[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

Quantitative assessment of water levels and river discharge is often made difficult by large distances, limited access, and low population densities in remote areas. Satellite altimetry provides a repetitive remote sensing approach to determining river levels at a number of locations within a river system, providing the orbital repeat cycle is short enough in time, the ground track maintains a stable repeat over previous locations, and the return power of the altimeter signal can be readily identified and located. The U.S. Navy's Geosat radar altimeter mission between 1985 and 1989 provided the first altimeter measurements with sufficient precision and extended duration to examine the utility of such measurements for long‐term monitoring of inland waters. These measurements have been examined over the Amazon basin. Satellite observations are retrieved at four locations that overlap with river gauge measurements. A technique is developed to isolate radar return signals from the river. Two years of satellite measurements are compared with the river gauge retrievals. The overall level of comparison is 0.7 m rms when the technique is applied manually, and 1.2 m rms when an automated version of the method is applied. At one location the average difference is 0.2 m rms. This level of accuracy may not be useful for routine hydrological measurements. However, there are a variety of difficulties that are specific to the Geosat altimeter measurement over rough terrain. Present altimeter satellites, ERS 1 (launched June 1991) and TOPEX/Poseidon (launched August 1992), correct many of these problems. This study suggests that the prospect for obtaining useful measurements of river level from space is promising.

No abstract

--From January 9 to 17, 1981, detailed observations of the horizontal and vertical structure beneath one of the quasi-permanent semi-stationary mesoscale offshore eddy signatures in the California Current System (CCS) discussed by Bernstein, Breaker and Whritner (1977), Burkov andPavlova (1980), andSimpson (1982) were made. The vertical sections of temperature and density show the presence of a three-layer system. A subsurface warm-core eddy, whose diameter is about 150 km at the 7°C isotherm, is the dominant feature. A warm surface layer, which extends to a depth of 75 m, lies over the eddy. Between the warm surface layer and the subsurface warm-core eddy, there is a cold-core region which extends to a depth of about 200 m. There is a high degree of symmetry about the vertical axis of rotation. Vertical sections of salinity and dissolved oxygen are entirely different from sections of temperature and density. Diagrams of water mass characteristics confirm that the core of the eddy, found between 250-600 m, consists of inshore water from the California Undercurrent (CU). Below about 700 m, local waters from the Deep Poleward Flow (DPF) have been incorporated into the eddy. The observed distributions of properties (T, S, o-0, 02) are inconsistent with a single, local generation process for the eddy system. Radial distributions of angular velocity, normalized gradient velocity and relative vorticity support the use of a Gaussian radial height field as an initial condition in eddy models. Possible reasons why CCS eddies may differ dynamically from Gulf Stream rings are given in the text. At the time the observations were made, the system as a whole was in near geostrophic balance. Local geostrophic balance, however, cannot explain the observed distribution of properties and structure. The observed symmetry in the structure of the eddy system, chemical evidence (Simpson, 1984), biological distributions (Haury, 1984) and satellite images of the CC (Koblinsky, Simpson and Dickey, 1984) suggest that lateral entrainment of warm (oceanic) and cold (coastal) water into the upper two layers of the three-layer system by the subsurface eddy is a likely generation mechanism for the cold-core region. The coastal origin of the frontal structure along the northeastern quadrant and the oceanic origin of the frontal structure along the southwestern quadrant of the eddy system further support lateral entrainment as a generation mechanism for the cold core. This entrainment makes the CCS eddy system different from cold-core rings in the Gulf Stream and rather similar to some warm-core eddies found in the East Australian Current. The presence of CU water in the core of this eddy raises the question of how CU water was transported from the continental slope. Eddy generation mechanisms, other than baroclinic instability of the CC, may be required to explain the distribution, persistence, and core composition of offshore mesoscale eddies in the CCS. There is evidence that barotropic, in addition to baroclinic, processes may be i...