A hydrothermodynamic quasi-isopycnic model of the ocean thermocline

The results of a numerical experiment on the formation of the large-scale circulation and the main thermocline in the temperate latitudes of an ocean at steady external factors are discussed. A multilayer model [1] is used which involves the upper mixed layer (UML). The boundaries of the areas where the internal layers reach the UML are calculated. The zones where seawater is entrapped from the thermocline to the UML are revealed, as well as the subduction zones where seawater is brought from the UML to the internal layers and moves there, ventilating the thermocline.Translated by Mikhail M. Trufanov. UDK 551.465.     

Modelling of the upper mixed layer in the Tropical Atlantic

A method for the computation of the spatial-temporal variability of the upper mixed layer (UML) within the framework of a model for the multilayer ocean is proposed. Using a three-layer ocean (UML, thermocline, and abyssal regions) as an example, the formation of the UML topography from the state of rest and the current and temperature fields in the Tropical Atlantic are considered.Translated by Mikhail M. Trufanov.     

Modelling of upwelling and downwelling in the ocean

Numerical experiments on the reconstruction of upwelling and downwelling at the eastern boundary of the ocean were carried out in the framework of a multilayer model of the ocean involving the upper mixed layer (UML). The peculiarities of these phenomena when they are formed and attenuated owing to the strong intensification and abatement of the longshore wind have been studied. It is shown that cold waters are always involved from the thermocline to the UML during upwelling. In downwelling, this occurs as a rule. However, during upwelling the abatement of the wind may result in subduction —the inflow of warm waters from the UML to the thermocline.Translated by Mikhail M. Trufanov.     

Upwelling into the thermocline of the Pacific Ocean

The established “island rule” and the recently introduced “separation formula” are combined to yield an analytical expression for the total upwelling into the thermocline in the Pacific. The combination of the two is achieved with the use of a hybrid model containing a stratified upper layer, a thick (slowly moving) homogenous intermediate layer and an inert lower layer. Both the upper and the intermediate layers are subject to diabatic cooling and heating (which need not be specified) and there is an exchange of mass between the two active layers. An attempt is made to examine the above analytical (hybrid) model numerically. Ideally, this should be done with a complete two-and-a-half layer model (with upwelling and downwelling), but such a model is much too complex for process-oriented studies (due to the required parameterization of vertical mixing). Consequently, we focus our attention on verifying that the separation formula and the island rule are consistent with each other in a much simpler, layer-and-a-half model (without upwelling). We first verified that the new “separation formula” provides a reasonable estimate of the wind-induced transport in an island-free basin. We then compare the wind-induced transport predicted by the separation formula and the island rule in an idealized basin containing an island. We show that in these idealized situations the two methods give results that are consistent with each other and the numerics. We then turned to an application of the (hybrid) two-and-a-half layer model to the Pacific where, in contrast to the idealized layer-and-a-half models (where the two methods address the same water mass), the two methods address two different water masses. While the separation formula addresses only thermocline water (σ_θ<26.20), the island rule addresses all the water down to 27.5σ_θ (i.e., both the upper and intermediate layer). This is why the application of the two methods to the Pacific gives two different results — an application of the formula gives zero warm water transport whereas an application of the island rule gives 16 Sv. Namely, the difference between the amount predicted by the island rule (16 Sv) and the amount predicted by the separation formula (zero) enters the Pacific as intermediate water and is then somehow upwelled into the thermocline. The upwelling should take place north of the southern western boundary currents separation (40°S).     

浅海双跃层脉冲声传播

利用在东海测量的双跃层声速剖面和修改的单跃层声速剖面,数值模拟了2种跃层条件下不同收发深度声脉冲传播的波形。模拟结果表明,当声源或接收器位于上混合层时,信号波形在2种条件下都出现梳状多途结构。当声源和接收器都位于下混合层时,信号波形在2种条件下均相似。当声源位于中间均匀层时,信号波形在除上混合层以外的4层都有显著差异。用简正波的深度-简正波号域的幅度和相应的群速度解释了双跃层和单跃层声速剖面条件下信号波形特点以及异同的原因。     

Inertial currents in the northern North sea

Current profiles were measured in the northern North Sea during the autumnal breakdown of stratification (September and October) in 1998. The site was in 110 m of water and the depth-averaged M₂ tidal current amplitudes were about 0.15 m s⁻¹. The surface and bed mixed layers were initially well separated. The measurements were made principally with Acoustic Doppler Current Profilers (ADCP) which gave good coverage of the majority of the water column.During a two-month period several episodes of inertial currents were observed, exhibiting a range of responses some of which corresponded very closely to that predicted by theory. The structure of the inertial currents was primarily first mode baroclinic, with no inertial energy in the depth-averaged current. This implies that the currents in the lower layer are strongly linked to those in the surface layer and also that dissipation could be generated by bed friction, but the nature of the link is unclear. The level of least motion coincided with the thermocline. Since the currents in the upper and lower layers are 180° out of phase, large shears can occur across the thermocline; occasionally the bulk Richardson number determined with a four-metre vertical resolution was less than one.Turbulence measurements suggest that when large inertial current shears are present across the thermocline, which exceed the buoyancy frequencies, then mixing within and across the thermocline is significant. Future experiments should concentrate on enhanced dissipation measurements around the thermocline and higher spatial resolution time series measurements of current and density.     

Observation and modelling of the variability of the Arabian Sea upper layers during the development of the SW monsoon in 1988 and 1989

Experimental data on the vertical structure of theT, S temporal variations in the upper 1000 m layer of the Arabian Sea during the inter-monsoon period from April to June are reported. Variations in the upper mixed layer (UML) thickness and temperature distributed horizontally are considered. The local UML model was used to compute these variations from the atmospheric influence preset from observations.Translated by Mikhail M. Trufanov.     

Research on the Propagation Acting of the Equatorial Planetary Waves on the Western Equatorial Pacific Warm Pool Heat

1 IntroductionIn the Equatorial Pacific, due to the difference between the atmospheric circulation and air-sea interaction, the near-surface seawater heat structure in the eastern and western Pacific presents two ℃obviously different characteristics: warm pool ( > 28 ) in the western equatorial Pacific and cold ℃tongue ( < 24 ) in the eastern equatorial Pacific. The water bodies of these two heat structures would give rise to change in spatial distribution under the action of the equato…     

与南沙深水区温跃层有关的海水平均温度的分布特征

在确定温跃层三要素 (深度 (上界深度 )、厚度和强度 )及测站温度垂直最大梯度的基础上 ,分别计算了南沙深水测站 (水深大于 1 0 0 0m)在温跃层上界深度层范围内的平均温度、在温跃层下界深度以下自 3 0 0m层至 80 0m层之间的平均温度。分析表明 ,在温跃层上界深度范围内 ,海水平均温度的水平分布明显显示出低温海水自南沙的西北部向东南部缓慢推进之势 ,似是东北季风驱动的结果。温度垂直梯度越大 ,它在垂直方向上阻碍上层海水的热量往深层扩散的能力就越强。     

A three-layer model for the thermal structure in the Huanghai Sea

A one-dimentional three-layer model for the thermal structure in the Huanghai Sea is presented in this study, me model consists of the upper mixed layer caused by heating and wind mixing, the lower mixed layer driven by tidal mixing, and the thermocline with certain thickness. The entrainment velocities of the upper and lower layers are obtained respectively. The results show that the model is capable of describing the development and decline processes of the seasonal thermocline in the Huanghai Sea, simulating successfully the Huanghai Sea Cold Water Mass, the nearshore front and surface cold water off North Jiangsu and explaining reasonably their formation mechanisms as well as the strong thermocline off Qingdao. It is suggested that the tidal mixing plays key role in the formation of the nearshore front off North Jiangsu and the strong thermocline off Qingdao. The wind mixing and the tidal mixing make the lower layer water with high nutrients go up to the upper layer. This physical process may be sig     

1997年11月南沙群岛调查海区的跃层特征

本文对１９９７年１１月南沙海区综合考察的标准层资料运用三次样条插值函数法,计算了调查海区的温、盐两种跃层所处的深度及各自的厚度和强度,并进行了相应的分析,特别对季节性温、盐跃层的示性特征,进行了讨论。分析研究发现：所有测站均存在温跃层和盐跃层,其中多跃层超过５０％,跃层的强度和厚度呈相对应的关系,即厚度大（小）的地方强度小（大）。还用连续观测资料对温度日跃层进行了简单的描述,并分析了日温跃层特笥与     

潮汐作用下渤海温跃层波动与起伏的数值研究

研究了潮汐(四大分潮 M₂,S₂,K₁,O₁同时输入)作用下渤海温跃层起伏与波动的三维数值模型(将海洋分为3层,即上混和层、跃层和下混和层),揭示了整个海区温跃层上界面处跃层起伏(在文中指每个时刻跃层波高的周期平均值)的地理分布及叠加在起伏之上的潮周期波动的时空变化,模拟出跃层波动与实测基本一致.结果发现大振幅的跃层波动均发生在海峡及近海地形突变之处.一般界面波动的波高大于甚至远远大于同一位置的表层潮波.从位相以及周期来看,潮波和跃层上下界面波动相互之间,有些海域一致,有些地方则相差甚远.跃层上界深度及厚度的梯度,对跃层起伏分布有一定的影响.跃层起伏还可能与海岸海底摩擦有关.     

On the origin of the Tsushima Warm Current Water

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Distribution Characteristics of Mean Seawater Temperature Related to the Thermocline in the Deep-Water Area of Nansha

On the bisis of determining the there elements of themocline ( depth [upper bound depth ], thickness and intensity ) and the maximum vertical temperature gradient of the surveying station, the paper calculates the mean temperature of the Nansha deep-water surveying station within the upper-bound depth layer of thermocline and the mean temperature below the lowerbound depth of thermocline between the 300m and 800m layers,respectively. Analysis indicates that the horizontal distribution of mean seawater temperature shows a distinct trend of the lowtemperature seawater slowly moving from tbe northeast to the southeast of Nansha,which seems to have been driven by the Northeast Monsoon. The larger the vertical temperature radient is, the greater is its capability of preventing the heat of the upper seawater from diffusing into the deeper layers on the vertical direction.     

Modelling of the generation and evolution of the cold intermediate layer in the Black Sea

This paper discusses the results of a numerical experiment on modelling the seasonal variability of the water circulation and temperature/salinity fields in the Black Sea. A multi-layered quasi-isopycnic model is used based on primitive equations and incorporating the upper mixed layer (UML). It is shown that during springtime warming, relatively cold layers emerge in some areas, due to subduction, from the UML, which then spread virtually over the entire basin and persist until they become absorbed by the rapidly deepening UML during the period of cooling in winter. Translated by Vladimir A. Puchkin.     

Exponential model of the seasonal thermocline

An exponential model of the seasonal thermocline is suggested within the framework of an integral hydrodynamic model of the upper ocean. The seasonal thermocline is discriminated as a boundary layer of finite thickness against the background of an asymptotic boundary layer described by an exponent. A self-similar distribution of the dimensionless temperature versus dimensionless depth is found. Its comparison with the dependence obtained previously (cubic parabola) provides a deviation of 10%. Thus, the exponential model of the seasonal thermodcline describes perfectly the temperature-depth distribution using field data.Translated by Mikhail M. Trufanov.     

Effect of the Internal Tide on Acoustic Transmission Loss at Midfrequencies

Nonlinear internal waves are a common event on the continental shelf. The waves depress the high-gradient region of the thermocline and thicken the surface mixed layer with consequent effect on acoustic propagation. After the waves have passed, it may take several hours for the thermocline to rise to its prewave level. To examine the effect of the rising thermocline, oceanographic and acoustic data collected during the 2006 Shallow Water Experiment (SW06) are analyzed. Midfrequency acoustic data (1.5–10.5 kHz) taken for several hours at both fixed range (550 m) and along a tow track (0.1–8.1 km) are studied. At the fixed range, the rising thermocline is shown to increase acoustic intensity by approximately 5 dB . Along the tow track, the transmission loss changes 2 dB for a source–receiver pair that straddles the thermocline. Using oceanographic moorings up to 2.2 km away from the acoustic receiver, a model for the rising thermocline is developed. This ocean model is used as input to a broadband acoustic model. Results from the combined model are shown to be in good agreement with experimental observation. The effects on acoustic signals are shown to be observable, significant, and predictable.      

A PARAMETRIC MODEL FOR THERMAL STRUCTURE FEATURES OF THE OCEAN UPPER LAYER

Based on the non-dimensional general function for the thermal structure features presented by S. A. Kitaigorodsky et al. (1963, 1965)[10,11]. this paper tries to establish semi-empirical and semi-theoretical models bfor the thickness of the upper homogeneous layer of the ocean, thermocline intensity and lower oundary depth of thermocline by consecutive observations from 159 stations in the Bohai Sea,Huanghai Sea and East China Sea in the warm half of the years from 1957 to 1964 and the heat budget at the sea surface computed with the simplified computing formulae proposed by Wang (1983)[22]. This model indicates the main factors forming the thermal structure features in the upper layer of the ocean and their function. With the model, one can directly use the sea surface temperature, air temperature and wind speed to compute the thermal feature in the upper layer of the ocean.     

Characteristics and variability of the Indonesian throughflow water at the outflow straits

Property structure and variability of the Indonesian Throughflow Water in the major outflow straits (Lombok, Ombai and Timor) are revised from newly available data sets and output from a numerical model. Emphasis is put on the upper layers of the Indonesian Throughflow that impacts the heat and freshwater fluxes of the South Equatorial Current in the Indian Ocean. During the April–June monsoon transition the salinity maximum signature of the North Pacific thermocline water is strongly attenuated. This freshening of the thermocline layer is more intense in Ombai and is related to the supply of fresh near-surface Java Sea water that is drawn eastward by surface monsoon currents and subject to strong diapycnal mixing. The freshwater exits to the Indian Ocean first through Lombok Strait and later through Ombai and Timor, with an advective phase lag of between one and five months. Because of these phase lags, the fresher surface and thermocline water is found in the southeast Indian Ocean from the beginning of the monsoon transition period in April through until the end of the southeast monsoon in September, a much longer time period than previously estimated.     

Exponential leap-forward gradient scheme for determining the isothermal layer depth from profile data

Two distinct layers usually exist in the upper ocean. The first has a near-zero vertical gradient in temperature (or density) from the surface and is called the isothermal layer (or mixed layer). Beneath that is a layer with a strong vertical gradient in temperature (or density), called the thermocline (or pycnocline). The isothermal layer depth (ILD) or mixed layer depth (MLD) for the same profile varies depending on the method used to determine it. Also, whether they are subjective or objective, existing methods of determining the ILD do not estimate the thermocline (pycnocline) gradient. Here, we propose a new exponential leap-forward gradient (ELG) method of determining the ILD that retains the strengths of subjective (simplicity) and objective (gradient change) methods and avoids their weaknesses (subjective methods are threshold-sensitive and objective methods are computationally intensive). This new method involves two steps: (1) the estimation of the thermocline gradient G _th for an individual temperature profile, and (2) the computation of the vertical gradient by averaging over gradients using exponential leap-forward steps. Such averaging can filter out noise in the profile data. Five existing methods of determining the ILD (difference, gradient, maximum curvature, maximum angle, and optimal linear fitting methods) as well as the proposed ELG method were verified using global expendable bathythermograph (XBT) temperature and conductivity–temperature–depth (CTD) datasets. Among all the methods considered, the ELG method yielded the highest skill score and the lowest Shannon information entropy (i.e., the lowest uncertainty).