Parameterization of Wave Breaking Probability and Whitecap Coverage     

李晶于定勇  刘华兴 《中国海洋工程》2006,20(3):411-418

1 .Introduction Wave breaking and associated whitecapping have long beeninteresting due totheir close relationto many fields of ocean study,including air-sea interaction,remote sensing,ocean engineering,aswell as wave dynamics .The breaking probabilityBan…  相似文献   

Age, growth, and condition of European eel (Anguilla anguilla) from six lakes in the River Havel system (Germany)     

Simon  Janek 《ICES Journal of Marine Science》2007,64(7):1414-1422

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Elucidating the dynamics and mixing agents of a shallow fjord through age tracer modelling     

Karin E. Gustafsson  Jrgen Bendtsen 《Estuarine, Coastal and Shelf Science》2007,74(4):641

The mixing agents and their role in the dynamics of a shallow fjord are elucidated through an Eulerian implementation of artificial tracers in a three-dimensional hydrodynamic model. The time scales of vertical mixing in this shallow estuary are short, and the artificial tracers are utilized in order to reveal information not detectable in the temperature or salinity fields. The fjord's response to external forcing is investigated through a series of model experiments in which we quantify vertical mixing, transport time scales of fresh water runoff and estuarine circulation in relation to external forcing.Using age tracers released at surface and bottom, we quantify the time scales of downward mixing of surface water and upward mixing of bottom water. Wind is shown to be the major agent for vertical mixing at nearly all depth levels in the fjord, whereas the tide or external sea level forcing is a minor agent and only occasionally more important just close to the bottom. The time scale of vertical mixing of surface water to the bottom or ventilation time scale of bottom water is estimated to be in the range 0.7 h to 9.0 days, with an average age of 2.7 days for the year 2004.The fjord receives fresh water from two streams entering the innermost part of the fjord, and the distribution and age of this water are studied using both ageing and conservative tracers. The salinity variations outside this fjord are large, and in contrast to the salinity, the artificial tracers provide a straight forward analysis of river water content. The ageing tracer is used to estimate transport time scales of river water (i.e. the time elapsed since the water left the river mouth). In May 2004, the typical age of river water leaving the fjord mouth is 5 days. As the major vertical mixing agent is wind, it controls the estuarine circulation and export of river water. When the wind stress is set to zero, the vertical mixing is reduced and the vertical salinity stratification is increased, and the river water can be effectively exported out of the fjord.We also analyse the river tracer fields and salinity field in relation to along estuary winds in order to detect signs of wind-induced straining of the along estuary density gradient. We find that events of down estuary winds are primarily associated with a reduced along estuary salinity gradient due to increased surface salinity in the innermost part of the fjord, and with an overall decrease in vertical stratification and river water content at the surface. Thus, our results show no apparent signs of wind-induced straining in this shallow fjord but instead they indicate increased levels of vertical mixing or upwelling during down estuary wind events.  相似文献   

Toward a generic method for studying water renewal, with application to the epilimnion of Lake Tanganyika   总被引：3，自引：0，他引：3  

Olivier Gourgue  Eric Deleersnijder  Laurent White   《Estuarine, Coastal and Shelf Science》2007,74(4):628

We present a method, based on the concept of age and residence time, to study the water renewal in a semi-enclosed domain. We split the water of this domain into different water types. The initial water is the water initially present in the semi-enclosed domain. The renewing water is defined as the water entering the domain of interest. Several renewing water types may be considered depending on their origin. We present the equations for computing the age and the residence time of a certain water type. These timescales are of use to understand the rate at which the water renewal takes place. Computing these timescales can be achieved at an acceptable extra computer cost.The above-mentioned method is applied to study the renewal of epilimnion (i.e. the surface layer) water in Lake Tanganyika. We have built a finite element reduced-gravity model modified to take into account the water exchange between the epilimnion and the hypolimnion (i.e. the bottom layer), the water supply from precipitation and incoming rivers, and the water loss from evaporation and the only outgoing river. With our water renewal diagnoses, we show that the only significant process in the renewal of epilimnion water in Lake Tanganyika is the water exchange between the epilimnion and the hypolimnion, other phenomena being negligible.  相似文献   

东海区小黄鱼渔业生物学现状的分析   总被引：15，自引：1，他引：15  

林龙山  程家骅 《中国海洋大学学报(自然科学版)》2004,34(4):565-570

以2001年东海区渔业资源监测调查资料为依据，对小黄鱼的体长、体重、生长、死亡等渔业生物学特征及临界年龄等进行了分析研究。结果表明，目前东海区小黄鱼优势体长组为110～130mm，占41．34％；优势体重组为20～40g，占50．91％；总死亡系数为2．05，自然死亡系数为0．58，捕捞死亡系数为1．47，临界年龄为2．18龄。对照东海区小黄鱼生物学特征的历史状况分析，目前东海区小黄鱼个体小型化、低龄化、性成熟提早现象明显，生物学参数发生较大变化。建议在东海区现行资源状态下，小黄鱼的可捕标准应充分考虑其生物学现状加以科学调整。  相似文献   

两参量的海面阻力系数模式的探讨   总被引：4，自引：0，他引：4  

汪炳祥 《海洋与湖沼》1997,28(1):96-103

从风浪的能量平衡方程出发，引进若干风要素与波要素以及波要素之间的定性关系，经演算可导出海面阻力系数（Ｃｐ）或是风速（Ｕ）和波龄（β）或是Ｕ和波高（Ｈ）的函数，然后沿用最小二乘法，终将得出４组１２个回归方程。当β（或β）或Ｈ为某一给定值，惟有Ｕ为唯一参量时，所提各式均可简化为非线性方程：ＣＤ＝ａ＋ｂ，Ｕ＋ｃ．Ｕ＾２；式中ａ，ｂ和ｃ为三个经验系数，就所检验的例子而言，本文的结果与实际的符合前人的为好。  相似文献   

Population Structure and Secondary Production of the Mediterranean Octocoral Lophogorgia ceratophyta (L. 1758)     

M. Mistri 《Marine Ecology》1995,16(3):181-188

Abstract. The gorgonian Lophogorgia ceratophyta thrives in turbid water at Tinetto Rock, La Spezia Gulf, Ligurian Sea. Its age structure suggests that the population is in a steady state; nevertheless, it is difficult to discern whether the main factors controlling this population are biological or event-related. Secondary production was estimated by means of an increment-summation method and yielded 0.54 g ash-free dry weight (AFDW)*m^-1 a^-1. This estimate does not take into account biomass losses due to reproductive output and non-lethal predation. Standing stock biomass was 5.44 g AFDW e m^-2. The annual P/B ratio was 0.10 and turnover time about 10a  相似文献   

柴达木盆地新构造运动主要特征与成因机制   总被引：10，自引：0，他引：10  

杨明慧 《海洋地质与第四纪地质》1997,17(3):71-78

研究表明，在壳幔结构、地球物理背景、沉积物结构、多层关地幔和构造样式等方面，达木盆地与中国东部新生代裂谷类伸展盆地具有可比性，应该归属 展性盆 。盆地伸展和收缩作用相间进行，伸展起因于地幔底辟；而收缩受两人因素影响；（１）盆地伸展作用受相邻造山带反作用诱导的挤压应力；（２）板块碰撞传递的远程板内应力。在此基础邮新的构造期达木盆地演化的“双层模式”，即地幔上隆－地壳伸展；被动挤压＋板内应力－地壳收缩  相似文献   

Determining the age of water and long-term transport timescale of the Chesapeake Bay   总被引：5，自引：0，他引：5  

Jian Shen  Harry V. Wang 《Estuarine, Coastal and Shelf Science》2007,74(4):585-598

The concept of age of water (AW) is applied to the Chesapeake Bay to investigate the long-term transport properties for dissolved substances. A real-time calibrated hydrodynamic Chesapeake Bay model in 3 Dimensions (CH3D), employing a boundary-fitted curvilinear grid, is used for the study. The long-term transport properties, represented by AW, are investigated under the conditions of low river inflow of 1995 and high river inflow of 1996, as well as for constant mean inflows. The influences of freshwater, density-induced circulation, and wind-induced transport on age distribution have been investigated. Model results show that river inflows, wind stress, and density-induced circulation play important roles in controlling the long-term transport in the Bay. The model results shows that it requires 120–300 days for a marked change in the characteristics of the pollutant source discharged into the Bay from the Susquehanna River to affect significantly the conditions near the mouth under different hydrodynamic conditions. An increase of river discharge results in increases of downstream residual current and gravitational circulation, and thus reduces AW. The density-induced circulation contributes to the transport substantially. The dissolved substances discharged into the Bay are transported out of the Bay more rapidly when the estuary becomes more stratified. Southeasterly and southwesterly winds have strong impacts on the transport compared to the northeasterly and northwesterly winds. The former increases lateral and vertical mixing significantly. Consequently, the gravitational circulation is reduced and the transport time is increased by 50%. The model results provide useful information for understanding the long-term transport processes in the Bay.  相似文献   

Age, length and reproductive parameters of harbour porpoises Phocoena phocoena (L.) from West Greenland     

Lockyer  C.; Heide-Jorgensen  M. P.; Jensen  J.; Kinze  C. C.; Sorensen  T. Buus 《ICES Journal of Marine Science》2001,58(1):154-162

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