Staircase and inversion structures of thermocline in the north-west Tropical Atlantic

The peculiarities of the vertical fine thermohaline structure of waters in the north-west Tropical Atlantic are considered on the data of STD surveys recorded in winter-spring 1984. The variability of the characteristics of staircase and inversion elements of stratification with depth is analysed over the horizontal as well as related to the mesoscale and large-scale dynamics of waters. The coefficients of horizontal turbulent exchange are estimated within the framework of Joyce's hypothesis on quasi-compensation of vertical and turbulent horizontal transport. The effects of double diffusion are considered to dominate in vertical transport.UDK 551.465.15Translated by Mikhail M. Trufanov.     

Vertical exchange in the ocean

We analyze the expressions for vertical turbulent flows and the coefficients of turbulent exchange in the ocean and their dependences on the stratification of density. It is shown that, in the case of high density gradients, turbulent mixing is localized in separate bounded relatively small zones (turbulized spots or layers). Formulas for typical vertical sizes of turbulent spots and local coefficients of vertical turbulent exchange depending on the Väisälä-Brunt frequency are presented. We consider a model of vertical turbulent exchange for the case of spot-like intermittent turbulence (a similar model was independently developed at the Marine Hydrophysical Institute of the Ukrainian Academy of Sciences with certain differences in the statement the problem and methodology). We emphasize the priority of A. G. Kolesnikov in the investigations of vertical turbulent exchange in the ocean by the direct method, in the development and construction of quick-response measuring devices with detectors of pulsations of the components of velocity and temperature, and in the first determination of the characteristics of turbulence in lakes, seas, and oceans performed by using this equipment.     

Spatial spectra and characteristic horizontal scales of temperature and velocity fluctuations in the convective boundary layer of the atmosphere

Using a high-resolution LES numerical model, we calculated the turbulent thermal convection for high ratios of horizontal and vertical sizes of the computational domain (26: 26: 1). The natural analog of the simulated process is a planetary boundary layer (PBL) of the atmosphere growing with height in the background of stably stratified overlying air layers over a horizontally homogeneous heated surface under a weak average wind. We obtained the spectral distributions of variances of fluctuations in potential temperature and velocity components in ranges corresponding to scales from a few tens of meters to a few tens of kilometers. We found energetically significant segments of the spectrum of large-scale fluctuations in the potential temperature for which the power dependences S ～ k ^?1/3 and S ～ k ^?4/3 are satisfied with good accuracy. We calculated the characteristic spatial scales of horizontal fluctuations in velocity and temperature. We obtained a dependence of these scales on the height of the growing convective PBL. We discuss the characteristic features of large-scale distributions in terms of the self-similarity of the growing boundary layer behavior.     

Experimental determination of small-scale turbulence coefficients in the near-surface layer of the sea

The results of numerous experiments on the diffusion of fluorescent dyes are presented. To determine the turbulent diffusion coefficients, the technique involving under water photography of a jet with the subsequent processing of negatives by a microphotometer was used. The vertical coefficients were found to be slightly larger (by about 20%) than the horizontal ones, with the scale of the phenomenon being 0.3–1 m. Empiric relationships have been derived for the turbulent diffusion vertical coefficient on the parameters of surface waves.Translated by V. Puchkin.     

Dynamics of trace gases and aerosols in the atmosphere with consideration for heterogeneous processes

A combined mathematical model has been developed to reproduce space and time variations in the concentrations of multicomponent gas constituents and aerosols in the atmosphere on both regional and urban scales. This model contains blocks of transport of gas constituents and aerosols in the atmosphere with consideration for homogeneous binary nucleation, the kinetic processes of condensation/evaporation and coagulation, chemical processes occurring in both gas and liquid phases, and the processes of mass exchange during the gas-droplet (particle) interaction. A nonhydrostatic model of atmospheric mesoscale processes is used to calculate the fields of meteorological elements and turbulent characteristics. The generation of new-phase particles from precursor gases by the mechanism of homogeneous binary nucleation and their interaction with background aerosol are considered. The results of numerical experiments are compared with the data obtained from field observations of both space and time variations in the concentrations of gas constituents and aerosols and in the ionic content of aerosol particles over the Baikal region under the influence of emissions from powerful industrial sources.     

Evaluation of the influence of surface films on short wind waves and the characteristics of the boundary layer of the atmosphere

With the help of a combined model of wind and waves, we study the influence of films of surfactants on the spectrum of short wind waves and the parameters of the lowest layer of the atmosphere. It is shown that the films of surfactants decrease the roughness of the sea surface as a result of suppression of short wind waves, which decreases the coefficient of resistance of the sea surface and the coefficient of turbulent heat exchange. The maximum influence of films on the exchange coefficients is attained forU∼10 m/s. In this case, the relative decrements of the coefficients of resistance and turbulent heat exchange are equal to 15 and 9%, respectively. Translated by Peter V. Malyshev and Dmitry V. Malyshev UDC 551.46     

Evaluation of the coefficients of horizontal exchange in the Black Sea according to the data of drifter experiments

We generalize the method used for the evaluation of the coefficients of horizontal diffusion of Brownian particles to the nonstationary case, as applied to the drifter experiments. The limits of applicability of the proposed procedure are determined. The coefficients of horizontal exchange are computed with an aim to compare them with the estimates obtained earlier by using the generalized Taylor theory. The mutual agreement of these estimates is demonstrated. It is shown that the difference between the values of the zonal (0.19⋅10⁴ m²/sec) and meridional (0.11⋅10⁴ m²/sec) coefficients of exchange in the Black Sea cannot be explained by the effect of increase in the longitudinal component of pulsations of the velocity as a result of its transverse shear relative to the mean current. A conclusion is made that the processes of horizontal exchange in the Black Sea are geographically anisotropic.     

浅海水域水平扩散系数的推算研究

本文根据拉格朗日流与欧拉流自相关系数的相似关系,用渤中8号平台1987年1月和8月的实测资料,分别推算了水平扩散系数。推算结果表明:研究长时间水平扩散时,把潮流看作湍流,所求的扩散系数实际上是潮流扩散系数,其值在10~6cm~2/s范围内;研究短时间水平扩散时,把潮流看作平流,用富里叶变换的长周期合成值从实测值中扣除,所求的扩散系数消除了长周期潮流部分,可认为是湍流扩散,其值在10~4cm~2/s范围内。     

Seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean based on WHOI flux product

The mean seasonal variability of turbulent heat fluxes in the tropical Atlantic Ocean is examined using the Woods Hole Oceanographic Institution(WHOI) flux product.The most turbulent heat fluxes occur during winter seasons in the two hemispheres,whose centers are located at 10°~20°N and 5°～15°S respectively.In climatological ITCZ,the turbulent heat fluxes are the greatest from June to August,and in equatorial cold tongue the turbulent heat fluxes are the greatest from March to May.Seasonal variability of sensible heat flux is smaller than that of latent heat flux and mainly is dominated by the variations of air-sea temperature difference.In the region with larger climatological mean wind speed(air-sea humidity difference),the variations of air-sea humidity difference(wind speed) dominate the variability of latent heat flux.The characteristics of turbulent heat flux yielded from theory analysis and WHOI dataset is consistent in physics which turns out that WHOI's flux data are pretty reliable in the tropical Atlantic Ocean.     

Determination of characteristics of atmospheric motions from satellite multiwave remote sensing data

A method of determination of atmospheric dynamic characteristics from the data of remote sensing from a geostationary satellite is described. The method is based on the use of inhomogeneities in the concentration field of a conservative additive as tracers and on the application of correlation-extreme algorithms. Unlike the common methods used abroad, this method is able to determine not only the vector field of wind velocity but also the coefficient of turbulent diffusion and vorticity. Results of computations of the fields of the horizontal component of wind velocity and the effective coefficient of horizontal mesoscale turbulent diffusion from the Meteosat-8 SEVIRI water-vapor channel data are presented. It is shown that the average values of the effective coefficient of mesoscale horizontal turbulent diffusion in the areas with a predominantly turbulized air-mass motion are 1.5 times greater than in the areas where a laminar motion dominates. Specific features of the calculated values of the upper-troposphere dynamic characteristics in different stages of the North Atlantic TC Helene (September 2006) are analyzed.     

热带外太平洋通过海洋过程对热带太平洋的影响

利用MOM2海洋环流模式分别研究了年际和年代际尺度上热带外太平洋通过海洋过程对热带太平洋的影响.利用1945~1993年COADS资料的表面通量强迫海洋模式,积分46 a作为模式控制试验.取热带外太平洋海表面强迫为气候值做敏感性试验.将控制试验结果减去敏感性结果就可以得到热带外太平洋通过海洋过程对热带太平洋的影响.结果表明,年际尺度上,主要是海洋波动过程起作用,但总的海洋过程的影响较小.年代际尺度上,主要是副热带环流输送起作用,其中包括平均环流输送的温度异常以及异常环流输送的平均温度,并且后者贡献相对较大.年际和年代际尺度上,热带太平洋的温度异常主要发生在密度跃层附近.研究发现热带外南太平洋对热带和热带外太平洋之间的水量交换有影响,而热带外北太平洋的影响较弱.     

On the use of variable exchange coefficients in the algorithm of a four-dimensional analysis of observations

The use of variable exchange coefficients in the telescopic dynamico-stochastic model is suggested. Through the use of data compiled in the course of a transatlantic survey, we show that consideration of the space-time variability of horizontal exchange coefficients helps to improve the quality of hydrophysical field modelling.Translated by Vladimir A. Puchkin     

海表Ekman流不稳定性致新型次级环流

海洋上混合层中的次级环流可通过物质和能量的垂直输运和混合过程把海洋表层的热量、动量与物质携带到次表层,对海洋上层次级环流生成机制的研究可以丰富对上层海洋的理解和认识。文中利用线性稳定性理论讨论了经典海表Ekman流的不稳定性,提出Ekman流的不稳定性可生成一种新型的次级环流。这种次级环流的空间尺度与雷诺数、Ekman流的垂向衰减速率、水平湍黏性系数与垂向湍黏性系数比值等密切相关,尺度范围从数十米到数千米。数十米量级的次级环流其垂向结构以及次级环流流轴与主流场偏角都与Langmuir环流的特征极为相似,是Langmuir环流形成机制的一种新解释。千米量级的次级环流能够解释黄海浒苔的条带分布。此外,所得次级环流的流轴与主流之间的偏角与科氏力有显著关系,北半球次级环流流轴偏向主流左侧,南半球反之。     

The influence of the spatial heterogeneity of vegetation cover and surface topography on vertical CO<Subscript>2</Subscript> fluxes within the atmospheric surface layer

The influence of the spatial heterogeneity of vegetation cover and topography on CO₂ fluxes in the atmospheric surface layer is estimated using a two-dimensional (2D) hydrodynamic model of turbulent exchange. A ~4.5-km-long profile that crossed a hilly area with a mosaic vegetation cover in Tula region was selected for model experiments. During the first experiment, a wind field and vertical fluxes were calculated by the 2D model for the entire selected profile with respect to the horizontal heterogeneity of the vegetation cover and surface topography. In the second experiment, the profile was considered an assemblage of elementary independent homogeneous segments; for each of them, vertical fluxes were calculated by the 2D model with the assumption of ‘zero’ horizontal advection, i.e., the required functions are independent of the horizontal coordinates. The influences of any boundary effects that appear at the interface between the different vegetation communities and at topographical irregularities on the turbulent regime are ignored in this case. For the profile selected, ignoring the horizontal advection, disturbances in the wind field that appeared at surface topography irregularities, and boundaries between different vegetation communities can lead to a 26% underestimation of the total CО₂ absorption by the ground surface on a clear sunny day under summer weather conditions.     

Numerical experiment on the computation of the equatorial circulation on the basis of a conservative model

A finite-difference system of motion equations for a baroclinic ocean with an irregular bottom is developed on the basis of the box method and the method of indefinite coefficients. The numerical model is shown to possess the property of conserving momentum, mass, and energy. In the case of barotropic motion, the finite-difference scheme retains potential enstrophy. A numerical experiment on the adaptation of hydrophysical fields in the Equatorial Atlantic in summer was carried out within the framework of the model developed. We managed to obtain a series of features of the equatorial circulation when the coefficients of turbulent exchange and diffusion were small enough.Translated by Mikhail M. Trufanov.     

Response of data from numerical modelling of the Equatorial Atlantic circulation to fluctuations of turbulence coefficients

A numerical model for ocean thermohydrodynamics is considered whose difference scheme permits a number of linear and quadratic invariants to be retained. The model is used as the basis for adaptive computations in the Equatorial Atlantic ocean. Model equations were integrated using different values of the coefficients of diffusion and momentum turbulent exchange. It has been shown that variations of these coefficients strongly influence the intensity of jet streams and the structure of the thermocline.Translated by Vladimir A. Puchkin.     

Fine structure of the temperature field and the transfrontal exchange in the East Kamchatka current

CTD data are used to study the relationship between the temperature field fine structure and the location of the frontal zones and synoptic eddies in the region adjacent to the eastern coast of the Kamchatka peninsula. High levels of fine structure activity were observed in the frontal zone of the East Kamchatka current and in the peripheries of anticyclonic eddies. Estimates of the coefficient of the horizontal turbulent exchange and the transfrontal (lateral) heat flux are derived.Translated by Mikhail M. Trufanov.     

Horizontal variability in chlorophyll fluorescence and potential temperature

Chlorophyll fluorescence and temperature were measured with a horizontal resolution of 4 m on two isopycnals and two isobars along a 1000 km meridional transect in the eastern North Pacific. Probability density functions (PDFs) of the magnitude of fluctuations in temperature and fluorescence are compared at each of a large range of length scales. While they are nearly identical at larger scales, the shapes of the PDFs of fluorescence and temperature differ significantly at small scales (∼1 km and less). This difference may indicate that at these scales, temperature and fluorescence distributions are controlled by distinct mechanisms. By comparing the phase of wavelet transforms of each of these two tracers, the tendency for temperature and fluorescence gradients to line up is investigated over a large range of spatial scales. At horizontal length scales of order 10 km and larger, the wavelet phase difference between temperature and fluorescence tends to be close to 0° or 180°—that is, the gradients tend to align, either in phase or 180° out of phase. At smaller scales, the distribution of phase difference on isopycnals is uniform—there is no tendency for gradients to coincide. Simple stirring models demonstrate that the locations of enhanced gradients in all tracers would be expected to coincide where the strain has been greatest. However, the directions of enhanced gradients formed in this way may be either parallel or antiparallel, depending on initial conditions and on the direction of the strain. These analyses suggest the horizontal distributions of temperature and fluorescence at large scales were both governed by advective processes. At intermediate scales, of order 1–10 km, a renovating wave model suggests that gradient alignment could be destroyed by turbulent diffusion or by rapid local phytoplankton growth.     

Estimating the characteristics of the vertical turbulent viscosity in the upper 200-m layer of the Black Sea

The influence of high vertical velocity gradients in the Black Sea Rim Current on the intensity of the vertical turbulent exchange is demonstrated on the basis of numerical modeling based on CTD data. The vertical turbulent exchange is confirmed by the anomalous distribution of the hydrochemical parameters in the redox layer. A system of equations for the kinetic energy of the turbulence and dissipation rate (k-? model) is used for the calculation of the coefficient of the vertical turbulent viscosity (diffusivity).