Alexander G. Ostrovskii

Direct Measurements of Deep Currents in the Northern Japan Sea

Long-term current measurements by means of subsurface moorings were made for the first time at seven sites in the Japan Basin, the northern part of the Japan Sea. The objective was to directly explore the velocity field in the highly homogeneous deep water mass (the Japan Sea Proper Water) that occupies depths below 500 m. On each mooring three current meters were equipped at an approximately equal distance below about 1000 m depth. Duration of the measurements was 1 to 3 years depending on specific site. This paper describes the basic data set from the moored measurements. It is found that the deep water of the Japan Basin is very energetic with eddies and vertically coherent currents of the order of 0.1 m/s. Surprisingly, the currents and eddies exhibit strong seasonal dependence even in the deepest layers of the Basin. The observed new current features are discussed in comparison with conventional deep circulation pictures derived from hydrographic data.

Submesoscale Eddies at the Caucasus Black Sea Shelf and the Mechanisms of Their Generation

The results of observations of submesoscale eddies (with a diameter of 2–8 km) on the narrow Black Sea shelf are presented. These observations were carried out in the Gelendzhik region in the autumn seasons of 2007–2008 using traditional and new methods of hydrophysical investigations. The mechanisms of generation of such eddies are discussed.

Quasi‐biennial variability in the Japan Sea

The TOPEX/Poseidon (T/P) altimetry reveals quasi-biennial (QB) variability in the southern Japan Sea. Sea surface height anomalies of a biennial nature are most energetic in the Yamato Basin, the southeastern most part of the Japan Sea, where they can be as large as 20 cm and extend for 100–200 km. On the basis of the in situ measurements of Maizuru Marine Observatory, the 2–3 year variations are associated with thermohaline anomalies in the upper 300 m layer. The local QB oscillation is studied with a reduced gravity model of the Japan Sea. The model is forced by European Centre for Medium-Range Weather Forecasting daily wind and seasonal inflows/outflows through the three major straits of the sea. The model sensitivity experiments suggest that the QB variability can be associated with the seas response to wind forcing of particular years, more specifically, 1992 and 1996, and to some extent, 1994. An approximate Kaiman filter is employed for assimilation of the T/P altimeter data into the reduced gravity model. It filters out observational noise and intraseasonal sea level variability and allows the model to dynamically interpolate T/P observations. The results of the assimilation indicate that the QB anomalies are strongest at 37.5°N, 134.5°E and propagate west-northwest with a speed of ∼0.01 m s-1, contributing to variations of the Tsushima Warm Current.

Inversion for heat anomaly transport from sea surface temperature time series in the northwest Pacific

We describe a heat anomaly transport in the upper ocean mixed layer in the Kuroshio extension region and the subtropical gyre of the northwest Pacific. Emphasis is on behavior in the cool season December-March) during the Asian Winter Monsoon. The heat anomaly transport is estimated by applying an inversion technique to the stochastic partial differential equation for the heat anomaly balance of advection, diffusion, subilizing feedback, and atmospheric forcing. The inversion consists of (1) derivation of statistical parametric model from the heat anomaly balance equation; (2) fitting the derived statistical model to the sea surface temperature (SST) anomaly covariances; and (3) calculation of the heat anomaly net advection velocity, horizontal diffusion coefficient, feedback factor and atmospheric forcing correlation from the parameters of the evaluated statistical model. The inversion was applied to the Comprehensive Ocean-Atmosphere Data Set Compressed Marine Reports SST data averaged at 1 o latitude ×2 o longitude boxes on a 10-day mean basis from 1965 to 1990. The estimates of the net advection velocity are consistent in magnitude and direction with the general circulation in the surface layer of the Northwest Pacific in winter. SST anomalies are transported to the west at ∼0.15 m s -1 in the northern part of the North Equatorial Current. Between 21 o and 29 o N in the recirculating region, SST anomalies propagate westward with the mean velocity less than 0.1 m s -1 . South and east of Honshu the observed pattern of the SST anomaly transport agrees broadly with the circulations of the Kuroshio current and its extension and the Oyashio current. South of Honshu, the eastward transport is about 200-300 km wide; its absolute velocity is up to 0.2 m s -1 . One branch of the uansport separates from the coast near the large meander path of the Kuroshio current and follows the east-southeast direction. The second separation from the coast occurs south of Hokkaido. Over the analysis domain the estimates of the diffusion coefficient are in the range of 3×10 3 to 6x10 3 m 2 s -1 . The h igher values of the diffusion coefficient confirm the enhancement of the mesoscale eddy processes near the subtropical convergence zone. The analysis supports Hasselmanns (1976) theory in which generation of midlatitude SST anomalies lasting the dominant timescale of atmospheric processes is primarily attributed to the short period stochastic weather forcing. However, the analysis indicates that the inertia of SST anomalies to ther memory of earlier winds can not be neglected in the vicinity of the western boundary and in the tropics

Subsatellite polygon for studying hydrophysical processes in the Black Sea shelf-slope zone

The first data on the creation of the subsatellite polygon on the Black Sea shelf and continental slope in the Gelendzhik area (designed in order to permanently monitor the state of the aquatic environment and biota) and the plans for maintaining and developing this polygon are presented. The autonomous measuring systems of the polygon in the composition of bottom stations with acoustic Doppler current profilers (ADCP), Aqualog robotic profilers, and thermo-chains on moored buoy stations should make it possible to regularly obtain hydrophysical, hydrochemical, and bio-optical data with a high spatial-time resolution and transmit these data to the coastal center on a real-time basis. These field data should be used to study the characteristics and formation mechanisms of the marine environment and biota variability, as well as the water-exchange processes in the shelf-deep basin system, ocean-atmosphere coupling, and many other processes. These data are used to calibrate the satellite measurements and verify the water circulation numerical simulation. It is assumed to use these data in order to warn about the hazardous natural phenomena and control the marine environment state and its variation under the action of anthropogenic and natural factors, including climatic trends. It is planned to use the polygon subsatellite monitoring methods and equipment in other coastal areas, including other Black Sea sectors, in order to create a unified system for monitoring the Black Sea shelf-slope zone.

Interdecadal variations of ENSO signals and annual cycles revealed by wavelet analysis

Interdecadal variations of El Niño/Southern Oscillation (ENSO) signals and annual cycles appearing in the sea surface temperature (SST) and zonal wind in the equatorial Pacific during 1950–1997 are studied by wavelet, empirical orthogonal function (EOF) and singular value decomposition (SVD) analyses. The typical timescale of ENSO is estimated to be about 40 months before the late 1970s and 48–52 months after that; the timescale increased by about 10 months. The spatial pattern of the ENSO signal appearing in SST also changed in the 1970s; before that, the area of strong signal spread over the extratropical regions, while it is confined near the equator after that. The center of the strongest signal shifted from the central and eastern equatorial Pacific to the South American coast at that time. These SST fluctuations near the equator are associated with fluctuations of zonal wiond, whose spatial pattern also shifted considerably eastward at that time. In the eastern equatorial Pacific, amplitudes of annual cycles of SST are weak in El Niño years and strong in La Niña years. This relation is not clear, however, in the 1980s and 1990s.

Multisensor satellite monitoring of seawater state and oil pollution in the northeastern coastal zone of the Black Sea

A new approach aimed at a better understanding of the state of pollution of the Black Sea coastal zone is suggested. It consists of the combined use of all available quasi‐concurrent satellite information (NOAA AVHRR, TOPEX/Poseidon, Jason‐1, Terra/Aqua MODIS, Envisat ASAR, ERS‐2 SAR and QuikSCAT) and was first applied during an operational seawater monitoring campaign in the coastal zone of the northeastern Black Sea conducted in 2006. The monitoring is based on daily receiving, processing and analysis of data different in nature (microwave radar images, optical and infrared data), resolution and surface coverage. These data allow us to retrieve information on seawater pollution, sea surface and air–sea boundary layer conditions, seawater temperature and suspended matter distributions, chlorophyll‐a concentration, mesoscale water dynamics, near‐surface wind, and surface wave fields. Such an approach helps in oil spill detection with synthetic aperture radar (SAR), especially in distinguishing oil slicks from look‐alikes. The focus is on coastal seawater circulation mechanisms and their impact on the evolution of pollutants.

Inversion of Upper Ocean Temperature Time Series for Entrainment, Advection, and Diffusivity

Abstract An inversion technique for estimating the terms of the oceanic near-surface heat transport is extended to include the vertical heat flux at the bottom of the surface mixed layer. The mixed-layer heat balance equation uses a conventional parameterization of the vertical heat flux via entrainment into the mixed layer of interior fluid during the mixed layer deepening. A heat conservation equation defined here for the sea temperature anomalies, deviations from the annual cycle, is driven by stochastic atmospheric forcing, thereby becoming essentially a stochastic partial differential equation. This equation is reduced to the regression estimator aimed on inversion of the sea temperature time series for the unknowns: vertical entrainment velocity, horizontal velocity and diffusivity, feedback factor, and atmospheric forcing parameter. The inversion scheme also involves the velocity divergence norm. The regression estimator is applied to the time series of vertical profiles of temperature anomalies co...

Signatures of stirring and mixing in the Japan sea surface temperature patterns in autumn 1993 and spring 1994

A wavelet analysis of the NOAA satellite radiometry data shows remarkable difference in the typical patterns of the sea surface temperature (SST) of the Japan Sea in autumn 1993 and spring 1994. The plumes of irregular shapes with characteristic horizontal scale of less than 30 km developed over the SST field at the beginning of the cooling season when the horizontal temperature gradients were essentially eroded. In contrast, very narrow and elongated up to 100 km streaks appeared at the beginning of the heating season when the temperature gradients were sharp. The spectral analysis of SST results in the power law behavior of k −2.0 in October and k −2.8 in May, for the scales ranging from 10 km to 100 km. This research suggests that the surface cooling in the autumn favors the enhancement of three dimensional mixing, while during the onset of heating the horizontal stirring becomes more pronounced at geostrophic turbulence scales.

Autonomous System for Vertical Profiling of the Marine Environment at a Moored Station

This paper presents new results of the research and development project on the moored profiler Aqualog aimed at multidisciplinary studies and ecological monitoring of the marine environment. The data on the profiler’s operation are summarized based upon the field experiments in the northeastern Black Sea in 2011. An important scientific result obtained by using the profiler during the experiments was the discovery of the countercurrent below the Black Sea Rim Current in the layer between the 500 m and 900 m depth.