Gennady K. Korotaev

Seasonal, interannual, and mesoscale variability of the Black Sea upper layer circulation derived from altimeter data

[1]xa0TOPEX/Poseidon and ERS altimeter data comprising the period from May 1992 to May 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the Black Sea. These 7-year-long observations offer a new capability for interpretation of major transient and quasi-permanent features of the upper layer circulation. The instantaneous flow fields involve a complex, eddy-dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders, and filaments of the Rim Current. The circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year-to-year variability. An organized two-gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months, which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system. Our analyses suggest a revised schematic circulation picture of the major quasi-permanent and recurrent elements of the Black Sea.

Validation of the NOAA/NESDIS satellite aerosol product over the North Atlantic in 1989

A validation experiment and resulting potential improvements to the operational satellite aerosol optical thickness product at the National Oceanic and Atmospheric Administration/National Environmental Satellite Data and Information Service (NOAA/NESDIS) are presented. An earlier paper described a set of Sun photometer measurements collected from the Soviet R/V Akademik Vernadsky during its cruise in the Atlantic Ocean and Mediterranean Sea from September to December 1989. The accuracy of the Sun photometer aerosol optical thickness was proven acceptable for use as a ground truth standard for validation of the NOAA product. This paper describes the validation methodology and the results of its application to the NOAA 11 satellite product. A systematic underestimation in the operational values by about 35%, relative to the ship truth, is found. Causes for this discrepancy are examined, emphasizing the importance of careful satellite instrument calibration, and a revision of the oceanic reflectance model used in the retrieval algorithm. It is shown that the remaining systematic underestimate in satellite aerosol optical thickness can be attributed only to the aerosol model used in the retrieval. Additional checks of this conclusion using independent data sets are underway. If confirmed, a fundamental revision of the presently used aerosol model would be required. An example of a simple adjustment to the present aerosol model which successfully removes the bias is given, based on the assumption of an absorbing aerosol.

Parameterization of light absorption by components of seawater in optically complex coastal waters of the Crimea Peninsula (Black Sea)

The absorption of sunlight by oceanic constituents significantly contributes to the spectral distribution of the water-leaving radiance. Here it is shown that current parameterizations of absorption coefficients do not apply to the optically complex waters of the Crimea Peninsula. Based on in situ measurements, parameterizations of phytoplankton, nonalgal, and total particulate absorption coefficients are proposed. Their performance is evaluated using a log-log regression combined with a low-pass filter and the nonlinear least-square method. Statistical significance of the estimated parameters is verified using the bootstrap method. The parameterizations are relevant for chlorophyll a concentrations ranging from 0.45 up to 2 mg/m(3).

Data Assimilation of Satellite Images Within an Oceanographic Circulation Model

We tackle the problem of coupling a geophysical simulation model with data coming from image processing. It needs to define the image observation space and to design an operator to transform results from the image space to the model space. In this study, we use a shallow-water oceanographic circulation model developed at MHI. We propose a processing chain first based on an image processing step relying on a dedicated motion estimation operator, and then a data assimilation step of the estimated velocity. We illustrate the method on different results without and with assimilation

International Subsatellite Experiment on the Oceanographic Platform (Katsiveli, Crimea)

We present the description and preliminary results of the international subsatellite experiment carried out on the oceanographic platform located in the Black Sea (near the South Coast of Crimea in the region of Katsiveli). A brief description of the equipment and experimental procedure is given. Some preliminary results of the experiment, including the data on the behavior of biooptical parameters as functions of time and their correlation, are presented. These data cover a broad range of variation of the biooptical properties of the sea and can be used for the quantitative comparison with the data of the MERIS, MODIS, and SeaWiFS scanners.

Estimation of a Motion Field on Satellite Images from a Simplified Ocean Circulation Model

This paper aims at estimating the apparent velocity from sequences of satellite images. This study is an illustration of a more general methodology for generating, from satellite images, pseudo-observations of physical variables, that are assimilated within a geophysical forecast model in view of improving the quality of its results. In the case of the presented study, the used satellite images are sequences of sea surface temperature (SST), from which pseudo-observations of sea surface velocities are generated, and assimilated within an ocean circulation model. The originality of the approach lies in the definition of an image model, that predicts the evolution of image information -here, SST- as a function of the pseudo-observations -here, surface velocity-. Satellite data are then assimilated within the image model, yielding an estimation of the pseudo-observations. In the case of this paper, this methods allows the estimation of sea surface velocities, even when large parts of the satellite images are corrupted by clouds. The image model plays the role of an intermediate model, between satellite data and the forecast model, and allows the assimilation of image information which is not directly linked to the state variables of the forecast model.

Consequences of Land and Marine Ecosystems Interaction for the Black Sea Coastal Zone

The Normalized Difference Vegetation Index (NDVI) was used for the analysis of ecological characteristics of the Northwest Black Sea region, which includes significant coastal territories and sea water areas between the Crimean and northwest coast of the Black Sea. The data used in this study were 1997–2008 monthly NDVI from NOAA’s GVI2 dataset and visible channels from 1998 to 2008 from MODIS (Aqua and Terra) and SeaWiF scanners. It is shown, that the NDVI can be used as the characteristic of the integrated “land–sea” ecosystem, including internal links in this system. There is a direct-proportional relationship between NDVI in the land coastal zone and near-coastal water optical–biological characteristics. Although the NDVI values for water are small compared to the atmospheric signals (aerosol and molecular scattering) the resulting estimations have shown, that the possible relative error of the NDVI measurement for the northwest area of the Black Sea is within 12–25%.