西沙湾工程波浪推算及波浪场数值模拟

本研究根据崇武水文站1976—2007年共31 a的波浪观测资料,使用皮尔逊Ⅲ型频率曲线进行拟合分析,推算出崇武在不同重现期条件下的特征波浪要素,再将其作为外海波浪要素输入,通过基于椭圆型缓坡方程的CGWAVE近岸波浪数值模型,模拟西沙湾的重现期波浪场,得到其设计波浪要素,得到较为合理的计算结果。西沙湾的海底地形强烈地影响近岸波浪,导致了波高和波向的不均匀分布特征,岛屿和礁石都是天然屏障,东侧水域受龟屿及闽台码头的掩护,波浪反射、绕射明显,对避风坞起到了有效的保护作用。此外,对于不同地质的边界,反射系数不同使得近岸波高分布有较大差异。     

闸坡站风暴潮增水与热带气旋登陆点及路径的关系

将1992～2006年15a间影响和登陆闸坡站的热带气旋按照登陆点和移动路径进行分类．研究各类热带气旋在闸坡站引起的风暴潮增水峰值的出现时间与热带气旋登陆点及移动路径的关系,定性分析热带气旋风场结构对风暴潮增水的影响并经过2007年至今风暴潮增水预报过程中的实例检验．结果表明：闸坡站的增水类型与热带气旋的登陆地点和路径关系密切．在闸坡站登陆的东北行热带气旋引起的风暴潮增水多出现在登陆前,其他路径则出现在登陆时或登陆后;在闸坡以西登陆的热带气旋引起的风暴潮增水峰值一般发生在登陆时或登陆后1h以内;在闸坡站以东登陆的热带气旋引起的风暴潮增水峰值一般发生在登陆前10h以上;而其他类型的热带气旋引起的风暴潮增水由于个例较少规律尚不明显．     

Topographic instability and multiple equilibria on an f-plane

Abstract

The flow of a two-layer flow in a rotating channel on an f-plane over topography with sinusoidal variation of height in a direction parallel to the flow is investigated. When the two layers flow in opposite directions a resonance is found when the topographic scale matches the free mode of the system. We examine the stability of the forced mode in the vicinity of this resonance by means of a perturbation expansion of the topographic height. Both subresonant and super-resonant instabilities are found and their equilibration is examined. For small values of the dissipation multiple equilibria are found. The topographic drag releases potential energy even when the flow is baroclinically stable.     

On the magnitude of upwelling fluxes in shelf-break canyons

A hydrodynamic model is employed to derive the magnitude of on-shelf fluxes through a shelf-break canyon for a wide range of canyon sizes and ambient oceanic conditions. Predicted canyon-upwelling fluxes are of the order of 0.05–0.1 Sv (1 Sv=1 million m³/s), being several orders of magnitude greater than upslope fluxes in the bottom Ekman layer on the ambient continental slope. On the basis of ∼150 simulations conducted, a bulk formula of upwelling flux in a submarine canyon is derived. For typical conditions, the upwelling flux varies quadratically with forcing strength (speed of incident flow), linearly with canyon depth, and is inversely proportional to the buoyancy frequency of the density stratification inside the canyon. Other parameters such as density stratification above shelf-break depth and bottom friction are found to have minor influences on the resultant canyon-upwelling flux.     

0308号强热带风暴"天鹅"影响过程分析

利用天气图、卫星云图等资料,分析了0308号强热带风暴"天鹅"的高空环流形势及演变、双热带气旋的影响、日本24小时地面预报图和降水预报图以及FY-2云图,探讨了如何预报热带气旋的移动路径、登陆地点和时段,切实提高热带气旋活动的预报准确率.     

A dynamically consistent analysis of circulation and transports in the southwestern Weddell Sea

An inverse model is applied for the analysis of hydrographic and current meter data collected on the repeat WOCE section SR4 in the Weddell Sea in 1989–1992. The section crosses the Weddell Sea cyclonic gyre from Kapp Norvegia to the northern end of the Antarctic Peninsula. The concepts of geostrophy, conservation of planetary vorticity and hydrostatics are combined with advective balances of active and passive properties to provide a dynamically consistent circulation pattern. Our variational assimilation scheme allows the calculation of three-dimensional velocities in the section plane. Current speeds are small except along the coasts where they reach up to 12 cm/s. We diagnose a gyre transport of 34 Sverdrup which is associated with a poleward heat transport of 28 × 10¹² W corresponding to an average heat flux of 15 Wm^–2 in the Weddell Sea south of the transect. This exceeds the estimated local flux on the transect of 2 Wm^–2. As the transect is located mostly in the open ocean, we conclude that the shelf areas contribute significantly to the ocean-atmosphere exchange and are consequently key areas for the contribution of the Weddell Sea to global ocean ventilation. Conversion of water masses occuring south of the section transform 6.6 ± 1.1 Sv of the inflowing warm deep water into approximately equal amounts of Weddell Sea deep water and Weddell Sea bottom water. The volume transport of surface water equals in the in-and outflow. This means that almost all newly formed surface water is involved in the deep and bottom water formation. Comparison with the results obtained by pure velocity interpolation combined with a hydrographic data subset indicates major differences in the derived salt transports and the water mass conversion of the surface water. The differences can be explained by deviations in the structure of the upper ocean currents to which shelf areas contribute significantly. Additionally a rigorous variance analysis is performed. When only hydrographic data are used for the inversion both the gyre transport and the poleward heat transport are substantially lower. They amount to less than 40% of our best estimate while the standard deviations of both quantities are 6.5 Sv and 37 × 10¹² W, respectively. With the help of long-term current meter measurements these errors can be reduced to 2 Sv and 8 × 10¹² W. Our result underlines the importance of velocity data or equivalent information that helps to estimate the absolute velocities.     

Kelvin wave generation by a semi-infinite barrier

A closed form solution is given for the problem of simple harmonic plane waves incident obliquely on a semi-infinite barrier. The amplitude of the Kelvin wave component is considered and it is found that increased amplitudes of the Kelvin waves can be expected for certain wave numbers, depending upon the angle of incidence.     

Multivariate correlation analysis of suspended-sediment characteristics

Principal component analysis (PCA) was employed to investigate interrelationships among various characteristics of seawater and suspended sediments obtained from surface waters of two Asian marginal seas. On the basis of multivariate correlation analysis for the two marginal seas combined, three important factors were extracted and interpreted: (1) current-energy conditions, (2) the influence of rivers, and (3) biochemical conditions of seawater. A relationship between anisotropic mineral grains and combustible organic matter is suggested by the fact that suspended sediment, containing coarser anisotropic mineral grains, also contains larger amounts of combustible organic matter.     

Dynamical formulation of Broecker''s model for marine cycles of biologically incorporated elements

Broecker presented a steady-state, two-box model which emphasizes the role of kinetic factors in determining the chemical composition of sea water. Unlike thermodynamic models, Broecker's model suggests that sizable temporal variation in the composition of sea water and rates of sedimentation may have taken place in the past 100 million years. To describe the evolution of the ocean's chemical system and interpret variations observed in the sedimentary record, we have formulated a dynamical model. Mass-balance consideration leads to a set of coupled nonlinear differential equations. The equations are linearized and solved for step function changes in the rate of river input and in the rate of vertical mixing. This simple model of the ocean's chemical system is shown to be stable against oscillations. Using data for the modern ocean, the response times for P, C, Si, Ca, and Ba are calculated to be of the order of 10⁴ to 10⁶ yr for changes in river and other inputs and of the order 10¹ to 10² yr for a change in the rate of vertical mixing. Analog-simulation techniques, discussed for the situation of the two-box model, provide a powerful tool for treating nonlinearities and systems with more than two components. In the final section, consequences of the dynamical formulation are compared with parameters appearing in Broecker's steady-state formulation.     

Paradigms for planktonic assemblages: 50 years of contributions from the Leigh Marine Laboratory,Northland, New Zealand

Abstract

Plankton includes the primary producers and consumers that are critical for healthy ecosystem function in the marine realm. My objective was to identify the major contributions of the Leigh Marine Laboratory to our broader understanding of planktonic assemblages. Significant contributions were made prior to 1990 on the ecology of larval fishes. From the 1990s the focus changed to the sensory biology of larval invertebrates and fishes, with a strong emphasis given to the role of reef sound in attracting potential settlers. Both early and post 1980s research has been highly influential in a paradigm shift away from passively drifting larvae that have little control over their fate. Important contributions have also been made on the dynamics of nutrient–phytoplankton interactions, larval development and aquaculture. Opportunities abound for future research on the dynamics of planktonic assemblages in shelf waters and in changing seas.