[1] Particulate scattering and backscattering are two quantities that have traditionally been used to quantify in situ particulate concentration. The ratio of the backscattering by particles to total scattering by particles (the particulate backscattering ratio) is weakly dependent on concentration and therefore provides us with information on the characteristics of the particulate material, such as the index of refraction. The index of refraction is an indicator of the bulk particulate composition, as inorganic minerals have high indices of refraction relative to oceanic organic particles such as phytoplankton and detrital material that typically have a high water content. We use measurements collected near the Rutgers University Long-term Ecosystem Observatory in 15 m of water in the Mid-Atlantic Bight to examine application of the backscattering ratio. Using four different instruments, the HOBILabs Hydroscat-6, the WETLabs ac-9 and EcoVSF, and a prototype VSF meter, three estimates of the ratio of the particulate backscattering ratio were obtained and found to compare well. This is remarkable because these are new instruments with large differences in design and calibration. The backscattering ratio is used to map different types of particles in the nearshore region, suggesting that it may act as a tracer of water movement. We find a significant relationship between the backscattering ratio and the ratio of chlorophyll to beam attenuation. This implies that these more traditional measurements may be used to identify when phytoplankton or inorganic particles dominate. In addition, it provides an independent confirmation of the link between the backscattering ratio and the bulk composition of particles. Lee, M. Twardowski, E. Shybanov, G. Korotaev, and F. Baratange (2004), Particulate backscattering ratio at LEO 15 and its use to study particle composition and distribution,

[1] TOPEX/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-yearlong observations offer a new capability for interpretation of major transient and quasipermanent 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.

IntroductionRecent years have seen the broad application of remote sensing from space to oceanography. Altimetric missions that are designed for observations of surface geostrophic currents through the determination of dynamical topography of the sea surface (dynamical sea level) are of special importance. However, a wide variety of corrections needs to be applied to the raw altimeter measurements before retrieving the dynamical sea level. These corrections have a precision of a few centimeters, permitting the determination of dynamical sea level and surface geostrophic currents in the open ocean with reasonable accuracy. However, the geoid height, which must be subtracted from the altimeter sea surface, is only known to an accuracy of 10 cm at scales >1000 kin. At shorter scales this uncertainty is even worse. Therefore either temporal variability of geostrophic currents or their large-scale component is usually considered.There

[1] A field experiment was carried out in summer 2002 on an oceanographic platform near the coast of Crimea, in the Black Sea. For the first time, the spectral volume scattering function (VSF) was measured for a wide range of scattering angles (i.e., from 0.6 to 177.3 degrees) using a recently developed device. Our analysis revealed that the mineral particles are the primary component influencing the scattering and backscattering coefficient in the study area. The good correlation obtained between the backscattering coefficient b bp and the nonalgal particles absorption coefficient showed that the absorption efficiency of the mineral particles is high in the second half of the experiment. The ratio Chla/c p (where Chla is the chlorophyll a concentration and c p is the beam attenuation coefficient) did not correlate with the backscattering ratio and thus could not be used in this experiment as an alternative proxy to estimate the bulk composition of the particles. The spectral variation of b p (the scattering coefficient) and b bp (the backscattering coefficient) was less steep than what can be found in the open ocean waters. That was explained by the influence of the absorption on the scattering process, especially in the blue, as a consequence of the anomalous dispersion. The average backscattering ratiõ b bp varied spectrally within 4%. Nevertheless, a high spectral variability ofb bp (around 30%) was observed suggesting that the use of a flat spectral variation is not accurate in coastal zones.

The volume scattering function (VSF) of natural bubble populations is (1) determined from Mie scattering theory, (2) measured by a newly designed volume scattering meter in the laboratory, and (3) inferred from field observations of the VSF. The laboratory measurements have confirmed our theoretical prediction in that (1) bubbles of sizes that have been recorded in situ in the surface ocean (Ͼ10 m) show elevated scattering for angles between 60Њ and 80Њ and (2) the organic coatings on the bubble surface will increase the scattering in the backward hemisphere but little change the scattering in the forward directions, including the critical angles. An optimization analysis is applied to the measurement of the VSF in coastal waters, and the results suggest the potential existence of submicron bubbles that are coated with organic film. The bubble population thus determined, which has a negligible contribution to the total scattering (5%), accounts for 40% of the total backscattering that has been observed in situ. The extension of the bubble size distribution to smaller sizes than can presently be measured by direct techniques will alter the shape of derived phase function in general but will result in rather small changes to the backscattering ratio (Ͻ20%) as long as the slope of the size distribution is small, because most of the changes are in the forward (Ͻ10Њ) direction. However, the prominent peak in the VSF at the critical angle observed for larger bubbles is strongly reduced by the inclusion of the small sizes, and the backscattering ratio is increased by a factor of two for distributions that varies as the Ϫ4 power of size. Because these bubbles contribute strongly to scattering at large angles, these results have significant implications for the remote observation of the color of the sea.Remote observations of the spectral distribution of light backscattered from the upper ocean provide the only practical means for diagnosing the spatial and temporal varia-

Abstract. The paper presents the development of the Black Sea community nowcasting and forecasting system under the Black Sea GOOS initiative and the EU framework projects ARENA, ASCABOS and ECOOP. One of the objectives of the Black Sea Global Ocean Observing System project is a promotion of the nowcasting and forecasting system of the Black Sea, in order to implement the operational oceanography in the Black Sea region. The first phase in the realization of this goal was the development of the pilot nowcasting and forecasting system of the Black Sea circulation in the framework of project ARENA funded by the EU. The ARENA project included the implementation of advanced modeling and data assimilation tools for near real time prediction. Further progress in development of the Black Sea nowcasting and forecasting system was made in the frame of ASCABOS project, which was targeted at strengthening the communication system, ensuring flexible and operative infrastructure for data and information exchange between the Black Sea partners and end-users. The improvement of the system was made in the framework of the ECOOP project. As a result it was transformed into a real-time mode operational nowcasting and forecasting system. The paper provides the general description of the main parts of the system: circulation and ecosystem models, data assimilation approaches, the system architecture as well as their qualitative and quantitative calibrations.

The dynamics of a Gaussian isolated barotropic eddy on a β-plane is considered. The analytical solution of the evolution of an isolated vortex is constructed by analogy to the theory of a point vortex. The results of a numerical experiment are compared with the conclusions of the theory for the case of the Gaussian vortex. Characteristics of the vortex such as its radius, trajectory of movement, kinetic energy, residual vorticity, and the structure of the vortex are discussed. The analysis of the numerical results shows that the experimentally determined radius of the vortex, its energy, and residual vorticity are in good agreement with the theory. On the other hand there is a difference between analytical and experimental values of velocity components, and hence in the trajectory of the centre of the vortex. The location of the separatrix of the streak function and its saddle point are considered as important characteristics of the structure of the vortex. We consider the phenomenon of the generation of the vortex sheet connected with the separatrix location as a cause of the difference between the experimental and analytical estimates of the velocity of the vortex.

[1] The particulate backscattering coefficient b bp is an inherent optical property that plays a central role in studies of ocean color remote sensing. Because of practical difficulties associated with measurements of the volume scattering function (VSF) over the whole backward hemisphere, b bp is currently derived using fixed-angle backscattering sensors and applying a conversion factor for particulate backscattering, referred to as c p . The underlying assumptions of the fixed-angle approach are as follows: (1) in the green band, c p is fairly constant in the angular range 100°-150°and (2) for a fixed scattering angle, c p is wavelength-independent. In this study we investigated the variability of c p based on spectral measurements of the full VSF, both in situ and for algal culture in the laboratory. The in situ data used in our study were acquired in a coastal environment outside of phytoplankton blooms, whereas the laboratory data were representative for phytoplankton bloom conditions in oceanic waters. At 555 nm, c p was found to vary significantly in the angular range 100°-130°, and at 140°, c p was found to be weakly variable in nonblooming waters only. The spectral variability of c p was studied for the first time, and the spectral slopes of c p , measured in situ, were found to vary within ±6%. Under the assumption that c p (140°) is wavelength-independent, the induced error in the estimates of b bp was found to be lower than 10%. The algal culture showed a much higher spectral variability in c p (±20%), which induced an error in the estimates of b bp up to ±25.8%.Citation: Chami, M., E. Marken, J. J. Stamnes, G. Khomenko, and G. Korotaev (2006), Variability of the relationship between the particulate backscattering coefficient and the volume scattering function measured at fixed angles,