首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 500 毫秒
1.
A baroclinic shallow-water model is developed to investigate the effect of the orientation of the eastern ocean boundary on the behavior of equatorial Kelvin waves. The model is formulated in a spherical polar coordinate system and includes dissipation and non-linear terms, effects which have not been previously included in analytical approaches to the problem. Both equatorial and middle latitude response are considered given the large latitudinal extent used in the model. Baroclinic equatorial Kelvin waves of intraseasonal, seasonal and annual periods are introduced into the domain as pulses of finite width. Their subsequent reflection, transmission and dissipation are investigated. It is found that dissipation is very important for the transmission of wave energy along the boundary and for reflections from the boundary. The dissipation was found to be dependent not only on the presence of the coastal Kelvin waves in the domain, but also on the period of these coastal waves. In particular the dissipation increases with wave period. It is also shown that the equatorial β-plane approximation can allow an anomalous generation of Rossby waves at higher latitudes. Nonlinearities generally have a small effect on the solutions, within the confines of this model.  相似文献   

2.
A numerical model for the global tsunamis computation constructed by Kowalik et al. (2005), is applied to the tsunami of 26 December, 2004 in the World Ocean from 80°S to 69°N with spatial resolution of one minute. Because the computational domain includes close to 200 million grid points, a parallel version of the code was developed and run on a Cray X1 supercomputer. An energy flux function is used to investigate energy transfer from the tsunami source to the Atlantic and Pacific Oceans. Although the first energy input into the Pacific Ocean was the primary (direct) wave, reflections from the Sri Lankan and eastern shores of Maldives were a larger source. The tsunami traveled from Indonesia, around New Zealand, and into the Pacific Ocean by various routes. The direct path through the deep ocean to North America carried miniscule energy, while the stronger signal traveled a considerably longer distance via South Pacific ridges as these bathymetric features amplified the energy flux vectors. Travel times for these amplified energy fluxes are much longer than the arrival of the first wave. These large fluxes are organized in the wave-like form when propagating between Australia and Antarctica. The sources for the larger fluxes are multiple reflections from the Seychelles, Maldives and a slower direct signal from the Bay of Bengal. The energy flux into the Atlantic Ocean shows a different pattern since the energy is pumped into this domain through the directional properties of the source function. The energy flow into the Pacific Ocean is approximately 75% of the total flow to the Atlantic Ocean. In many locations along the Pacific and Atlantic coasts, the first arriving signal, or forerunner, has lower amplitude than the main signal which often is much delayed. Understanding this temporal distribution is important for an application to tsunami warning and prediction.  相似文献   

3.
A mesoscale non-hydrostatic atmospheric model has been coupled with a mesoscale oceanic model. The case study is a four-day simulation of a strong storm event observed during the SEMAPHORE experiment over a 500 × 500 km2 domain. This domain encompasses a thermohaline front associated with the Azores current. In order to analyze the effect of mesoscale coupling, three simulations are compared: the first one with the atmospheric model forced by realistic sea surface temperature analyses; the second one with the ocean model forced by atmospheric fields, derived from weather forecast re-analyses; the third one with the models being coupled. For these three simulations the surface fluxes were computed with the same bulk parametrization. All three simulations succeed well in representing the main oceanic or atmospheric features observed during the storm. Comparison of surface fields with in situ observations reveals that the winds of the fine mesh atmospheric model are more realistic than those of the weather forecast re-analyses. The low-level winds simulated with the atmospheric model in the forced and coupled simulations are appreciably stronger than the re-analyzed winds. They also generate stronger fluxes. The coupled simulation has the strongest surface heat fluxes: the difference in the net heat budget with the oceanic forced simulation reaches on average 50 Wm−2 over the simulation period. Sea surface-temperature cooling is too weak in both simulations, but is improved in the coupled run and matches better the cooling observed with drifters. The spatial distributions of sea surface-temperature cooling and surface fluxes are strongly inhomogeneous over the simulation domain. The amplitude of the flux variation is maximum in the coupled run. Moreover the weak correlation between the cooling and heat flux patterns indicates that the surface fluxes are not responsible for the whole cooling and suggests that the response of the ocean mixed layer to the atmosphere is highly non-local and enhanced in the coupled simulation.  相似文献   

4.
I report the discovery of a low frequency temperature oscillation in the eastern North Atlantic (NA), which was significantly correlated with the Southern Oscillation Index (SOI) in the tropical Pacific, but led the latter index by a number of months. This discovery is significant, because it demonstrates a link between the tropical Pacific and the high northerly latitudes which cannot readily be explained in terms of El Niño/Southern Oscillation (ENSO) feedbacks from the tropics, and opens up the possibility that ENSO and temperature anomalies in northerly climes, may actually have a common origin within, or even external to, the global climate system.  相似文献   

5.
基于祁连山地区78个地震台站的垂直分量连续波形记录,计算台站对之间背景噪声的互相关函数,并叠加得到5-10 s和10-20 s两个周期的瑞利面波信号。利用归一化振幅方法,分析不同周期范围的噪声源能量在不同方位随季节变化的规律。研究结果显示：祁连山地区5-10 s周期背景噪声的能量优势来源,夏季集中在110°-170°方位,冬季集中在300°-350°方位,但在110°-150°方位也有相对微弱的能量分布,表明第二微震带的噪声能量来源在夏季主要来源于太平洋的海洋活动,冬季主要来源于大西洋的海洋活动;10-20 s周期背景噪声的能量优势来源在夏季集中在70°-150°和170°-230°方位,在冬季则集中在290°-350°和70°-130°方位,表明第一微震带的噪声能量在夏季主要来源于印度洋的海洋区域,冬季主要来源于北大西洋和太平洋。由于2个周期的背景噪声源在祁连山地区存在明显的季节差异,因此在利用背景噪声方法研究该地区介质速度结构时,需充分考虑噪声源非均匀性产生的影响。  相似文献   

6.
The sensitivity of the bifurcation of the North Equatorial Current in the Pacific to different wind products is investigated. Variations of the bifurcation latitude with season is simulated in a purely wind-driven model and is found to be in agreement with recent observations. The seasonal cycle is nearly independent of the wind climatology, but the annual average latitude depends on the wind stress curl. It is also shown that in the upper ocean, the poleward shift in bifurcation latitude with depth is realistic in our simple model. This implies that given a stratification close to the observed, it is primarily the wind forcing that determines the location of the bifurcation and its seasonal variation.  相似文献   

7.
The interaction of warm core rings with a western wall and shelf/slope is examined with a three-dimensional primitive-equation model. The model ring is initialized with an axisymmetric Gaussian-type anticyclonic eddy placing far from the coastal boundary to allow the ring to freely propagate towards the wall and shelf/slope. The ring initially propagates steadily to the southwest at about 3 km/day under the combined planetary β and nonlinear effects. When colliding with a wall, the ring adjusts into a ‘D’ shape and moves poleward under primarily the image effect. When colliding with a shelf and slope, the ring however becomes stalled and bounces on and off the shelf/slope with little net movement. Small cyclones marked by strong upwelling are generated near the shelfbreak. Cyclones and anticyclones also are spawned at the periphery of the ring. Satellite SST images and concurrent ADCP transects are used to illustrate the strong interaction of a Gulf Stream warm ring (99B) with the Middle Atlantic Bight.  相似文献   

8.
Averaged seasonal variations of wind perturbation intensities and vertical flux of horizontal momentum produced by internal gravity waves (IGWs) with periods 0.2/1 h and 1/6 h are studied at the altitudes 65/80 km using the MU radar measurement data from the middle and upper atmosphere during 1986/1997 at Shigaraki, Japan (35°N, 136°E). IGW intensity has maxima in winter and summer, winter values having substantial interannual variations. Mean wave momentum flux is directed to the west in winter and to the east in summer, opposite to the mean wind in the middle atmosphere. Major IGW momentum fluxes come to the mesosphere over Shigaraki from the Pacific direction in winter and continental Asia in summer.  相似文献   

9.
One of the main challenges of the Copernicus Marine Service is the implementation of coupled ocean/waves systems that accurately estimate the momentum and energy fluxes provided by the atmosphere to the ocean. This study aims to investigate the impact of forcing the Nucleus for European Modelling of the Ocean (NEMO) ocean model with forecasts from the wave model of Météo-France (MFWAM) to improve classical air-sea flux parametrizations, these latter being mostly driven by the 10-m wind. Three wave-related processes, namely, wave-state-dependent stress, Stokes drift-related effects (Stokes-Coriolis force, Stokes drift advection on tracers and on mass), and wave-state-dependent surface turbulence, are examined at a global scale with a horizontal resolution of 0.25°. Three years of sensitivity simulations (2014–2016) show positive feedback on sea surface temperature (SST) and currents when the wave model is used. A significant reduction in SST bias is observed in the tropical Atlantic Ocean. This is mainly due to the more realistic momentum flux provided by the wave model. In mid-latitudes, the most interesting impact occurs during the summer stratification, when the wind is low and the wave model produces a reduction in the turbulence linked with wave breaking. Magnitudes of the large-scale currents in the equatorial region are also improved by 10% compared to observations. In general, it is shown that using the wave model reduces on average the momentum and energy fluxes to the ocean in tropical regions, but increases them in mid-latitudes. These differences are in the order of 10 to 20% compared with the classical parametrizations found in stand-alone ocean models.  相似文献   

10.
The Northeast Atlantic possesses some of the highest wave energy levels in the world. The recent years have witnessed a renewed interest in harnessing this vast energy potential. Due to the complicated geomorphology of the Irish coast, there can be a significant variation in both the wave and wind climate. Long-term hindcasts with high spatial resolution, properly calibrated against available measurements, provide vital information for future deployments of ocean renewable energy installations. These can aid in the selection of adequate locations for potential deployment and for the planning and design of those marine operations. A 34-year (from 1979 to 2012), high-resolution wave hindcast was performed for Ireland including both the Atlantic and Irish Sea coasts, with a particular focus on the wave energy resource. The wave climate was estimated using the third-generation spectral wave model WAVEWATCH III®; version 4.11, the unstructured grid formulation. The wave model was forced with directional wave spectral data and 10-m winds from the European Centre for Medium Range Weather Forecasts (ECMWF) ERA-Interim reanalysis, which is available from 1979 to the present. The model was validated against available observed satellite altimeter and buoy data, particularly in the nearshore, and was found to be excellent. A strong spatial and seasonal variability was found for both significant wave heights, and the wave energy flux, particularly on the north and west coasts. A strong correlation between the North Atlantic Oscillation (NAO) teleconnection pattern and wave heights, wave periods, and peak direction in winter and also, to a lesser extent, in spring was identified.  相似文献   

11.
Observations of the horizontal wind field over the South Pole were made during 1995 using a meteor radar. These data have revealed the presence of a rich spectrum of waves over the South Pole with a distinct annual occurrence. Included in this spectrum are long-period waves, whose periods are greater than one solar day, which are propagating eastward. These waves exhibit a distinct seasonal occurrence where the envelope of wave periods decreases from a period of 10 days near the fall equinox to a minimum of 2 days near the winter solstice and then progresses towards a period near 10 days at the spring equinox. Computation of the meridional gradient of quasi-geostrophic potential vorticity has revealed a region in the high-latitude upper mesosphere which could support an instability and serve as a source for these waves. Estimation of the wave periods which would be generated from an instability in this region closely resembles the observed seasonal variation in wave periods over the South Pole. These results are consistent with the hypothesis that the observed eastward propagating long-period waves over the South Pole are generated by an instability in the polar upper mesosphere. However, given our limited data set we cannot rule out a stratospheric source. Embedded in this spectrum of eastward propagating waves during the austral winter are a number of distinct wave events. Eight such wave events have been identified and localized using a constant-Q filter bank. The periods of these wave events ranges from 1.7 to 9.8 days and all exist for at least 3 wave periods. Least squares analysis has revealed that a number of these events are inconsistent with a wave propagating zonally around the geographic pole and could be related to waves propagating around a dynamical pole which is offset from the geographic pole. Additionally, one event which was observed appears to be a standing oscillation.  相似文献   

12.
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.  相似文献   

13.
Summary By means of highly truncated spherical harmonic expansions, an extended four-level quasi-geostrophic model with variable Coriolis parameter is transformed into a set of ordinary non-linear differential equations. Non-adiabatic effects, frictional dissipation, and boundary effects are approximately included in the equations. A numerical experiment made with the equations succeeds in producing many realistic statistical gross features, especially in the lower stratosphere, e. g., a poleward temperature incrase, the up-gradient horizontal transports of heat and momentum due to large-scale eddies, the upward energy flux of extra-long waves, and the trapping of the upward energy flux of tropospheric unstable waves near the tropopause. The mean energy flow in the lower stratosphere and in the troposphere are analyzed and compared with each other, indicating very clearly the baroclinical activness of the troposphere and the passiveness of the lower stratosphere. The dynamics in the lower stratosphere are discussed. the mean meridional circulation is also studied.  相似文献   

14.
广东及其邻域噪声面波层析成像   总被引：1，自引：1，他引：0       下载免费PDF全文
沈玉松  康英 《地震学报》2014,36(5):826-836
通过收集广东及其邻域104个固定地震台站近10个月的垂直分量连续波形数据资料, 使用地震背景噪声互相关格林函数方法, 获得了大部分台站对的背景噪声互相关曲线. 基于这些对称叠加的互相关曲线, 利用时频分析方法, 进一步提取了该地区周期为5—40 s的基阶瑞雷波群速度频散曲线. 其噪声来源分析结果显示: 广东及其邻域的噪声场来源有很强的方向性, 短周期(5—10 s)噪声主要来自东南方向, 范围基本与海岸线分布一致, 可能是由于近海水陆相互作用产生的;较长周期 (15—30 s) 噪声主要来自三大洋的方位. 以这些提取的噪声面波资料为基础, 采用噪声面波层析成像方法反演得到了该地区周期为5—28 s的瑞雷波群速度层析成像图, 从该图可以看出, 广东及其邻域地下结构的横向变化总体较小, 沉积层厚度较薄, 地壳中可能普遍存在一个低速层;从研究区历史地震的分布及其表层地质构造的发育特征来看, 地震主要分布在高、低速过渡带附近, 表明面波群速度与地震之间具有较强的耦合关系;从群速度的低速异常特征来看, 广东及其邻域普遍分布的温泉和高地热主要受深部构造的控制和影响.   相似文献   

15.
A three-level, -plane, filtered model is used to simulate the Northern Hemisphere summer monsoon. A time-averaged initial state, devoid of sub-planetary scale waves, is integrated through 30 days on a 5° latitude-longitude grid. Day 25 through day 30 integrations are then repeated on a 2.5° grid. The planetary-scale waves are forced by time-independent, spatially varying diabatic heating. Energy is extracted via internal and surface frictional processes. Orography is excluded to simplify synoptic-scale energy sources.During integration the model energy first increases, but stabilizes near day 10. Subsequent flow patterns closely resemble the hemisphere summer monsoon. Climatological features remain quasi-stationary. At 200 mb high pressure dominates the land area, large-scale troughs are found over the Atlantic and Pacific Oceans, the easterly jet forms south of Asia, and subtropical jets develop in the westerlies. At 800 mb subtropical highs dominate the oceans and the monsoon trough develops over the Asian land mass. The planetary scales at all levels develop a realistic cellular structure from the passage of transient synoptic-scale features, e.g., a baroclinic cyclone track develops near 55°N and westward propagating waves form in the easterlies.Barotropic redistribution of kinetic energy is examined over a low-latitude zonal strip using a Fourier wave-space. In contrast to higher latitudes where the zonal flow and both longer and shorter waves are fed by barotropic energy redistribution from the baroclinically unstable wavelengths, the low-latitude waves have a planetary-scale kinetic energy source. Wave numbers 1 and 2 maintain both the zonal flow and all shorter scales via barotropic transfers. Transient and standing wave processes are examined individually and in combination.Wave energy accumulates at wave numbers 7 and 8 at 200 mb and at wave number 11 in the lower troposphere. The 800-mb waves are thermally indirect and in the mean they give energy to the zonal flow. These characteristics agree with atmospheric observation. The energy source for these waves is the three wave barotropic transfer. The implications of examining barotropic processes in a Fourier wave-space, vice the more common approach of separating the flow into a mean plus a deviation are discussed.  相似文献   

16.
The equatorial undercurrent (EUC), the shallow meridional overturning cells feeding it, and their role in El Niño and decadal variability in the equatorial Pacific are studied using both in situ data and an ocean general circulation model. Using temperature and current data from the TAO/TRITON moorings at the equator, their data gaps are filled and it was shown that continuous time series of mass transport, temperature, depth, and kinetic energy of the EUC could be constructed for the period 1980–2002 with an excellent accuracy. This dataset was analysed and used to validate the output from an oceanic general circulation model (OGCM). The OGCM was then used to find that variations in the strength of the EUC, shallow meridional overturning (pycnocline convergence and surface divergence), and equatorial upwelling had the same variations in mass transport on interannual and longer time scales within the period 1951–1999. These variations are all caused by variations of the zonal wind stress zonally integrated, in agreement with simple linear and steady dynamics theories. Impact of these mass transport variations and of temperature variations on heat budgets in the entire equatorial band of the Pacific and in its eastern part are quantified.  相似文献   

17.
EISCAT radar experiments over a full solar cycle between January 1984 and March 1995 have been used to construct meridional neutral wind patterns in the ionospheric F region. For locally geomagnetically quiet periods the neutral winds have been binned according to season, solar activity, and universal time. The diurnal and seasonal behaviors and the effect of the solar flux are described. An empirical model of the meridional neutral wind for the high latitudes at eight altitudes in the ionospheric F region over a full solar cycle is presented. Results are compared with other recent empirical models.  相似文献   

18.
Regional characteristics of the synoptic-scale wave disturbances in the tropical lower troposphere were examined by analyzing the FGGE level III-b data. Three tropical regions, western Pacific, eastern Pacific, and a region from the African Continent to the Atlantic, were selected for the present study. Spectrum analysis, trajectory analysis and composite analysis were used to obtain characteristics of the wave disturbances for each region.Main findings are as follows: 1.) The generation region of the western Pacific wave disturbances related to typhoon development are found around 5° N and 170° E. 2.) An interaction of the western Pacific wave disturbances with the upper Mid-Pacific trough was indicated statistically as an intensifying condition for typhoons. 3.) The wave disturbances in the eastern Pacific originate to the west of Panama and propagate west-north-westward with a period of 5.7 day and a wavelength of about 2700 km. 4.) The structure of the eastern Pacific wave disturbances is similar to that of the western Pacific disturbances. 5.) Two different paths of the African waves are found over the African Continent. The northern disturbance has a period of 4.4 days while the southern one has a period of 3.3–3.6 days. 6.) Disturbances along the northern path of the African waves are traced only to as far as 45° W, and those along the southern path are traced to the Caribbean Sea.  相似文献   

19.
Observations from the Nimbus 6 pressure modulator radiometer (PMR) have been used to estimate monthly mean planetary wave fluxes of heat and momentum in the stratosphere and mesosphere. While the eddy heat fluxes play an important role in the mean meridional circulation of the winter stratosphere they are shown to be less important in the upper mesosphere. Incorporation of the observed momentum fluxes into the Oxford two-dimensional circulation model has shown that they are incapable of providing the momentum transport necessary to balance the zonal flow accelerations induced by the mean meridional motion. Other unspecified transfer processes represented by Rayleigh frictional damping of the zonal fow are shown to dominate. In contrast the observed fluxes in the stratosphere achieve the necessary redistribution of momentum. Moreover their interannual variability profoundly influences the stratospheric circulation, as demonstrated in the model by the use of two different annual sets of observed momentum fluxes. The desirability of calculating the planetary wave behaviour within the model is indicated.  相似文献   

20.
The southwest coast of England was subjected to an unusually energetic sequence of Atlantic storms during the 2013/2014 winter, with the 8‐week period from mid‐December to mid‐February representing the most energetic period since at least 1953. A regional analysis of the hydrodynamic forcing and morphological response of these storms along the SW coast of England highlighted the importance of both storm‐ and site‐specific conditions. The key factor that controls the Atlantic storm wave conditions along the south coast of southwest England is the storm track. Energetic inshore wave conditions along this coast require a relatively southward storm track which enables offshore waves to propagate up the English Channel relatively unimpeded. The timing of the storm in relation to the tidal stage is also important, and coastal impacts along the macro‐tidal southwest coast of England are maximised when the peak storm waves coincide with spring high tide. The role of storm surge is limited and rarely exceeds 1 m. The geomorphic storm response along the southwest coast of England displayed considerable spatial variability; this is mainly attributed to the embayed nature of the coastline and the associated variability in coastal orientation. On west‐facing beaches typical of the north coast, the westerly Atlantic storm waves approached the coastline shore‐parallel, and the prevailing storm response was offshore sediment transport. Many of these north coast beaches experienced extensive beach and dune erosion, and some of the beaches were completely stripped of sediment, exposing a rocky shore platform. On the south coast, the westerly Atlantic storm waves refract and diffract to become southerly inshore storm waves and for the southeast‐facing beaches this results in large incident wave angles and strong eastward littoral drift. Many south coast beaches exhibited rotation, with the western part of the beaches eroding and the eastern part accreting. © 2015 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号