共查询到20条相似文献，搜索用时 31 毫秒
1.
《Dynamics of Atmospheres and Oceans》1998,28(2):107-125
Experiments are performed in a 13-m cylindrical tank to study the generation of interfacial internal waves by barotropic sinusoidal waves passing over a slope. At each tidal cycle, there are two waves generated, one propagating onshore and the other propagating offshore. The amplitude of the waves increases with increasing forcing and evolves as nonlinear waves if the shelf width is smaller than the wavelength of the baroclinic tide. Rotation does not modify the generating mechanism but the amplitude of the generated waves decreases with increasing rotation rate; also no internal waves are generated when the forcing period is larger than the inertial period, and at high rotation rate, there are only dispersive waves propagating from the shelf break region. The experiments covered a large range of internal Froude number, Rossby number and temporal Rossby number and compare well with in situ observations. 相似文献
2.
由热带气旋进入海洋近惯性运动能量的估计 总被引：2，自引：0，他引：2
根据美国联合台风警报中心(JTWC)最佳路径资料,采用Bogus方案构造了西北太平洋2000—2006年包含热带气旋的风场,作为海洋模式POM的风应力驱动,研究了西北太平洋热带气旋进入海洋近惯性运动的能量分布、传播等特征。结果表明,考虑热带气旋后西北太平洋近惯性能量增加了三倍多,约为5.14×10-3TW,其中大部分能量在低纬产生,且近半数存在于50 m以上,85%发生在海表面至水下500 m,还有15%能达到更深层次。热带气旋产生的近惯性能量在下传时,其传播方向和速度随深度呈明显差异:在上混合层,能量基本均匀,平均能在此滞留约2 d然后下传;在200 m以上,能量以垂直下传为主,下传速度非常快;在200～800m左右,能量下传路径发生右偏,下传速度较慢;在800 m以下,下传速度重新加快,并向TC路径靠近。 相似文献
3.
Atmospheric cyclones with strong winds significantly impact ocean circulation, regional sea surface temperature, and deep water formation across the global oceans. Thus they are expected to play a key role in a variety of energy transport mechanisms. Even though wind-generated internal gravity waves are thought to contribute significantly to the energy balance of the deep ocean, their excitation mechanisms are only partly understood.The present study investigates the generation of internal gravity waves during a geostrophic adjustment process in a Boussinesq model with axisymmetric geometry. The atmospheric disturbance is set by an idealized pulse of cyclonic wind stress with a Rankine vortex structure. Strength, radius and duration of the forcing are varied. The effect upon wave generation of stratification with variable mixed-layer depth is also examined.Results indicate that internal gravity waves are generated after approximately one inertial period. The outward radial energy flux is dominated by waves having structure close to vertical mode-1 and with frequency close to the inertial frequency. Less energetic higher mode waves are observed to be generated close to the sea floor underneath the storm. The total radiated energy corresponds to approximately 0.02% of the wind input. Deeper mixed-layer conditions as well as weaker stratification reduce this fraction.The low energy transfer rates suggest that other processes that drive vertical motion like surface heat fluxes, turbulent motion, mixed region collapse and storm translation are essential for significant energy extraction by internal gravity waves to occur. 相似文献
4.
The generation mechanisms of convective gravity waves in the stratosphere are investigated in a three-dimensional framework by conducting numerical simulations of four ideal storms under different environmental conditions: one un-sheared and three constant low-level sheared basic-state winds with the depth of the shear layer of 6 km and the surface wind speeds (Us) of 8, 18, and 28 m s?1, using the Advanced Regional Prediction System (ARPS) model. The storms simulated under the un-sheared (Us = 0 m s?1), weakly sheared (Us = 8 and 18ms?1), and strongly sheared (Us = 28ms?1) basicstate winds are classified into single-cell, multicell, and supercell storms, respectively. For each storm, the wave perturbations in a control simulation, including nonlinearity and microphysical processes, are compared with those in quasi-linear dry simulations forced by diabatic forcing and nonlinear forcing that are obtained from the control simulation. The gravity waves generated by the two forcing terms in the quasi-linear dry simulations are out of phase with each other for all of the storms. The gravity waves in the control simulation are represented by a linear sum of the wave perturbations generated by the nonlinear forcing and diabatic forcing. This result is consistent with the results of previous studies in a two-dimensional framework. This implies that both forcing mechanisms are important for generating the convective gravity waves in the three-dimensional framework as well. The characteristics of the three-dimensional gravity waves in the stratosphere were determined by the spectral combination of the forcing terms and the wave-filtering and resonance factor that is determined from the basic-state wind and stability as well as the vertical structure of the forcing. 相似文献
5.
The recent INSTANT measurements in the Indonesian archipelago revealed a broad spectrum of time scales that influence Indonesian Throughflow (ITF) variability, from intraseasonal (20–90 days) to interannual. The different time scales are visible in all transport and property fluxes and are the result of remote forcing by both the Pacific and Indian Ocean winds, and local forcing generated within the regional Indonesian seas. This study focuses on the time-dependent three-dimensional intraseasonal variability (ISV) in the ITF region, in particular at the locations of the INSTANT moorings at the Straits of Lombok, Ombai and Timor. Observations from the INSTANT program in combination with output from the Bluelink ocean reanalysis provide a comprehensive picture about the propagation of ISV in the ITF region. The reanalysis assimilates remotely sensed and in situ ocean observations into an ocean general circulation model to create a hindcast of ocean conditions. Data from the reanalysis and observations from the INSTANT program reveal that deep-reaching subsurface ISV in the eastern Indian Ocean and ITF is closely linked with equatorial wind stress anomalies in the central Indian Ocean. Having traveled more than 5000 km in about 14 days, the associated Kelvin waves can be detected as far east as the Banda Sea. ISV near the Straits of Ombai and Timor is also significantly influenced by local wind forcing from within the ITF region. At the INSTANT mooring sites the ocean reanalysis agrees reasonably well with the observations. Intraseasonal amplitudes are about ±1.0 °C and ±0.5 m/s for potential temperature and velocity anomalies. Associated phases of ISV are very similar in observations and the reanalysis. Where differences exist they can be traced back to likely deficits in the reanalysis, namely the lack of tidal dissipation, insufficient spatial resolution of fine-scale bathymetry in the model in narrow straits or errors in surface forcing. 相似文献
6.
利用带通滤波方法，将FSU风应力资料分离成ENSO时间尺度上的分量及其剩余部分，将这两部分分别作用于模式海洋（2层热带太平洋区域模式），研究海洋对不同时间尺度大气变化的响应。结果表明：尺管ENSO时间尺度上的风应力分量只占风应力扰动总方差的30％左右，它却能激发出全部异常风应力强迫海洋时所产生的El Nino/La Nina现象和十分相近的SSTA变化周期与振幅。而其余占总异常风应力方差60％以上的部分强迫海洋仅能产生振幅较小的海表温度异常，在非ENSO和ENSO时间尺度上的风应力强迫下，海洋中可产生相近振幅的Kelvin波，但SSTA振幅却存在显著差别，表明海洋对大气扰动信号的频率非常敏感，这里从理论上对该现象作了解释和说明。 相似文献
7.
Kenneth H. Brink 《Dynamics of Atmospheres and Oceans》1978,2(2):153-183
An attempt is made to explain the physical mechanism for the Mid-Ocean Dynamics Experiment (MODE) bottom pressure observations of Brown et al. (1975) by means of a joint laboratory and theoretical study. First, possible relevant effects in an f-plane model are considered, where pressure driving forms and transient effects can be evaluated. If atmospheric pressure change is local (of a standing wave nature), sea surface response increases with increasing subinertial frequency. If pressure changes are advective, sea surface response decreases with increasing speed. Overreaction of the free surface to forcing, causing overshoot, can occur when the free inertia-gravity modes of the basin are excited. Laboratory experiments are performed which agree with the theory of the local pressure change mechanism to within assinged experimental error.The study is extended to consider the response of an equivalent β-plane system in a more laboratory-oriented approach. It is found that the β-effect is important in the entire range of frequencies studied in the laboratory, with the response approaching that of an f-plane ocean at higher frequencies. The excitation of free planetary modes of the basin proves to be important in the barometric response, allowing for local oversoot and undershoot and for the generation of a substantial pressure signal at a distance from the driving, allowing a significant contribution to the incoherent bottom signal to be forced by distant atmospheric pressure disturbances in the ocean basin. 相似文献
8.
On the predictability of decadal changes in the North Pacific 总被引：2，自引：0，他引：2
The predictability of decadal changes in the North Pacific is investigated with an ocean general circulation model forced
by simplified and realistic atmospheric conditions. First, the model is forced by a spatially fixed wind stress anomaly pattern
characteristic for decadal North Pacific climate variations. The time evolution of the wind stress anomaly is chosen to be
sinusoidal, with a period of 20 years. In this experiment different physical processes are found to be important for the decadal
variations: baroclinic Rossby waves dominate the response. They move westward and lead to an adjustment of the subtropical
and subpolar gyre circulations in such a way that anomalous temperatures in the central North Pacific develop as a delayed
response to the preceding wind stress anomalies. This delayed response provides not only a negative feedback but also bears
the potential for long-term predictions of upper ocean temperature changes in the central North Pacific. It is shown by additional
experiments that once these Rossby waves have been excited, decadal changes of the upper ocean temperatures in the central
North Pacific evolve without any further anomalous atmospheric forcing. In the second part, the model is forced by surface
heat flux and wind stress observations for the period 1949–1993. It is shown that the same physical processes which were found
to be important in the simplified experiments also govern the evolution of the upper ocean in this more realistic simulation.
The 1976/77 cooling can be mainly attributed to anomalously strong horizontal advection due to the delayed response to persistent
wind stress curl anomalies in the early 1970s rather than local anomalous atmospheric forcing. This decadal change could have
been predicted some years in advance. The subsequent warming in the late 1980s, however, cannot be mainly explained by advection.
In this case, local anomalous atmospheric forcing needs to be considered.
Received: 6 July 1998 / Accepted: 16 October 1999 相似文献
9.
Climate variations in four millennium integrations obtained with coupled GCMs are studied from a spectral point of view.
It is shown that the bulk of these variations can be described by two distinctly different types of spectra. The type-I spectra,
characterized by a high-frequency ω−2 slope (with ω being frequency) and a low-frequency plateau, indicate the dominance of short-term fluctuations in generating
climate variations. They are obtained for many atmospheric variables and variables representing predominantly the upper ocean
and the high-latitude part of the deep ocean. The time scale, at which the spectra level off, varies from a few days for grid-point
time series of atmospheric variables, to a few months for time series of large-scale atmospheric patterns, several years for
SST anomalies in the tropical Pacific, and a few decades for variables describing oceanic baroclinic waves. The type-II spectra
are obtained in the ocean interior, which is shielded from the fluctuating forcing at the surface. Since the ocean model does
not produce oceanic eddies, the disappearance of type-I spectra in the deep ocean indicates that the fluctuating surface forcing
does not fully penetrate into the deep ocean. While type-I spectra are supported by observations, type-II spectra might describe
a model specific phenomenon and the realism of these spectra is still a open question.
Received: 12 January 2000 / Accepted: 14 June 2000 相似文献
10.
南边界强迫的非线性临界层与副高的形成、维持和振荡 总被引：4，自引：0，他引：4
用非线性准地转正压涡度方程模式，在南边界取定常强迫波，采用４种方案模拟了非线性临界层及其上激发的Ｋｅｌｖｉｎ猫眼，以确定热带的定常强迫对副高的形成、维持和振荡的影响。结果表明，南边界定常强迫仍在非线性临界层内激发行星尺度的准定常反气旋的Ｋｅｌｖｉｎ猫眼流场，猫眼的移动、强度和形状变化与夏季副高比较相似．而北边界定常强迫所得结果与夏季副高差异较大。因此，南边界所激发的非线性临界层上的Ｋｅｌｖｉｎ猫眼可能是夏季副高形成、维持和振荡的一种更为重要的新物理机制。文中还提出准定常行星波穿越副热带的非线性临界层的物理机制。 相似文献
11.
《Dynamics of Atmospheres and Oceans》2006,41(1):1-27
An analytical model is developed for the initial stage of surface wave generation at an air–water interface by a turbulent shear flow in either the air or in the water. The model treats the problem of wave growth departing from a flat interface and is relevant for small waves whose forcing is dominated by turbulent pressure fluctuations. The wave growth is predicted using the linearised and inviscid equations of motion, essentially following Phillips [Phillips, O.M., 1957. On the generation of waves by turbulent wind. J. Fluid Mech. 2, 417–445], but the pressure fluctuations that generate the waves are treated as unsteady and related to the turbulent velocity field using the rapid-distortion treatment of Durbin [Durbin, P.A., 1978. Rapid distortion theory of turbulent flows. PhD thesis, University of Cambridge]. This model, which assumes a constant mean shear rate Γ, can be viewed as the simplest representation of an oceanic or atmospheric boundary layer.For turbulent flows in the air and in the water producing pressure fluctuations of similar magnitude, the waves generated by turbulence in the water are found to be considerably steeper than those generated by turbulence in the air. For resonant waves, this is shown to be due to the shorter decorrelation time of turbulent pressure in the air (estimated as ∝ 1/Γ), because of the higher shear rate existing in the air flow, and due to the smaller length scale of the turbulence in the water. Non-resonant waves generated by turbulence in the water, although being somewhat gentler, are still steeper than resonant waves generated by turbulence in the air. Hence, it is suggested that turbulence in the water may have a more important role than previously thought in the initiation of the surface waves that are subsequently amplified by feedback instability mechanisms. 相似文献
12.
Effects of the seasonal variation in thermohaline and wind forcing on the abyssal circulation are investigated by using an
ocean general circulation model. To isolate effects of the seasonality in the thermohaline forcing from those in the wind
forcing, we carry out three experiments with (1) annual-mean wind forcing and perpetual-winter thermohaline forcing, (2) annual-mean
wind forcing and seasonal thermohaline forcing, and (3) seasonal wind forcing and seasonal thermohaline forcing. The deep
water under the seasonal thermohaline forcing becomes warmer than under the perpetual-winter thermohaline forcing. Although
the perpetual-winter thermohaline forcing is widely used and believed to reproduce the deep water better than the annual-mean
forcing, the difference between the results of the perpetual-winter and the seasonal thermohaline forcing is significant.
The seasonal variation of the Ekman convergence and divergence produces meridional overturning cells extending to the bottom
because the period of seasonal cycle is shorter than the adjustment timescale by baroclinic Rossby waves. The heat transport
owing to those Ekman flows and temperature anomalies makes the upper water (0–200 m) colder at low to mid-latitudes (40S–40N)
and warmer at high latitudes. Also the deep water becomes warmer owing to the warming of the northern North Atlantic, the
main source region of North Atlantic Deep Water. The model is also synchronously (i.e., without acceleration) integrated with
seasonal forcing for 5400 y. A past study suggested that under seasonal forcing, a sufficient equilibrium state can be achieved
after only decades of synchronous integration following more than 10 000 y of accelerated integration. Here, the result so
obtained is compared with that of the 5400-y synchronous integration. The difference in the global average temperature is
as small as 0.12 °C, and most of the difference is confined to the Southern Ocean.
Received: 1 May 1998 / Accepted: 5 January 1999 相似文献
13.
14.
《Dynamics of Atmospheres and Oceans》2002,35(2):97-130
This work is an attempt to simulate the Mediterranean Sea general circulation with a Spectral Finite Element Model. This numerical technique associates the geometrical flexibility of the finite elements for the proper coastline definition with the precision offered by spectral methods. The model is reduced gravity and we study the wind-driven ocean response in order to explain the large scale sub-basin gyres and their variability. The study period goes from January 1987 to December 1993 and two forcing data sets are used. The effect of wind variability in space and time is analyzed and the relationship between wind stress curl and ocean response is stressed. Some of the main permanent structures of the general circulation (Gulf of Lions cyclonic gyre, Rhodes gyre, Gulf of Syrte anticylone) are shown to be induced by permanent wind stress curl structures. The magnitude and spatial variability of the wind is important in determining the appearance or disappearance of some gyres (Tyrrhenian anticyclonic gyre, Balearic anticyclonic gyre, Ionian cyclonic gyre). An EOF analysis of the seasonal variability indicates that the weakening and strengthening of the Levantine basin boundary currents is a major component of the seasonal cycle in the basin.The important discovery is that seasonal and interannual variability peak at the same spatial scales in the ocean response and that the interannual variability includes the change in amplitude and phase of the seasonal cycle in the sub-basin scale gyres and boundary currents. The Coriolis term in the vorticity balance seems to be responsible for the weakening of anticyclonic structures and their total disappearance when they are close to a boundary.The process of adjustment to winds produces a train of coastally trapped gravity waves which travel around the eastern and western basins, respectively in approximately 6 months. This corresponds to a phase velocity for the wave of about 1 m/s, comparable to an average velocity of an internal Kelvin wave in the area. 相似文献
15.
Interannual variations of subsurface influence on SST in the Indian Ocean show strong seasonality. The subsurface influence on SST confines to the southern Indian Ocean (SIO) in boreal winter and spring; it is observed on both sides of the equator in boreal summer and fall. Interannual long Rossby waves are at the heart of this influence, and contribute significantly to the coupled climate variability in the tropical Indian Ocean (TIO). Principal forcing mechanism for the generation of these interannual waves in the Indian Ocean and the relative influence of two dominant interannual signals in the tropics, namely El Niño and Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD), are also discussed. Two distinct regions dominated by either of the above climate signals are identified. IOD dominates the forcing of the off-equatorial Rossby waves, north of 10°S, and the forcing comes mainly from the anomalous Ekman pumping associated with the IOD. However, after the demise of IOD activity by December, Rossby waves are dominantly forced by ENSO, particularly south of 10°S.It is found that the subsurface feedback in the northern flank of the southern Indian Ocean ridge region (north of 10°S) significantly influences the central east African rainfall in boreal fall. The Indian Ocean coupled process further holds considerable capability of predicting the east African rainfall by one season ahead. Decadal modulation of the subsurface influence is also noticed during the study period. The subsurface influence north of 10°S coherently varies with the IOD, while it varies coherently with the ENSO south of this latitude. 相似文献
16.
Decadal climate predictions with a coupled OAGCM initialized with oceanic reanalyses 总被引：2，自引：1，他引：1
A. Bellucci S. Gualdi S. Masina A. Storto E. Scoccimarro C. Cagnazzo P. Fogli E. Manzini A. Navarra 《Climate Dynamics》2013,40(5-6):1483-1497
We investigate the effects of realistic oceanic initial conditions on a set of decadal climate predictions performed with a state-of-the-art coupled ocean-atmosphere general circulation model. The decadal predictions are performed in both retrospective (hindcast) and forecast modes. Specifically, the full set of prediction experiments consists of 3-member ensembles of 30-year simulations, starting at 5-year intervals from 1960 to 2005, using historical radiative forcing conditions for the 1960–2005 period, followed by RCP4.5 scenario settings for the 2006–2035 period. The ocean initial states are provided by ocean reanalyses differing by assimilation methods and assimilated data, but obtained with the same ocean model. The use of alternative ocean reanalyses yields the required perturbation of the full three-dimensional ocean state aimed at generating the ensemble members spread. A full-value initialization technique is adopted. The predictive skill of the system appears to be driven to large extent by trends in the radiative forcing. However, after detrending, a residual skill over specific regions of the ocean emerges in the near-term. Specifically, natural fluctuations in the North Atlantic sea-surface temperature (SST) associated with large-scale multi-decadal variability modes are predictable in the 2–5 year range. This is consistent with significant predictive skill found in the Atlantic meridional overturning circulation over a similar timescale. The dependency of forecast skill on ocean initialization is analysed, revealing a strong impact of details of ocean data assimilation products on the system predictive skill. This points to the need of reducing the large uncertainties that currently affect global ocean reanalyses, in the perspective of providing reliable near-term climate predictions. 相似文献
17.
理想海域中台风引起的潮、流及波的分析 Ⅱ.海岸及陆架的影响 总被引：2，自引：0，他引：2
采用理想的大陆架地形和台风模型计算了不同方向登陆的台风所激发的海洋响应。结果表明,岸边的潮位变化主要是由于台风引起的强迫振动造成的。而对于登陆型台风来说,在远离台风路径的地方,潮位的变化则是由于边缘波效应。对地平直海岸和二维大陆架,自由边缘波的振幅远小于强迫波的振幅。平行海岸移行台风在岸边产生随台风一起移动的强制波,其中当台风沿着与Kelvin波相同的方向移行时,岸边有陆架波产生,反之则没有陆架波。此外,还讨论了与风暴潮相关的近岸环流。 相似文献
18.
We consider subinertial, free waves trapped along three coastlines (i.e., shelf waves) in an ocean governed by a geophysical model in which stratification is explicitly obtained by taking the Vaisala frequency N much greater than the inertial frequency f. The behavior is generalized in terms of the parameter S = (N/f)a where a is the bottom slope of the trapping region. Only when , are the predicted shelf waves like those predicted by Laplace's tidal equations (LTE) on an f-plane. When 0.2 ? S < 1, LTE are inappropriate because the shelf waves are only qualitatively like those predicted by LTE, and when S 1, the shelf waves are like baroclinic Kelvin waves in that they can occur at any subinertial frequency up to f (in qualitative disagreement with the predictions of LTE). Since N/f is usually a large number in the real ocean (of order 50–250), S is likely to be large unless the bottom slope is very gentle throughout the trapping region. Some applications to coastal current observations are discussed. 相似文献
19.
Geostrophic adjustment and frontogenesis are examined by means of the 2-D ARPS model.The simulation shows that.without the large-scale forcing,both the frontogenesis and frontolysisare observed during the geostrophic adjustment process and the intensity of the front oscillates inthe case of no discontinuity.The convergence (divergence) induced by the secondary circulation isthe most important factor for frontogenesis (frontolysis) at the top and bottom boundaries.Theamplitude and period of oscillation are dependent on the initial atmospheric stratification and theCoriolis frequency,and they are related to the inertio-gravity wave. 相似文献
20.
A zonal-vertical two-dimensional equatorial model is used to study the possibility that the long period oscillation of the zonal mean flow occurring in the lower equatorial stratosphere (QBO) is caused by local thermal ac-tivities at the tropical tropopause. The model successfully reproduces QBO-like oscillations of the zonal mean flow, suggesting that the local heating or cooling at the tropical tropopause is probably the main reason of QBO’s genera-tion. The analysis of the dependence of the oscillation on the wave fencing indicates that the oscillation is not sensible to the forcing scale. The model can reproduce QBO-like oscillations with any forcing scale if the fencing period and amplitude take appropriate values, proving that the internal gravity waves generated by local thermal source take much important roles in QBO. 相似文献