Guidelines and pitfalls of refraction microtremor surveys

Journal of Seismology - The geotechnical industry has widely adopted the refraction microtremor shear-wave velocity measurement technique, which is accepted by building authorities for evaluation...     

Electricity of the convective atmospheric boundary layer: Field observations and numerical simulation

The electric state of the middle-latitude convective atmospheric boundary layer (ABL) is investigated during a point in time when it is not disturbed by clouds, precipitation, mist, or industrial aerosols. A numerical model is developed that estimates the electroaerodynamic state of the convective ABL. The model is parameterized using results of field observations and laboratory experiments. According to the model, vertical profiles of atmospheric electric field strength, space charge density, electric conductivity, and atmospheric electric current density are calculated in the horizontally homogeneous approximation with a high space-time resolution.     

Reflection of long internal waves of small amplitudes from an underwater slope

The dynamics of long waves in the vicinity of a transition point of a two-layer flow into a single-layer one is studied within the linear theory of shallow water. The analogy between this problem and the classical problem of surface wave runup on the shore is shown. Conditions for breaking internal waves on a slope are discussed.     

Hydrophysical state of the Large Aral Sea in the autumn of 2013: Thermal structure,currents, and internal waves

This paper is focused on the hydrophysical state of the western basin of the Large Aral Sea in its present conditions of ecological crisis. The investigation is based on the direct observations carried out during a field survey in the Aral Sea in October of 2013. The analysis of the distribution of the temperature values across the western basin is given. Time series of the water currents variability were recorded at four mooring stations. The pattern of the basin-scale circulation response to the wind forcing was described. Based on the in situ measurements of the time variability of the temperature fields, the principal characteristics of the internal waves were specified for the present-day Aral Sea for the first time.     

Grain size trend and hydrodynamic condition of tirumalairajan River estuary,east coast of India

The estuary can be considered as environments characterized by high productivity and uncommensurable ecological value. However, marine ecosystems are also subjected to high human pressures that increase their vulnerability. The aim of this work is to analyze grain size trend of sediment due to the action of the main hydrodynamic condition. The spatial distribution patterns of sediments were monitored according to season. The grain-size trend of surficial sediments revealed a dominant sediment transport trend towards the eastern and south eastern part of study area. This study shows that there is an agreement among sediments path ways, hydrodynamic condition and the sediment spatial distribution in the estuarine environment. The agitation by waves is an important sorting mechanism in the study area. The findings are based on the grain size trend and also corroborated by short term observations of the estuarine sediment dynamics and transport during the monsoon, postmonsoon, summer and premonson seasons in Tirumalairajan River estuary.     

Structure of intrusions and fronts in the deep layer of the Eurasian basin and Makarov basin (Arctic)

Numerous CTD data obtained in the Eurasian and Makarov basins in the Arctic during the Polarstern (1996), Oden, and Louis S. St. Laurent (1994) international polar expeditions are analysed to describe fronts and intrusions observed in the deep layer (600–1300 m). The hydrological parameters were estimated from available CTD data, which made it possible to identify different types of fronts (baroclinic, thermohaline, and compound types of fronts) and analyze intrusive layering taking into account the peculiarities of the thermohaline structure of fronts. The field data are interpreted using an interleaving model describing the formation of intrusions on the baroclinic and pure thermohaline fronts under conditions of absolutely stable stratification. It is assumed that differential mixing is the main instability mechanism. Estimates of the vertical and lateral diffusivities in the frontal zones of the deep Arctic layer are presented.     

Possibilities of the photoluminescence method for determining the oxygen concentration in the redox zone of the Black Sea in comparison with other methods

Different methods of measuring low oxygen concentrations were compared in July 2008 in the Black Sea: the conventional Winkler method, electrochemical sensors (membrane and membrane-free), and two modifications of photoluminescence sensors. The membrane-free sensor used in the Black Sea since 1999 and the domestic photoluminescence sensor showed the best results: agreement of data, possibility of fine oxygen distribution resolution, and absence of the oxygen and hydrogen sulfide coexistence layer. The latter has good technical characteristics: high oxygen sensitivity and complete inertness to hydrogen sulfide, possibility of calibration in a gaseous environment, and a relatively low time constant (5–6 s). An equation was suggested for dynamic correction of data in the testing mode, which eliminates hysteresis of data on probe descent and ascent to a significant degree. It was shown that the oxygen concentration above the hydrogen sulfide layer in the subreductive zone of the Black Sea did not exceed 0.02 μM.     

Crucial physical characteristics of sea ice in the Arctic section of 143°–180°W during August and early September 2008

Sea-ice physical characteristics were investigated in the Arctic section of 143°-180°W during August and early September 2008. Ship-based observations show that both the sea-ice thickness and concentration recorded during southward navigation from 30 August to 6 September were remarkably less than those recorded during northward navigation from 3 to 30 August, especially at low latitudes. Accordingly, the marginal ice zone moved from about 74.0°N to about 79.5°N from mid-August to early September. Melt-pond coverage increased with increasing latitude, peaking at 84.4°N, where about 27% of ice was covered by melt ponds. Above this latitude, melt-pond coverage decreased evidently as the ice at high latitudes experienced a relatively short melt season and commenced its growth stage by the end of August. Regional mean ice thickness increased from 0.8 (±0.5) m at 75.0°N to 1.5 (±0.4) m at 85.0°N along the northward navigation while it decreased rapidly to 0.6 (±0.3) m at 78.0°N along the southward navigation. Because of relatively low ice concentration and thin ice in the investigated Arctic sector, both the short-term ice stations and ice camp could only be set up over multiyear sea ice. Observations of ice properties based on ice cores collected at the short-term ice stations and the ice camp show that all investigated floes were essentially isothermal with high temperature and porosity, and low density and salinity. Most ices had salinity below 2 and mean density of 800-860 kg/m~3 . Significant ice loss in the investigated Arctic sector during the last 15 a can be identified by comparison with the previous observations.     

Transformation of a strongly nonlinear wave in a shallow-water basin

The transformation of a nonlinear wave in shallow water is investigated analytically and numerically within the framework of long-wave theory. It is shown that the nonlinearity parameter (the Mach number), which is defined as the ratio of the particle velocity in the wave to the propagation velocity, can be well above unity in a deep trough and that a jump appears initially in the trough. It is demonstrated that shockwave amplitudes at large times change in accordance with the prediction of weakly nonlinear theory. The shock front generates a reflected wave, which, in turn, transforms into a shock wave if the initial amplitude is large enough. The amplitude of the reflected wave is proportional to the cube of the initial amplitude (as predicted by weakly nonlinear theory) over a wide range of amplitudes except for the case of anomalously strong nonlinearity. When there is a sign-variable sufficiently intense initial perturbation, the basic wave transforms into a positive shock pulse (crest) and the reflected wave turns into a negative pulse (trough).