Continuous observation of sea water temperature and current was made at Wenchang Station(19°35′N,112°E) in 2005. The data collected indicate vigorous internal waves of both short periods and tidal and near-inertial periods. The temperature and current time series during 18-30 September were examined to describe the upper ocean internal wave field response to Typhoon Damrey(0518) . The strong wind associated with the typhoon,which passed over the sea area about 45 km south of Wenchang Station on 25 September,deepened the mixed layer depth remarkably. It decreased the mixed layer temperature while increasing the deep layer temperature,and intensified the near-inertial and high-frequency fluctuations of temperature and current. Power spectra of temperature and current time series indicate significant deviations from those obtained by using the deep ocean internal wave models characterized by a power law. The frequency spectra were dominated by three energetic bands:around the inertial frequency(7.75× 10-6 Hz) ,tidal frequencies(1.0×10-5 to 2.4×10-5 Hz) ,and between 1.4×10-4 and 8.3×10-4 Hz. Dividing the field data into three phases(before,during and after the typhoon) ,we found that the typhoon enhanced the kinetic energy in nearly all the frequency bands,especially in the surface water. The passage of Damrey made a major contribution to the horizontal kinetic energy of the total surface current variances. The vertical energy density distribution,with its peak value at the surface,was an indication that the energy injected by the strong wind into the surface current could penetrate downward to the thermocline.
WANG GangQIAO FangliHOU YijunDAI DejunLIN MinZHANG QilongWANG GangYIN Baoshu
MASNUM wave-tide-circulation coupled numerical model (MASNUM coupled model, hereinafter) is de-veloped based on the Princeton Ocean Model (POM). Both POM and MASNUM coupled model are ap-plied in the numerical simulation of the upwelling off Yangtze River estuary and in Zhejiang coastal waters in summer. The upwelling mechanisms are analyzed from the viewpoint of tide, and a new mechanism is proposed. The study suggests that the tidally inducing mechanism of the upwelling in-cludes two dynamic aspects: the barotropic and the baroclinic process. On the one hand, the residual currents induced by barotropic tides converge near the seabed, and upwelling is generated to maintain mass conservation. The climbing of the residual currents along the sea bottom slope also contributes to the upwelling. On the other hand, tidal mixing plays a very important role in inducing the upwelling in the baroclinic sea circumstances. Strong tidal mixing leads to conspicuous front in the coastal waters. The considerable horizontal density gradient across the front elicits a secondary circulation clinging to the tidal front, and the upwelling branch appears near the frontal zone. Numerical experiments are de-signed to determine the importance of tide in inducing the upwelling. The results indicate that tide is a key and dominant inducement of the upwelling. Experiments also show that coupling calculation of the four main tidal constituents (M2, S2, K1, and O1), rather than dealing with the single M2 constituent, im-proves the modeling precision of the barotropic tide-induced upwelling.
L XinGang1,2,3,4, QIAO FangLi1,2, XIA ChangShui1,2 & YUAN YeLi1,2 1 The First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China
基于普林斯顿海洋模式(POM)建立了MASNUM(Laboratory of MArine Science and NUmerical Modeling)海浪-潮流-环流耦合模式,对长江口外及浙江沿岸海域夏季的上升流现象进行了数值模拟,并从潮运动的角度分析了其动力机制,对该海域潮致上升流的形成机理给出了一种新的解释.研究表明,该海域上升流的潮生机制同时体现在正压和斜压2个方面:单纯的正压潮余流能够通过底层辐合和沿地形坡度爬升两种过程产生上升流;在斜压海洋环境下,强烈的潮混合作用在近岸陆坡区形成显著的锋面,锋面两侧存在明显的密度差异,该密度差异造成的水平压力梯度诱生出沿锋面的次级环流,其上升流分支出现在锋区附近.数值试验表明,潮运动是该海域上升流的一个极为重要的诱发因子,甚至占主导地位.研究还发现,与单纯模拟M2分潮相比,对M2,S2,K1及O14个主要分潮耦合计算有助于改善正压潮致上升流的模拟结果.
