关于海洋中的正压流和斜压流问题的讨论

关于海洋中的正压流和斜坛流的概念，目前存在着３种不同的提法．本文首先分别简述它们在定义上的差别，然后对３种定义在理解海流性质问题上的长、短处加以评述。一些理论物理海洋学家依据地转关系式，把与海面倾斜相连系的流视为正压流部分，而与密度不均匀性有关的视为斜压流部分。笔者认为这种定义在物理概念上是清楚，在实际应用中是方便，因此在讨论海流性质时最好采用这种观点。

南黄海西部夏季流的观测与分析

2006年夏季我们在南黄海西部布设并获得了1个月以上的5套ADCP锚系测流站的观测资料。本文依据所得资料分析研究了该海区的潮流分布特征,重点探讨了潮流的垂向结构,计算了潮流底Ekman层厚度。分析还表明:该海域存在较强的半日潮、近日潮、近惯性和半月频率的斜压流,其平均动能大值发生在跃层及其附近的水层中;而平均涡动动能大值出现在跃层下界以浅,最大值则在跃层上界附近。

楚科奇海夏季潮流和余流观测研究

根据2008年8月5日至9月7日在楚科奇海布放的一套锚碇潜标观测系统(71°40.024′N,167°58.910′W)获得的海流剖面资料研究了该海区的海流分布特征,重点探讨了潮流的垂向结构、余流剖面特征及海流的斜压性。结果表明:(1)该海域主要分潮为半日潮M1,S2和N2,近日分潮O1,天文分潮MM和MSF,其中以M2为代表的半日分潮最为显著,所有半日分潮的潮流椭圆均呈逆时针方向旋转;(2)整个测流剖面内平均余流呈东北偏北流向,平均余流大小为6.6cm/s;(3)各层余流存在显著的垂向同步的周期性变化;(4)在8～11m范围内平均斜压动能较强,而18m以下平均斜压动能较弱,在11～18m范围内由上而下平均斜压动能不断减弱,平均斜压余流逐渐变小。

南海文昌海域内孤立波特征观测研究

内孤立波对大陆架边缘海区的混合和生态有着显著影响,近年来已成为物理海洋学研究的热点。但是南海北部陆架的内波现场资料极为缺乏。2005年4—7月,中国科学院海洋研究所在文昌海区进行了文昌内波实验。通过此次现场观测数据发现,在4月下旬文昌海域有着强盛的内孤立波,其振幅在40m左右,产生的斜压流接近1m/s,且传播方向平行于等深线切线方向,向西南方向传播。分析还得出此类内孤立波并非发源于吕宋海峡,应该属于潮地相互作用局地生成的内孤立波。

南海北部某海洋工程海域的内潮特征研究

利用南海北部某海洋工程所在海域一套潜标系统获取的连续6个月的温盐流数据,分析研究了该海域的内潮特征,发现该海域的内潮波振幅不超过20m。在垂直方向上,中上层内潮波更明显,且主要为较强的全日内潮和较弱的半日内潮。斜压流以顺时针旋转的全日潮流为主,椭圆长轴主要呈南北走向,潮流椭圆先随深度增加而逐渐变小,在深度120~140m处达到最小,深度再往下增加又逐渐变大。同时,还发现该海域在213m以浅存在着明显的近惯性波动,其能量穿越温跃层下传。另外,在此海域还证实了东沙海流的存在,其平均流速14.3cm/s,平均流向237.6°。

Impacts of Indonesian Throughflow on seasonal circulation in the equatorial Indian Ocean

Impacts of the Indonesian Throughflow(ITF) on seasonal circulation in the equatorial eastern Indian Ocean are investigated using the ocean-only model LICOM by opening and closing ITF passages. LICOM had daily forcing from NCEP reanalysis data during 2000–2011. It can reproduce vertical profiles of mean density and buoyancy frequency of World Ocean Atlas 2013 data. The model also simulates well annual oscillation in the central Indian Ocean and semiannual oscillation in the eastern Indian Ocean of sea level anomalies(SLA) using satellite altimeter data, as well as the semiannual oscillation of surface zonal equatorial currents of Ocean Surface Current Analyses Real Time current data in the equatorial Indian Ocean. The wave decomposition method is used to analyze the propagation and reflection of equatorial long waves based on LICOM output. Wave analysis suggests that ITF blockage mainly influences waves generated from the Indian Ocean but not the Pacific Ocean, and eastern boundary reflections play an important role in semiannual oscillations of SLA and zonal current dif ferences in the equatorial Indian Ocean associated with ITF. Reconstructed ITF-caused SLA using wave decomposition coefficient dif ferences between closed and open ITF-passage experiments suggest both Kelvin and Rossby waves from the first baroclinic mode have comparable contributions to the semiannual oscillations of SLA diff erence. However, reconstructed ITFcaused surface zonal currents at the equator suggest that the first meridional-mode Rossby wave has much greater contribution than the first baroclinic mode Kelvin wave. Both reconstructed sea level and zonal currents demonstrate that the first baroclinic mode has a greater contribution than other baroclinic modes.

NUMERICAL STUDY ON THE FORMATION OF THE SOUTH CHINA SEA WARM CURRENT I. BAROTROPIC CASE

In this work, Princeton Ocean Model (POM) was used to study the formation of the South China Sea Warm Current (SCSWC) in the barotropic case. Monthly averaged wind stress and the inflow/outflow transports in January were used in the numerical simulation which reproduced the SCSWC. The effects of wind stress and inflow/outflow were studied separately. Numerical experiments showed that the Kuroshio intrusion through the Luzon Strait and the slope shelf in the northern SCS are necessary conditions for the formation of the SCSWC. In a flat bottom topography experiment, the wind stress driven northeast current in the northern SCS is a compensatory current.

Comparison of Flow Characteristics Around Refractive and Right-angled Groins in Barotropic and Baroclinic Conditions

Groins are employed to prevent nearshore areas from erosion and to control the direction of flow. However, the groin structure and its associated flow characteristics are the main causes of local erosion. In this study, we investigate the flow patterns around refractive and right-angle groins. In particular, we analytically compare the flow characteristics around a refractive groin and study the degree of accuracy that can be achieved by using a right-angle groin of various projected lengths. To compare the flow characteristics, we replaced the right-angle groin with an approximation of a refractive groin. This replacement had the least effect on the maximum velocity of flow in the channel. Moreover, we investigated the distribution of the density variables of temperature and salinity, and their effects on the flow characteristics around the right-angle groin. A comparison of the flow analysis results in baroclinic and barotropic conditions reveals that the flow characteristic values are very similar for both the refractive and right-angle groins. The geometry of the groin, i.e., right-angle or refractive, has little effect on the maximum speed to relative average speed. Apart from the angular separation, the arm length of the groin in downstream refractive groins has less effect on other flow characteristics than do upstream refractive groins. We also correlated a number of non-dimensional variables with respect to various flow characteristics and groin geometry. These comparisons indicate that the correlation between the thalweg height and width of the channel and groin arm＇s length to projection length have been approximated using linear and nonlinear formulas regardless of inner velocity in the subcritical flow.

Flow transitions in model Czochralski GaAs melt

The flow and heat transfer of molten GaAs during Czochralski growth are studied with a time-dependent and three- dimensional turbulent flow model. A transition from axisymmetric flow to nonoaxisymmetric flow and then back to axisymmetric flow again with increasing the crucible rotation rate is predicted. In the non-axisymmetric regime, the thermal wave induced by the combination of coriolis force, buoyancy and viscous force in the GaAs melt is predicted for the first time. The thermal wave is confirmed to be baroclinic thermal wave. The origin of the transition to non-axisymmetric flow is baroclinic instability. The critical parameters for the, transitions are presented, which are quantitatively in agreement with Fein and Preffer＇s experimental results, The calculated results can be taken as a reference for the growth of GaAs single-crystal of high quality,

A time-dependent baroclinic model on NEC bifurcation

As it is well-known, the North Equatorial Current (NEC) bifurcates into the Kuroshio flowing northward and the equatorward Mindanao Current, which is well depicted by Munk's theory in 1950 in terms of its climatology. However, Munk's theory is unable to tell the NEC bifurcation variability with time. In the present paper, a time-dependent baroclinic model forced by wind, in which temporal and baroclinic terms are added to Munk's equation, is proposed to examine the seasonal variability of the NEC bifurcation latitude. An analytical solution is obtained, with which the seasonal variability can be well described: NEC bifurcation reaches its northernmost position in December and its southernmost position in June with a range of about 1° in latitude, consistent with previous results with observations. The present solution will degenerate to Munk's one in the case of steady and barotropic state.

Lie Point Symmetry Algebras and Finite Transformation Groups of Baroclinic Mode for Rotating Stratified Flows

The transformation groups and symmetries of the baroclinic mode for rotating stratified flow can be obtained via the standard approach. Applying the symmetry group on some special solutions, the newly obtained results disprove a known conjecture.

Non-inverting buck-boost DC-DC converter based on constant inductor current control

The hysteresis control combined with PWM control non-inverting buck-boost was proposed to improve the light load efficiency and power density.The constant inductor current control(CICC)was established to mitigate the dependence on the external components and device variation and make smooth transition between hysteresis control loop and pulse width modulation(PWM)control loop.The small signal model was deduced for the buck and boost operation mode.The inductor current slope control(ICSC)was proposed to implement the automatic mode transition between buck and boost mode in one switching cycle.The results show that the converter prototype has good dynamic response capability,achieving 94%efficiency and 95%peak efficiency at full 10 A load current.

Second order potential vorticity and its potential applications

A new invariant, the second order potential vorticity(SPV), is derived in this paper. SPV is the dot product of vorticity and the potential vorticity(PV) gradient, and is proven conservative for a compressible, adiabatic and frictionless atmosphere. Research shows that the new invariant may be used to indicate the evolution of PV, because SPV includes all the information that determines PV evolution: the wind field, and the PV gradient. Furthermore, SPV is capable of diagnosing heavy precipitation because of the strong signals it presents in areas of heavy rainfall. SPV also shows great potential as a comprehensive conserved quantity for indicating the dynamical tropopause and baroclinic instability.

The derivation of moist baroclinic Ertel-Rossby invariant in fast manifold and its application to typhoons

Potential vorticity(PV)has been widely applied as a tracer because of its property of conservation in frictionless,dry adiabatic flow.However,PV itself is more effective in describing the slow-manifold flow at large scale.Therefore,we wish to find a materially conserved invariant other than PV to diagnose severe weather such as growing and mature tropical cyclones,whose velocity and dynamic pressure vary rapidly and locally.Starting from the absolute motion equation after elimination of the pressure gradient term by introducing moist entropy and moist enthalpy,the baroclinic Ertel-Rossby invariant(ERI)in moist flow is derived by the Weber transformation.Furthermore,the material conservation property of moist ERI is proven.Besides the traditional moist potential vorticity(MPV)term,the invariant includes the moisture factor that is excluded in dry ERI and the term related to gradients of pressure,kinetic energy and potential energy that reflects the"fast-manifold"property.Therefore,it is more complete to describe the fast motions off the slow manifold for severe weather than is the MPV term.The moist ERI is then applied to diagnose a triple-typhoon system,and is compared with MPV and dry ERI.Contrastive analysis shows that moist ERI is a better tool to diagnose the movements and intensity variations of several coexisting typhoons.The moist ERI can signify the movement and development of a multi-typhoon system.It has wide application prospects for a real moist atmosphere.

Study of Transition from Laminar to Turbulent Boundary Layer on a Tilted Flat Plate Using Heat Transfer Measurements

The boundary layer transition over a flat tilted plate has been studied by means of heat transfer measurements. A heat flux sensor has been developed, in order to measure the efficiency of convective heat transfer for various types of surfaces or flows. Its operation at constant temperature allows direct and fast measurements of heat flux. The present paper reports the development of the sensor and presents its application to the study of transition in a boundary layer depending on the angle of incidence of the external flow. An exponential relationship between critical Reynolds number and pressure gradient parameter has been found.