Seasonal Variability Of Currents Research Articles

Variability of the Wind Stress, the Field of Currents, Wind Stress Curl and Vorticity of Surface Currents in the North Atlantic

The role of the Atlantic Ocean in climate changes in the Atlantic-European region determines the importance of studying spatial-temporal variability of the field of currents and the wind field generating the circulation of water in the ocean. The analysis of literature shows that data on seasonal variability of currents in the North Atlantic are controversial and reliable information on the interannual variability of ocean circulation in some regions of the North Atlantic it is impossible to obtain due to the lack of long oceanographic observations. The purpose of this study was clarifying seasonal changes and analyzing of interannual changes of the response of circulation of the upper layer of the North Atlantic on atmospheric forcing (wind stress and wind stress curl) by homogeneous and long-term datasets of re-analysis. Features of seasonal variability of wind stress, velocities of currents and their vorticity in subtropical and subpolar areas of the North Atlantic are confirmed. To the north of 15-20° of north latitude, seasonal variability of wind stress, velocities of currents and their vorticity generally accounts for less than one third of their total variability, the remaining dispersion is due to interannual and decennial fluctuations. In the Subtropical Atlantic in January there was a trend toward increased seasonal variability of wind stress, velocities of currents and anticyclonic wind stress curl and vorticity of surface currents in the second half of the 20th century. In September, since the mid-1970s, there is the tendency towards the weakening of these values, which leads to a long-term increase in the amplitude of the annual cycle. In the Subpolar Atlantic since the late 1950s, during the months with extreme values in the annual cycle there is an increase in seasonal variability of wind stress, velocities of currents and cyclonic wind stress curl and vorticity of surface currents. While, a significant increase in the amplitude of the annual cycle it is not revealed.

Seasonal variability of climatic currents in the Caspian Sea reconstructed by assimilation of climatic temperature and salinity into the model of water circulation

We present the results of an analysis of the seasonal variability of current fields in the Caspian Sea, reconstructed by assimilation of climatic temperature and salinity into the primitive-equation model of water circulation on the basis of an algorithm for adaptive statistics of prediction errors. The sources in heat and salt transfer-diffusion equations depend on the spatial and temporal variability of the variances of prediction errors and one-dimensional (in the vertical coordinate) variances of measurement errors for temperature and salinity. The variances of prediction errors are adjusted at the moments of data assimilation in accordance with a simplified Kalman filter. The climatic circulation of waters in the Caspian Sea is shown to be highly varying. The maximum of its intensity over the entire depth is reached in February. The minimum of kinetic energy is observed in April. The currents in deep-sea areas are determined by the balance between wind and baroclinic factors of the formation of circulation with wind currents prevalent.

Seasonal current variability on the New Jersey inner shelf

The well‐sampled ocean off the coast of New Jersey provides a data‐rich environment in which to study ocean current variability over the inner shelf. Using a year‐long HF radar data set, complemented with in situ and meteorological observations, the annual‐ and seasonal‐scale variabilities are examined. The hydrographic variability of the inner shelf off New Jersey is largely bimodal between summer stratification and winter mixing. An annual oceanographic and atmospheric data set was separated into these two regimes. The influence of stratification is evident through a relatively steady current response strongly correlated with the wind during the stratified season and a more variable response less correlated with the wind during the mixed season. When the water column is mixed, the influence of the local topography on the surface current variability is dependent on the slope, with a tendency for the variability to be more aligned with steeper topography.

Barotropic background currents in the Gulf of California

A field of barotropic background currents (BC) in the Gulf of California is constructed numerically. The definition of BC used here is based on suppositions about (i) the horizontal homogenization of potential vorticity in large-scale gyres, and (ii) the tendency of a current structure to evolve to a state with a minimum of system mechanical energy. In the barotropic case here, the numerical algorithm is reduced to the solution of the Dirichlet boundary problems for planetary, topographic and flowing integral streamfunction components separately. The results obtained are compared to observations and the results of other numerical models. The calculated barotropic BC realistically describe the main features of the circulation in the southern part of the Gulf of California, including its mouth. Cyclonic movement in the deep-water and anticyclonic movement near the coasts are observed. The numerical results for the central and northern parts of the gulf, where seasonal climatological differences are pronounced, coincide with observations in the upper layer only during the winter season; i.e., the circulation here is anticyclonic. Thus, there are reasons to suggest that mainly planetary-topographic forcing, especially in the southern part, forms the circulation in the lower layer. The seasonal variability of currents in the upper layer caused by non-stationary effects such as wind, heat flux and baroclinicity, is apparently in phase with these mechanisms during winter, and in antiphase during summer, particularly for the central and northern gulf.

Study of seasonal current variability in the Arabian Sea using Geosat altimeter data

The study of ocean circulation is required in climatic research, weather forecasting, navigation etc. Studying this phenomenon over larger spatial and temporal scales by conventional methods is very difficult. The advent of satellite altimetry gave ample opportunity to study ocean circulation repeatedly over larger areas. In this study Geosat altimeter derived sea level observations have been used to obtain monsoon departure current vectors over the Arabian Sea using geostrophic approximation. Current variability on the annual and seasonal bases is also studied. The circulation features are of the expected order. However, the departure current speeds near the Somali region are underestimated due to the limitation of the data. High current variabilities are present at places where large variations in current magnitude prevail.