全球海洋高频波动主振荡周期的纬向带状分布特征

基于1992年10月至2000年12月的TOPEX/Poseidon和ERS-1/2卫星高度计资料,分析了周期短于150d的高频波动及其能量的空间分布特征.在功率谱密度计算基础上,分析特定频段所含能量占周期短于150d的高濒波动总能量的百分比,发现该频段最强振荡(下文称主振荡)所对应的周期从近赤道的1个月逐步增加至南北纬30°附近的4个月,进一步分析表明主振荡周期的这种变化是连续的,与西向行星Rossby波的相速随纬度增加而变慢相对应.主振荡所对应的周期在全球海洋中呈显著的带状分布.进而表明在14°N(S)附近60d周期的振荡除通常所认为的由于潮汐混淆所造成的虚假信号之外,主要是行星Rossby波形态的真实信号.     

Long baroclinic Rossby waves with periods of about 500d near 20°N in the northwest Pacific Ocean

On the basis of maps of sea level anomalies data set from October 1992 to January 2004, pronounced low frequency variations with periods of about 500 d are detected in the area near 20°N from 160°W to 130°E. A linear two-layer model is employed to explain the mechanism. It is found that the first-mode long baroclinic Rossby waves at 20°N in the northwest Pacific propagate westward in the form of free waves at a speed of about 10.3 cm/s. This confirms that the observed low frequency variabilities appear as baroclinic Rossby waves. It further shows that these low frequency variabilities around 20°N in the northwest Pacific can potentially be predicted with a lead up to 900 d.     

Long baroclinic Rossby waves with periods of about 500d near 20°N in the northwest Pacific Ocean

1IntroductionThe oceanic Rossby waves play an importantrole in the large-scale oceanic circulations.In the o-ceans baroclinic Rossby waves have surface manifes-tations of just a fewcentimeters,and wavelengths atmid-latitudes of hundreds to thousands of ki…     

Variability of the Dokdo Abyssal Current observed in the Ulleung Interplain Gap of the East/Japan Sea

Subinertial fluctuation of a strong northward deep current, which is referred to the Dokdo Abyssal Current (DAC) by Chang et al. (2009), is investigated from current records for about 16.5 and 8.0 months in the Ulleung Interplain Gap of the East/Japan Sea. The current below 300 m is bottom-intensified and has nearly depth-independent flow. Near bottom, the spectral peaks of the current were found near 10, 20, and 60 d. The DAC variability near 10 d and 20 d is reasonably consistent with the linear theory of topographic Rossby waves (TRWs) in the following aspects: (1) The motion is columnar and bottom-intensified; (2) the theoretical cutoff frequency is similar to the observation; (3) The observation-based angles of the wavenumber vector are in good agreement with the theoretical ones. The wavelengths of the TRWs with periods of near 10 d and 20 d near Dokdo are significantly shorter than those with similar timescales in the open oceans (100-250 km). It is primarily due to the weak stratification below 300 m in the East Sea. The deep current fluctuations with periods of near 10 d and 20 d were accompanied by warm events in the upper layer resulting from eddying processes and/or meandering of the Tsushima Warm Current.     

Dynamics of the Crimea shelf waters in summer

In this paper, the main results of field research into the seawater dynamics on the shelf of the Crimea in the summer of 1991 are reported. It is shown that in the weather frequency band, the oscillations with periods of 11–12 days have the greatest amplitude. These represent coastal-trapped waves with a spatial scale of the order of the length of the Black Sea coastline. These waves are generated by distant winds and significantly disturb the response of the Crimea shelf waters to local wind forcing. A transient upwelling-downwelling circulation having a period of 5–7 days is induced by local winds and is not accompanied by the generation of trapped waves at the frequency of forcing. Since the average circulation on the shelf of the Crimea is of cyclonic character, downwelling events are found more frequently and have longer time periods than the upwelling events. The wind-generated trapped waves on the shelves of the Crimea and Kerch Peninsula have an average period of 27 h. The inertial oscillations were well expressed during an experiment resembling long-wave motions.Translated by Mikhail M. Trufanov.     

Observations of Rossby waves near site D1

A theory of Rossby waves makes a number of predictions about motions below the thermocline at Site D (39°10'N, 70°W). An experiment was made to test these predictions. Kinetic energy spectra show most of the energy is associated with periods of a week to a few months. The Reynolds' stress is negative for these periods. There is high coherence and on phase shift between 1000 m and 2000 m depths. Most of the wave-number estimates point to the south-west quadrant, consistent with westward propagation and with momentum flux into the Gulf Stream and energy flux out of it. There is enough consistency between statistics based on successive 8-month records to conclude that statistics based on a single 8-month record near Site D are meaningful. In an 8-month array of twenty-six current meters, for periods of a week to a month, the divergence is small compared to the vorticity, and the motion is transverse. The energy increases toward the bottom. The observed wave-numbers and frequencies fit the theoretical dispersion relationship satisfactorily. The kinetic energy of the fluctuations is much larger near the Gulf Stream than farther upslope. The vorticity is in quadrature with the upslope velocity. I conclude there is strong evidence that topographic Rossby wave mechanics are dominant below the thermocline on the continental rise north of the Gulf Stream.     

Interaction between a synoptic eddy and a Rossby wave

The behaviour of an isolated synoptic eddy on the -plane in the field of a plane Rossby wave is reported. As is shown, the eddy exchanges its energy intensively with Rossby waves having zero frequency in the frame of axes moving with the eddy. If the Rossby wave has an amplitude exceeding some critical value, a transition from average translational eddy motion along the meridian to oscillations in the vicinity of the equilibrium latitude is possible.Translated by Mikhail M. Trufanov. UDK 551.465.535:551.466.     

Analysis of thermohaline and current distribution characteristics of Zhejiang and Fujian waters in summer

This paper analyzed the distribution of thermohaline and circulation characteristics of Zhejiang and Fujian waters, based on the cross-sectional thermohaline data and on current data (up to 30 d duration) at fixed-point moorings, collected in the summer of 2006. We also performed low-pass filtering and spectrum analysis on the mooring submersible buoy data. Based on that analysis, we discussed the characteristics of low frequency currents and time-variations in these waters. The main conclusions are as follows. (1) There is a low salinity pinnate area near the Hangzhou Bay in summer, and outside the low salinity area, an obvious salinity front is present from surface to bottom near 123°E. There is also a temperature front below the surface at a corresponding position. (2) Bottom water of the Taiwan Warm Current comes from the subsurface of Kuroshio. (3) The direction of low frequency current at fixed anchor stations is N-NE or S, which mainly depends on the interaction of control currents in this waters. (4) Significant spectral peaks at all mooring stations are typically semidiurnal and diurnal tides. Semidiurnal tidal waves are the main ones in these waters, and have more energy closer to the shore. (5) Significant energy spectral peaks of middle period (3 to 8 d) of currents are responses to weather frequency. (6) Significant energy spectral peaks of long periods at the surface or bottom are probably responses to seasonal wind or bottom friction, while, the long period peaks of other depths can reflect cyclical changes of interactions between currents. We conclude that the pulsation period of the Taiwan Warm Current in these waters is 10-17 d.     

粤东后江湾冲流带滩面高频振动及动力作用分析

利用涌浪影响下短时段内的冲流带滩面高频高程数据和碎波带波流资料,在奇异谱分析(SSA)的基础上,对比研究了不同形态滩面的冲淤变化趋势、趋势分布形状、冲淤变化周期和冲淤变化强度,以及同一条剖面不同桩点间各因素间的变化关系;用交叉谱方法探索了每分钟滩面高频冲淤变化与碎波带长重力波间的作用关系。分析结果表明,滩角韵律地形引起的冲流分流作用促进了滩脊向滩谷的泥沙转运,冲流带滩面存在明显的长重力波频段的周期性冲淤振动,滩面冲淤振动强度由滩面下部向上部递减,碎波带长重力波对滩面高频冲淤变化起重要作用。     

Long-period waves in the vicinity of Onagawa Bay (I)

To investigate the response characteristics of a bay to tsunamis, field measurements of long-period waves have been carried out at Onagawa and Okachi Bays, both of which face the Pacific Ocean in northern Japan. In Onagawa Bay, the observed transfer function is in good agreement with the prediction based on the one-dimensional numerical model, in the period range larger than about 15 minutes. The response of shorter periods seems to be influenced by the two-dimensionality of the bay. The oscillations within Onagawa Harbor are also discussed with respect to the relative amplitude and phase at two stations inside the harbor and it is estimated that the reflection coefficient at the waterfront is about 0.7. In Okachi Bay, the oscillations in the period range larger than about 10 minutes could be explained by a Y-shaped model of the bay. The dominant oscillations offshore of these two-bays are found to be the mode with the motion predominantly in the direction normal to the shelf orientation, and the estimated power spectral density of incoming waves in deep water varies asf ^–2,f being the frequency. The waves of lateral modes, such as edge waves on the shelf, are small and of minor importance to generate bay oscillations of longer periods.     

Generation of a double Kelvin wave resulting from the reflection of the Rossby wave by the jump layer

This paper considers the evolution of a spatially-localized divergent Rossby wave field near the depth jump. If the jump magnitude is comparable to the depth, Rossby waves are fully reflected and a double Kelvin wave is then generated. The Rossby waves and the double Kelvin wave are described by the first- and zero-approximation fields of the asymptotic expansion, respectively. Over the characteristic Rossby wave period, the level elevation produced by the double Kelvin wave spreads over an extensive area, theraby making up for the change in the total fluid mass of the Rossby waves.Translated by Vladimir A. Puchkin.     

有界赤道大洋波包解及其年际年代际变率

Linearized shallow water perturbation equations with approximation in an equatorial β plane are used to obtain the analytical solution of wave packet anomalies in the upper bounded equatorial ocean. The main results are as follows. The wave packet is a superposition of eastward travelling Kelvin waves and westward travelling Rossby waves with the slowest speed, and satisfies the boundary conditions of eastern and western coasts, respectively.The decay coefficient of this solution to the north and south sides of the equator is inversely proportional only to the phase velocity of Kelvin waves in the upper water. The oscillation frequency of the wave packet, which is also the natural frequency of the ocean, is proportional to its mode number and the phase velocity of Kelvin waves and is inversely proportional to the length of the equatorial ocean in the east-west direction. The flow anomalies of the wave packet of Mode 1 most of the time appear as zonal flows with the same direction. They reach the maximum at the center of the equatorial ocean and decay rapidly away from the equator, manifested as equatorially trapped waves. The flow anomalies of the wave packet of Mode 2 appear as the zonal flows with the same direction most of the time in half of the ocean, and are always 0 at the center of the entire ocean which indicates stagnation, while decaying away from the equator with the same speed as that of Mode 1. The spatial structure and oscillation period of the wave packet solution of Mode 1 and Mode 2 are consistent with the changing periods of the surface spatial field and time coefficient of the first and second modes of complex empirical orthogonal function(EOF)analysis of flow anomalies in the actual equatorial ocean. This indicates that the solution does exist in the real ocean, and that El Ni?o-Southern Oscillation(ENSO) and Indian Ocean dipole(IOD) are both related to Mode 2.After considering the Indonesian throughflow, we can obtain the length of bounded equatorial ocean by taking the sum of that of the tropical Indian Ocean and the tropical Pacific Ocean, thus this wave packet can also explain the decadal variability(about 20 a) of the equatorial Pacific and Indian Oceans.     

Transmission and reflection of the Rossby waves in a stratified ocean with bottom topography

Transmission and reflection coefficients are calculated for Rossby waves incident on a bottom topography with constant slope in a continuously stratified ocean. The characteristics of the coefficients are interpreted in terms of the quasigeostrophic waves on the slope. In the parameter range where only the barotropic Rossby waves can propagate in the region outside the slope, the bottom trapped wave plays the same role as the topographic Rossby wave in a homogeneous ocean, and hence the transmission is weak unless phase matching takes place. When both of the barotropic and baroclinic Rossby waves can propagate outside the slope, the total transmission can be strong. The bottom trapped wave affects the transmission and reflection, and it leads to the possibility that the Rossby wave is transmitted as a mode different from the incident mode. When the number of the wavy modes on the slope is smaller than that of the Rossby wave modes outside the slope, strong reflection occurs.The results for an ocean with linear distribution of the squared Brunt-Väisälä frequency are compared to those in a uniformly stratified ocean. The weakening of the stratification near the bottom is almost equivalent to reducing the effect of the slope.     

南海北部台风和中尺度暖涡对近惯性振荡的影响

基于2014年8-9月南海北部东沙群岛附近海域两个临近站位(站位A,20.736°N,117.745°E,水深1 249 m;站位B,20.835°N,117.56°E,水深848 m)的潜标数据,研究了台风过境所激发的近惯性振荡的特征,分析了中尺度暖涡对近惯性频率的调制及其对近惯性动能分布和传播的影响。站位A(B)142(175) m以浅,近惯性频率由0.710 1(0.713 3)周/d红移至0.659 2周/d,频率减小了7.2%(7.6%),观测结果与两个站位所处的背景涡度相吻合。中尺度暖涡改变了水体层结状态,两个站位的近惯性动能在不同层结中被改变了0.5~3倍。水体层结对能量的折射作用使得站位B的近惯性动能在深度158~223 m之间衰减较少,而站位A的近惯性动能则随着深度的增加快速减小。站位A和站位B近惯性内波的垂向群速度分别约为15.2 m/d和14.1 m/d。如果忽略近惯性动能的水平辐散,近惯性内波的垂向传播分别造成了两个站位垂向上约47%和38%的近惯性动能衰减。     

Equatorially trapped Rossby waves in the presence of meridionally sheared baroclinic flow in the Pacific Ocean

TOPEX/POSEIDON altimeter data are analyzed for the 8.5-year period November 1992 to May 2001 to investigate the sea surface height (SSH) and geostrophic velocity signatures of quasi-annual equatorially trapped Rossby waves in the Pacific. The latitudinal structures of SSH and both components of geostrophic velocity are found to be asymmetric about the equator across the entire Pacific with larger amplitude north of the equator. The westward phase speeds are estimated by several different methods to be in the range 0.5-0.6 m s⁻¹. These observed characteristics are inconsistent with the classical theory for first vertical, first meridional mode equatorially trapped Rossby waves, which predicts a phase speed of about 0.9 m s⁻¹ with latitudinally symmetric structures of SSH and zonal velocity and antisymmetric structure of meridional velocity. The observations are even less consistent with the latitudinal structures of SSH and geostrophic velocity components for other modes of the classical theory.The latitudinal asymmetries deduced here have also been consistently observed in past analyses of subsurface thermal data and altimeter data and have been variously attributed to sampling errors in the observational data, a superposition of multiple meridional Rossby wave modes, asymmetric forcing by the wind, and forcing by cross-equatorial southerly winds in the eastern Pacific. We propose a different mechanism to account for the observed asymmetric latitudinal structure of low-frequency equatorial Rossby waves. From the free-wave solutions of a simple 1.5-layer model, it is shown that meridional shears in the mean equatorial current system significantly alter the potential vorticity gradient in the central and eastern tropical Pacific. The observed asymmetric structures of sea surface height and geostrophic velocity components are found to be a natural consequence of the shear modification of the potential vorticity gradient. The mean currents also reduce the predicted westward phase speed of first meridional mode Rossby waves, improving consistency with the observations.     

浙江近海波浪能资源的初步研究

以2000年为例,采用SWAN波浪数值模型对浙江近海海域的波浪进行了全年模拟计算,并计算获得年、月平均波功率密度分布。研究表明,浙江近岸海域年平均波功率密度约为2~6 kW·m^-1,往外海逐渐增大;同时季节变化明显,秋、冬季节波功率密度较大,春、夏季节较小。另外,通过对浙北、浙中和浙南3个近海海区的波浪出现频率和波功率密度随波高和周期变化的分析可知,浙北海域波功率密度比较高的波高及周期范围和波浪出现频率较高范围较为接近,而其对应平均波功率密度相对较低;浙南海域波功率密度比较高的范围所对应的平均波功率密度较高,而与波浪出现频率较高的范围则略有差异;浙中海域居两者之间。总体而言,浙江近海波浪能资源丰富,且全年中可开发与利用的波浪能出现频率较高。     

Spectral characteristics of Rossby waves in the Northwestern Pacific based on satellite altimetry

Using satellite altimetry measurement data for 1993–2013, we study the spectral characteristics of Rossby waves in the Northwestern Pacific (25°–50° N, 140°–180° E). For each latitude degree, we draw integral plots of spectral power density calculated with a two-dimensional Fourier transform (2D-FFT). We compare the dispersion equations of Rossby waves calculated from the WKB-approximation and an approximation of a two-layer ocean model with the empirical velocities determined by the slope of isopleths by the Radon method; also, we compare the dispersion equations with the spectral distributions of level variations. It is shown that the main energy of Rossby waves in the Northwestern Pacific corresponds to the first baroclinic mode. At almost all latitudes, there is good agreement between the empirical phase velocities calculated by isopleths by the Radon method and the theoretical values; also, the spectral peaks correspond to graphs of the dispersion equations for the first baroclinic mode Rossby waves, except for the Kuroshio region, where some peaks correspond to the second mode.     

大风影响下的莱州湾西岸单站底层泥沙输运特征分析

基于2018年10月21日至11月6日莱州湾西岸连续站观测数据,本文利用集合经验模态分解、希尔伯特?黄变换和小波分析法对底层单宽输沙率的小尺度特征做分析,并针对观测期间出现的大风天气对泥沙输运的影响进行了探究。结果表明,单宽输沙率在观测时间段内具有高频、潮周期、低频以及长周期尺度变化特征,周期尺度从小到大。其中高频和潮周期分量方差贡献率及所含能量最高,对输沙率的影响最强。边际谱显示东西方向输沙率的显著周期为13.3 h,南北方向大于11 h的周期较为显著。观测期间底层净泥沙通量分别为东向305.77 kg/m、南向597.25 kg/m,余流分量贡献最大,低频和高频分量贡献最小。上强迫风场主要在风速衰减期通过湍流和波浪影响输沙速率的时频分布,使其低频变化显著增强的同时,产生1 h周期左右的高频波动。交叉小波分析显示,风速和单宽输沙率在低频波段上相干性较强,且单宽输沙率会滞后风速1/4至1/2个周期。另外,风浪会增强泥沙输运的涨落潮不对称性,进而增加潮周期分量上的泥沙净输运。     

Intraseasonal variability of the surface zonal current in the equatorial Indian Ocean: Seasonal differences and causes

Using observations and numerical simulations, this study examines the intraseasonal variability of the surface zonal current(u ISV) over the equatorial Indian Ocean, highlighting the seasonal and spatial differences, and the causes of the differences. Large-amplitude u ISV occurs in the eastern basin at around 80°–90°E and near the western boundary at 45°–55°E. In the eastern basin, the u ISV is mainly caused by the atmospheric intraseasonal oscillations(ISOs), which explains 91% of the standard...     

Is asymptotic non-divergence of the large-scale tropical atmosphere consistent with equatorial wave theories?

Observations suggest that the large-scale tropical atmospheric circulations, associated with intraseasonal variabilties, are dominated more by the vorticity than the divergence. The present paper examines the consistency of the above observations with linear equatorial wave theories. Both free and forced linear waves are considered. The free equatorial waves are classified into two major categories: (1) the Rossby waves, strongly dominated by vorticity and (2) the inertial-gravity waves, relatively dominated by the divergence. Both the Kelvin and the mixed-Rossby gravity waves are intermediate of these two major categories.
In the forced case, the wave response is predominantly inertial-gravity wave-like for periods less than 5 d, thus predominantly divergent. On the other hand, for forcing with the longer periods, the wave response closely following free Rossby-wave structures, asymptotically approaches to a non-divergent state. The asymptotic tendency for non-divergence is found to be much stronger than observed. The difference is so stark that, notably, the tropical intraseasonal variability cannot be consistent with linear equatorial waves theories.