberian Sea) key sites. Statistical analysis demonstrated that the RRTS possess Markov characteristic. This allowed coastline dynamics to be described using a Markov-chain model. A model is discussed that combines Markov characteristic and information about the composition and structure of the permafrost sediments to describe sediment flux dynamics.     

The Bengal Fan: Some preliminary results from ODP drilling

Three deep holes, with a maximum penetration of 960 m below sea floor, were drilled into the distal Bengal Fan just south of the equator during ODP Leg 116. The entire section recovered is dominated by sandy silt and mud turbidites derived from the Ganges Delta and from the continental margin of the western Bay of Bengal, interbedded with thin pelagic clays and with biogenic turbidites probably from a local sea mount source. The effects of Hi-Malayan uplift, sea level fluctuations, local tectonics, and fan channel/lobe processes have closely interacted to produce the observed sedimentary record of the past 17 million years since the early Miocene.Coauthors include: James R. Cochran, Lamont-Doherty Geological Observatory (Co-chief scientist); Dorrik A. V. Stow, Nottingham University, England (Co-chief scientist); Christian A. Auroux, Texas A & M University, USA (ODP staff scientist); Kazou Amano, Ibaraki University, Japan; Peter S. Balson, British Geological Survey, Keyworth, Notts, England; Jacques Boulegue, Pierre & Marie Curie University, Paris, France; Garrett W. Brass, University of Miami, Florida, USA; Jeffrey Corrigan, University of Texas, Austin, USA; Stefan Gartner, Texas A & M University, USA; Stuart A. Hall, University of Houston, Texas, USA; Silvia Iaccarino, University of Parma, Italy; Toshio Ishizuka, University of Tokyo, Japan; trena Kacmarska, Mount Allison University, New Brunswick, Canada; Heidemarie Kassens, Kiel University, West Germany; Gregory Leger, Dalhousie University, Halifax, Nova Scotia, Canada; Franca Proto Decima, University of Padova, Italy; C. V. Raman, Andhra University, Visakhapatnam, India; William W. Sager, Texas A & M University, USA; Kozo Takahashi, Woods Hole Oceanographic Institution, USA; Thomas Thompson, 580 Euclid Ave, Boulder, Colo, USA; Jean-Jacques Tiercelin, University of Bretagne, Brest, France; Mark Townsend, University of Nottingham, England; Andreas Wetzel, Tubingen University, West Germany; N. P. Wijayananda, National Aquatatic Resource Agency, Colombo, Sri Lanka; and Colin Williams, Lamont-Doherty Geological Observatory.     

Extension of the Narmada — Son lineament on the continental margin off Saurashtra,Western India as obtained from magnetic measurements

Magnetic total intensity values and bathymetric data collected on the continental margin off Saurashtra were, used to prepare magnetic anomalies and bathymetric contour maps. The magnetic anomalies are considered to have been caused by the Deccan Trap flood basalts which underlie the Tertiary sediments. Interpretation of the magnetic data using two-dimensional modelling method suggests that the magnetic basement is block faulted and deepens in steps from less than 1.0 km in the north to about 8.0 km towards the southern portion of the study area. The WNW-ESE trending faults identified in the present study extend across the Saurashtra continental margin between Porbandar and Veraval and appear to represent a major linear tectonic feature. The relationship of these fault lineaments with the regional tectonic framework have been discussed to indicate that they conform better as the northern boundary faults of the Narmada rift graben on the continental margin off Saurashtra.     

Validation of a finite difference method for the simulation of vortex-induced vibrations on a circular cylinder

The Karman Vortex Street generated by a circular cylinder is investigated by the numerical solution of the compressible Navier–Stokes equations in the incompressible Mach number range (Mach<0.3) using the Beam and Warming implicit scheme. The agreement with the fully incompressible projection method (Chorin, 1968) is fairly good while convergence time is very much better. The investigation suggests that the compressible Navier–Stokes equations may be used as an efficient alternative to study incompressible flows as well. Mach numbers just below 0.3 are enough to simulate incompressible flow behavior and at the same time do not cause numerical ill-conditioning in the solution. In addition, some relevant features of the vortices generated and carried by the wake of the cylinder could be fairly well captured.     

Directional spread parameter at intermediate water depth

The characteristics of directional spread parameters at intermediate water depth are investigated based on a cosine power ‘2s' directional spreading model. This is based on wave measurements carried out using a Datawell directional waverider buoy in 23 m water depth. An empirical equation for the frequency dependent directional spreading parameter is presented. Directional spreading function estimated based on the Maximum Entropy Method is compared with those obtained using a cosine power ‘2s' parameter model. A set of empirical equations relating the directional spreading parameter corresponding to the peak of wave spectrum to other wave parameters like significant wave height and period are obtained. It shows that the wave directional spreading at peak wave frequency can be related to the non-linearity parameter, which allows estimation of directional spreading without reference to wind information.