Beam forming on bottom-interacting tow-ship noise

Ship noise received on a horizontal array towed behind the ship is shown to be useful as a potentially diagnostic tool for estimating local acoustic bottom properties. In numerical simulations, tow-ship noise which bounces off the bottom is processed on a beamformer that shows the arrival angles; the beamformer output is readily interpreted by relating it to the Green's function of the acoustic wave equation. Simple signal processing is shown to be sufficient to extract the propagation angles of the "trapped" (i.e., propagating) modes of the acoustic waveguide. By relating the trapped modes to a basic geophysical model of the bottom, one can predict acoustic-propagation conditions for a particular bottom-interacting ocean acoustic environment.     

A continuum model for the linear wave propagation in ice-covered oceans: An approximate solution

In order to model the wave-in-ice climate on a geophysical scale, a continuum viscoelastic model has been developed [Wang, R., Shen, H.H., 2010. Gravity waves propagating into an ice-covered ocean: a viscoelastic model. J. Geophys. Res. 115, C06024. doi:10.1029/2009JC005591]. In this model, two modes were identified to be dominant, each for the low or high elasticity range, respectively. In the intermediate elasticity range, both modes have comparable attenuation rates and wave numbers, and they could be co-dominant. Inspired by the Eigenfunction Expansion Matching Method, this paper presents an approximate approach to solve the wave propagation characteristics in the whole physical range of elasticity. A monochromatic wave propagating from semi-infinite open water into semi-infinite ice-covered water is considered. Only two transmitted wave modes are included in the eigenfunction expansions for the ice-covered water. These two modes correspond to the dominant mode under relatively low or high elasticity, respectively. Evanescent wave modes in open water are ignored. By minimizing the matching errors, the least square solution is obtained. For the pure elastic ice cover, the results are compared with the exact solution from the thin elastic plate model. The comparison is in good agreement when the wave period is larger than 10 s. Mild discrepancies exist when the period is smaller than 10 s. The present model provides the simplest way to describe wave propagation characteristics in different types of ice covers.     

Fast coupled-mode approximation for broad-band pulse propagation ina range-dependent ocean

An approximation method is proposed for the prediction of broad-band acoustic signals propagating in range-dependent ocean environments. The method is based on the one-way coupled-mode approach and uses second-order frequency expansions of eigenvalues, eigenfunctions, and coupling coefficients about the central frequency of the source. Exploiting analytic expressions for the frequency derivatives of eigenvalues and eigenfunctions, their frequency behavior over the source bandwidth is described from the solution of the vertical eigenvalue problem at the central (reference) frequency. The expansion obtained for the coupling coefficients enables their approximate evaluation at frequencies other than central in terms of reference quantities and, thus, bypasses the need for evaluative eigenfunctions in the intermediate range segments for these frequencies. The method is applied to a 600-km range-dependent section from the Thetis-2 tomography experiment in the western Mediterranean sea. A sufficient degree of accuracy is obtained, particularly for the low- and intermediate-order modes, corresponding to the intermediate and late part of the arrival pattern in the time domain. The approximation is faster by two orders of magnitude than the exact broad-band coupled-mode calculation     

The propagation of an acoustic pulse in a near-ground atmospheric waveguide

A wave theory of propagation of an acoustic pulse in a moving stratified atmospheric layer above the ground with a finite impedance of an underlying ground surface is developed. The shapes of acoustic signals in a near-ground atmospheric waveguide, which are formed due to temperature inversion and a vertical shear of the wind velocity, are calculated based on this theory. These signals are compared with those measured during the experiments where vertical profiles of the wind velocity and temperature in an atmospheric boundary layer have been continuously controlled using a sodar, a temperature profile meter, and acoustic anemometers or thermometers mounted on a 56-meter-high mast. The joint action of a near-ground acoustic waveguide, the impedance of the underlying surface, and a vertical layered structure of the boundary atmospheric layer on a signal shape far from the acoustic source are studied.     

Effects of internal waves on sound pulse propagation in the Straitsof Florida

An unexplained result of broad-band transmission experiments made more than ten years ago by DeFerrari in the Straits of Florida (center frequency ~500 Hz, bandwidth ~100 Hz, water depth ~200-m, range ~20 km) is that the measured pulse response functions failed to show the expected multipath replicas of the transmitted pulse and instead were smeared into a single broad cluster (duration ~50-~350 ms) in which the unresolved multipaths fluctuated rapidly in geophysical time (coherence time ≪12 min) leaving only a relatively stable envelope that is useful for oceanographic inversion. It is demonstrated here that the effects of internal waves on sound pulse propagation in the Straits of Florida can explain these observed results, and it is suggested that similar instabilities of acoustic multipaths due to internal waves are to be expected in other shallow-water propagation conditions. The demonstration is based on numerical simulations with the broad-band UMPE acoustic model that includes multiple forward scattering from volume inhomogeneities induced by internal wave fluctuations that are described by a broad spectrum of excitation. The simulated temporal variability, stability, and coherence of acoustic pulse arrivals are displayed on geophysical time scales from seconds to many hours and are qualitatively in agreement with the measured data in the Straits of Florida     

Low-frequency bottom loss

The shallow refracted path through sea floor sediments plays a significant role in the transmission of acoustic energy at low frequencies. For bottom grazing angles of 90/spl deg/ to 25/spl deg/, low-frequency acoustic energy was observed to come from reflected paths. For bottom grazing angles of 25/spl deg/ to 10/spl deg/ the dominant source of low-frequency acoustic energy is from shallow refracted paths through the sediments. At angles less than 10/spl deg/, low-frequency acoustic energy is received from both the refracted and the reflected paths. The refracted path is possible because of the positive gradient within the sediment. The sudden emergence of the refracted arrival is related to the overall sound path length in the sediment and sediment absorption of sound. Since sediment absorption is directly proportional to frequency, only low-frequency energy is transmitted via this path. The refracted path may well exist where unconsolidated sediments of at least a few hundred feet are present.     

Manganese fluxes to the oceans

Application of a simple model describing regional variations in the contents of manganese and associated minor metals in deep-sea sediments suggests that solid manganese phases are being removed from the <0.5 μm fraction of seawater at ～1–7 · 10¹²g yr^?1 in excess of the rate of stream-supplied manganese. This flux is consistent with: (1) the relative rates of sediment accumulation in the Atlantic and Pacific Oceans; (2) the contrast between the oceanic residence time of manganese calculated from stream-supply data (14 · 10³ yr) and from the flux of manganese precipitating in marine sediments or as manganese nodules (0.38–2.4 · 10³ yr); (3) the surplus mass of manganese revealed by geochemical balance calculations (22.9 · 10²g). On this basis excess manganese is accumulating in deep-sea sediments at 0.2–2.0 · 10^?6 g cm^?2yr^?1. Manganese supplied to the upper layers of marine sediments by diagenesis has been evaluated with the aid of vertical advection—diffusion—reaction models. The calculated diagenetic flux of manganese at the sediment surface in a near-shore environment is in agreement with the known accretion rate of manganese deposits (1.7 · 10^?2 g cm^?2 10^?3 yr^?1) and the regionally variable flux over the area assessed is consistent with the presence or absence of manganese nodules at or near the water-sediment interface. The diagenetic flux at the surface of deep-sea sediments has been calculated at 0.7 · 10^?4 g cm^?2 10^?3 yr^?1 when the upper, oxic, zone of the sediment is ～20 cm thick. A limiting factor on the in situ production flux of dissolved manganese in deep-sea sediments appears to be the availability of reducing agents for manganese dissolution rather than the rate of downward transport of manganese-rich sediment to a reaction boundary where dissolution takes place. Various estimates of the rate of upward-migrating manganese suggest that manganese precipitates in the oxic zone with a rate constant of ～10^?7 sec^?1 with the result that diagenetic processes cannot supply the flux of excess manganese through more than ～0.25 m of oxic sediment. However, estimates of the flux of manganese to the oceans by submarine volcanic processes (0.79–1.1 · 10¹²g yr^?1) are similar to the surplus mass of manganese detected by geochemical balance calculations (0.7 · 10¹²g yr^?1). If submarine hydrothermal solutions provide only 10% of this excess then their computed discharge rate (39 g cm^?2 yr^?1) and residence time in the upper layer of oceanic crust (130,000 yr) agree well with these parameters for continental thermal springs.     

Low-frequency sound interaction with a sloping, refracting oceanbottom

The effects of refracting sediments on low-frequency sound propagation in range-dependent oceans are studied with parabolic equation models. The predictions of three sediment sound-speed models for low-frequency propagation are compared. Two factors that result in sediment sound-speed gradients are considered. Variation in static pressure due to the variation in the weight of overlying material causes sediment sound speed to increase with depth. The thermodynamic influence of the ocean results in large sound-speed gradients in a boundary layer in the uppermost layer of the sediment. The associated affects of attenuation on propagation are also considered. Both time-domain and frequency-domain results are presented     

Pelitic matter differentiation in seas and oceans

Pelitic matter is subjected to differentiation at any depth. Filter feeding organisms just accelerate sedimentation of fine particles and do not affect their distribution at the bottom, thus, passively reflecting the content of pelitic fractions in suspended matter.     

Simulating large-scale circulation in seas and oceans

The problem of simulating ocean general circulation is considered using an approach developed by G.I. Marchuk. Most attention is focused on problems associated with the application of multi-component-splitting and adjoint-equation methods and with the parameterization of turbulent-exchange processes. The statement of the problem, an algorithm of its solution, and the results of the four-dimensional temperature and salinity data assimilation in a model of World Ocean hydrodynamics are discussed. This algorithm yields qualitatively reliable results, and its main features are modularity, usability, and the possibility of using efficient implicit schemes.     

Seasonal cooling and blooming in tropical oceans

The relative importance of tropical pelagic algal blooms in not yet fully appreciated and the way they are induced not well understood. The tropical Atlantic supports pelagic blooms together equivalent to the North Atlantic spring bloom. These blooms are driven by thermocline tilting, curl of wind stress and eddy upwelling as the ocean responds to intensified basin-scale winds in boreal summer. The dimensions of the Pacific Ocean are such that seasonal thermocline tilting does not occur, and nutrient conditions are such that tilting might not induce bloom, in any case. Divergence at the equator is a separate process that strengthens the Atlantic bloom, is more prominent in the eastern Pacific, and in the Indian Ocean induces a bloom only in the western part of the ocean. Where western jet currents are retroflected from the coast off Somalia and Brazil, eddy upwelling induces prominent blooms. In the eastward flow of the northern equatorial countercurrents, positive wind curl stress induces Ekman pumping and the induction of algal blooms aligned with the currents. Some apparent algal bloom, such as that seen frequently in CZCS images westwards from Senegal, must be due to interference from airborne dust.     

全球大洋季节内尺度上海-气相互作用特征分析

判定局地海-气相互作用的特征对海-气耦合模式中应用哪种形式的“强迫模拟”具有重要指导作用。本文根据海表热通量异常与海表温度异常及海表温度变率之间的相关关系,对全球大洋季节内尺度上的海-气相互作用特征进行了综合分析。结果表明:(1)南、北半球亚热带地区海-气相互作用的特征主要表现为大气对海洋的强迫,且在夏季(北半球为6—8月,南半球为12—翌年2月)强迫作用的范围最大,冬季强迫作用的范围最小;(2)赤道中、东太平洋及赤道大西洋地区海-气相互作用的特征全年表现为海洋对大气的强迫,印度洋索马里沿岸、阿拉伯海以及孟加拉湾地区仅在6—8月表现出海洋强迫大气的现象,而孟加拉湾则在9—11月表现为大气强迫海洋;(3)45°N(S)以上的高纬度地区海表温度的异常和变率无法用局地热通量的交换来解释,这是因为该区域海表温度的变化主要由平流等海洋内部动力过程决定,因此海-气之间在季节内尺度上的相互作用不明显。在某些海区,季节内尺度上的海-气相互作用关系与季节以上时间尺度的这种关系可能会有明显不同。     

Meso-scale available gravitational potential in the world oceans

The pitfalls of applying the commonly used definition of available gravitational potential energy （AGPE） to the world oceans are re-examined. It is proposed that such definition should apply to the meso-scale problems in the oceans, not the global scale. Based on WOA98 climatological data, the meso-scale AGPE in the world oceans is estimated. Unlike previous results by Oort et al. , the meso-scale AGPE is large wherever there is a strong horizontal density gradient. The distribution of meso-scale AGPE reveals the close connection between the baroclinic instability and the release of gravitational potential energy stored within the scale of Rossby deformation radius.     

海洋及其上空大气中有机磷酸酯的研究进展

基于全球海洋及其上空大气中关于有机磷酸酯(OPEs)的数据,分析了目前OPEs在全球海洋及其上空大气的分布特征、影响因素以及当前研究存在的不足。总结发现,海水中的OPEs主要来自河流输送,且浓度分布特征表现为由近及远、由浅及深逐渐递减。磷酸三(2-氯乙基)酯(TCEP)、磷酸三(1-氯-2-丙基)酯(TCPP)和磷酸三(1,3-二氯异丙基)酯(TDCPP)三种卤化OPEs是海水中主要污染物;输入到海水中的OPEs经过颗粒沉降等作用沉积到海洋沉积物中,随之,沉积物中的OPEs可能反析出或直接累积,在海洋沉积物中形成一个大的OPEs储存库。分析北太平洋到北冰洋表层沉积物中OPEs的浓度发现,从白令海峡到北冰洋,随着纬度的增加OPEs的浓度也普遍增加,且相对于非卤化OPEs,卤化OPEs更易被运输到偏远海域。总有机碳(TOC)与大洋沉积物中OPEs的浓度无相关性,但与近海海洋沉积物中OPEs的浓度呈正相关,TCEP和磷酸三异丁酯(TiBP)为海洋沉积物中主要污染物;海洋上空大气与水体中的OPEs是不可分割的,海洋上空大气中的OPEs一部分通过大气沉降进入海水,一部分继续迁移到更偏远区域,气团...