K. D. Sabinin

“Hot spots” in the field of internal waves in the ocean

A review of observations of high-amplitude internal waves is presented. These waves play an important role in the global scenario of water mixing in the world ocean and also cause a considerable variability of oceanographic fields, including the sound velocity field. The main sources of intense internal waves and the regions where such waves arise are considered. It is shown that, in addition to the much-investigated trains of soliton-like internal waves, which are formed near large-scale inhomogeneities of the bottom relief because of the nonlinear evolution of internal tides, internal waves encountered in the open ocean also possess considerable amplitudes and nonlinearity.

Anisotropic field of background internal waves on a sea shelf and its effect on low-frequency sound propagation

The space-time spectral characteristics of the field of background internal waves (IW) are obtained for two oceanic shelf regions (the Atlantic shelf of the United States and the Kamchatka shelf) and analyzed. Within the framework of a numerical experiment, it is shown that the observed anisotropy of the IW field may considerably affect the low-frequency sound fluctuations in the aforementioned regions and, in particular, may change the interference invariant of the sound field.

Study of internal wave generation and propagation features in non-tidal seas based on satellite synthetic aperture radar data

Despite the intense attention paid to internal wave (IW) investigation, the most experimentally studied and theoretically described are internal gravitational waves in shelf zones of oceans and tidal seas appearing during the interaction of tidal currents with the margin of the shelf. Information on surface manifestations of internal waves in enclosed seas, such as the Black and Caspian seas, is almost absent. In this paper, the results of study of the peculiarities of generation and propagation of nontidal internal waves are presented; the study is carried out on the basis of combined analysis in data of marine surface radiolocation and data of optical and infrared satellite-borne sensors. The experimental basis of investigation is radar images of the marine surface derived with the help of Synthetic Aperture Radars, onboard the Envisat and ERS-2 satellites. Additionally, the data of the following sensors belonging to the optical and infrared ranges were used for the purpose of radar image interpretation: MODIS (onboard the Aqua/Terra satellite), MERIS (Envisat), and AVHRR (NOAA). Surface manifestations of IWs in the northeastern part of the Black Sea and in the Caspian Sea have been found in radar imagery for the first time, their pattern of spatial and temporal variation has been reconstructed. The possible factors leading to generation of the observed nontidal IWs are determined and suppositions about the corresponding generation mechanisms are made. In particular, the IW manifestations recorded in the northeastern part of the Black Sea are localized in the vicinity of the boundaries of eddies or hydrological fronts; this fact evidences for the frontal mechanism of generation, at which IWs are radiated by a nonstationary (moving and/or inertially oscillating) front. The most probable main sources of generation of IWs detected in the Caspian Sea are longitudinal one-knot seiches, whose knot point is located near the Apsheron sill.

Anomalous variation of the ocean’s inertial oscillations at the Hawaii shelf

The data of acoustic Doppler profilometers placed at the edge of the steep shelf of Oahu Island, Hawaii, are analyzed for the currents. The specific character of inertial oscillations is revealed in the region: strong elongation of inertial orbits, a large amount of anomalous (cyclonic) current rotation, and sharp weakening in the divergence layer of the background (low-frequency) oscillations, the strong variation of which results in significant deviations of the effective inertial frequency from its local geographical value. It is suggested that cyclonic rotation of the inertial currents is related to a strong decrease in the effective oscillation frequency of the oceanic waves on the shelf.

Satellite observations of surface manifestations of internal waves in the Caspian Sea

Results of satellite observations of surface manifestations of internal waves in the Caspian Sea are presented. It is proposed that the possible cause of generation of the revealed internal waves is uninodal seiches with a nodal line located in the vicinity of the Apsheron Sill. The basic parameters of internal waves in the Caspian Sea, having the form of classical soliton trains, are determined. Seasonal variability of surface manifestations of the internal waves is revealed. The horizontal current velocity of the solitons is assessed. According to the estimation, velocity is about 0.2 m/s, which is sufficient for wind ripple modulation.

Resonant and nonresonant mechanisms of forming space radar images of the ocean

Abstract The paper considers two approaches to quantitative description of the microwave backscatter from the ocean surface: resonant and nonresonant. It is shown that the theories based on the resonant (Bragg) approach do not explain all the observed phenomena at low grazing angles. A new, nonresonant mechanism of scattering, which involves scattering from steep, breaking waves, is suggested.

Characteristics of inertial oscillations according to the experimental measurements of currents on the Russian shelf of the Black Sea

The analysis of inertial oscillations on the Gelendzhik shelf of the Black Sea is presented. Spectral characteristics of the current fields are studied based on the measurements taken by the acoustic Doppler current profiler. Strong variability of the inertial oscillation hodographs at variations in the background shear current and diverse forms of inertial oscillations measured at a fixed point at various values of the shear current are revealed. The relation between the passage of the multidirectional jets and the trains of inertial oscillations inside the jets in the studied region are established.

Study of fields of currents and pollution of the coastal waters on the Gelendzhik shelf of the Black Sea with space data

AbstractsThis paper presents the results of hydrophysical measurements and processing of space imagery of the fields of currents and pollution of the coastal waters on the Gelendzhik shelf of the Black Sea. The results of measurements with a towed acoustic Doppler profiler reveal the strong spatial and temporal variability of the fields of near-surface currents and impact of the deep discharge on the dynamics of coastal waters. The characteristics of the near-surface seawater pollution are studied under the influence of the submerged outfall. The analysis of space imagery of high spatial resolution reveal small-scale optical seawater heterogeneities caused by intense anthropogenic impact directly on the Gelendzhik Bay, the surface influence of the submerged outfall on the coastal waters, and the pollution jet area.

Detection of convective instability in atmospheric boundary layer over the ocean by airborne Ku-band real aperture radar

The paper examines structural features of radar images obtained under unstable stratification of the ocean-atmosphere boundary layer. Manifestations of the dry and moist convective cells are of special interest. Near surface convective processes in radar images are investigated at different sounding directions relative to the mean surface wind. Images recorded by airborne side looking real aperture radar at a wavelength of 2.25 cm are considered. Radar images under discussion were recorded during joint Russia/US experiment JUSREX conducted in July 1992 in an area off the US coast, roughly 80 km south east of Long Island, New York.

Results of using acoustic doppler current profilers for studying the spatial structure of the marine environment

The possibilities of using towed and anchored acoustic Doppler current profilers for studying the fine spatial structure of sea waters are analyzed. Typical errors are discussed and new possibilities of using the current profiler data for studying small-scale eddies and internal waves, as well as the divergence in the current field, are considered. Examples of small-scale inhomogeneities encountered on sea shelves are presented.