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1.
水库或湖泊的热分层结构是其动力与环境过程的重要研究方面,虽然很多学者针对水体分层结构和演变机理开展了大量研究,但水体通过水-气界面与大气进行热交换的过程,各气象因子的贡献机理等研究成果还很缺乏。本文基于三峡水库香溪河库湾2019年3月-2020年2月期间的水温、水位及气象等监测数据,针对水-气界面热交换过程如何影响水温垂向结构及表层水体湍流混合作用开展研究。结果表明,(1)香溪河水体年内呈高温期分层、低温期混合的基本特征,高温期混合层深度小于8 m,低温期混合层深度超过30 m。(2)太阳短波辐射是香溪河水体的主要热源,潜热通量和长波辐射是香溪河水体的主要冷源,感热通量贡献极小。(3)香溪河平均风速较弱,约为1.6 m/s,主要通过增强潜热和感热通量的方式影响水体垂向稳定性结构特征,其机械扰动作用较弱。(4)表层水体湍能通量在高温期较低(10-7m3/s3量级),此时水体处于分层状态,风应力大概率主导表层水体湍流发育;低温期表层水体湍能通量较高(10-6 m3/s3<... 相似文献
2.
We examine the seasonal mixed-layer temperature (MLT) and salinity (MLS) budgets in the Banda–Arafura Seas region (120–138°
E, 8–3° S) using an ECCO ocean-state estimation product. MLT in these seas is relatively high during November–May (austral
spring through fall) and relatively low during June–September (austral winter and the period associated with the Asian summer
monsoon). Surface heat flux makes the largest contribution to the seasonal MLT tendency, with significant reinforcement by
subsurface processes, especially turbulent vertical mixing. Temperature declines (the MLT tendency is negative) in May–August
when seasonal insolation is smallest and local winds are strong due to the southeast monsoon, which causes surface heat loss
and cooling by vertical processes. In particular, Ekman suction induced by local wind stress curl raises the thermocline in
the Arafura Sea, bringing cooler subsurface water closer to the base of the mixed layer where it is subsequently incorporated
into the mixed layer through turbulent vertical mixing; this has a cooling effect. The MLT budget also has a small, but non-negligible,
semi-annual component since insolation increases and winds weaken during the spring and fall monsoon transitions near the
equator. This causes warming via solar heating, reduced surface heat loss, and weakened turbulent mixing compared to austral
winter and, to a lesser extent, compared to austral summer. Seasonal MLS is dominated by ocean processes rather than by local
freshwater flux. The contributions by horizontal advection and subsurface processes have comparable magnitudes. The results
suggest that ocean dynamics play a significant part in determining both seasonal MLT and MLS in the region, such that coupled
model studies of the region should use a full ocean model rather than a slab ocean mixed-layer model. 相似文献
3.
Fate of three major rivers in the Bohai Sea: A model study 总被引：1，自引：0，他引：1
Hao Liu 《Continental Shelf Research》2011,31(14):1490-1499
Huanghe (Yellow River), Haihe and Liaohe are three major rivers flowing into the Bohai Sea and account for more than 80% of the freshwater and land-drained material inputs annually. The fate of three rivers in the seawaters correlates with the transport and distribution of the riverine sediments and nutrients, and further exerts a profound influence on the local marine ecosystem dynamics. Therefore, the evolution of the river plumes under the influence of the freshwater buoyancy, the tidal forcing and the wind stress are examined using a three-dimensional primitive equation ocean circulation model, independently and jointly. It is found that both tide and wind stirring can deteriorate the stabilization of the water column caused by the freshwater buoyancy; however, the processes are different. The tide stirring originates from the seafloor due to the bottom friction as the tidal wave propagates into the shallow waters, and then the turbulent kinetic energy dissipates upward. On the other hand, the wind stirring proceeds in the up-down direction. The influences of different winds on the evolution of the river plumes are also examined. Since the situation of each river mouth is different, the wind influence is also distinct. At last, the fate of three major rivers driven by the combined tidal forcing and climatology winds is reproduced, and the simulated salinity distribution shows a reasonable agreement with that observed, meaning that the river plume evolution plays a crucial role in shaping the salinity distribution in BS. 相似文献
4.
A three-dimensional hydrodynamic model is used to investigate intra-tidal and spring–neap variations of turbulent mixing, stratification and residual circulation in the Chesapeake Bay estuary. Vertical profiles of salinity, velocity and eddy diffusivity show a marked asymmetry between the flood and ebb tides. Tidal mixing in the bottom boundary layer is stronger and penetrates higher on flood than on ebb. This flood–ebb asymmetry results in a north–south asymmetry in turbulent mixing because tidal currents vary out of phase between the lower and upper regions of Chesapeake Bay. The asymmetric tidal mixing causes significant variation of salinity distribution over the flood–ebb tidal cycle but insignificant changes in the residual circulation. Due to the modulation of tidal currents over the spring–neap cycle, turbulent mixing and vertical stratification show large fortnightly and monthly fluctuations. The stratification is not a linear function of the tidal-current amplitude. Strong stratification is only established during those neap tides when low turbulence intensity persists for several days. Residual circulation also shows large variations over the spring–neap cycle. The tidally averaged residual currents are about 50% stronger during the neap tides than during the spring tides. 相似文献
5.
Numerical experiments were conducted to investigate the ocean's response to the precipitation. A squall line observed in TOGA COARE was simulated. The simulation reproduced some of the observed ocean responses to the precipitation, such as the formation of a fresh water layer, surface cooling and the variation of upper layer turbulent mixing. The precipitation-induced fresh layer can cause the vertical turbulent diffusivities to decrease from the surface to a depth of about 11–13 meters within a few hours. After the rainfall, the turbulence increases near the surface of the ocean due to the combined effect of increased shear and wind forcing, but decreases with depth due to the development of a stable layer. The main reason for the turbulence variation is the decrease in the vertical turbulence flux below the surface fresh layer because of increased static stability. Sensitivity experiments reveal that the sea-surface temperature increases faster after rainfall due to the formation of a shallow fresh water layer near the surface. 相似文献
6.
Robin Robertson 《Ocean Dynamics》2006,56(5-6):430-444
Terrain-following ocean models are being used to simulate baroclinic tides and provide estimates of the tidal fields for circulation
and mixing studies. These models have successfully reproduced elevations with most of the remaining inaccuracies attributed
to topographic errors; however, the replication of barotropic and baroclinic velocity fields has not been as robust. Part
of the problem is the lack of an adequate observational dataset in the simulated regions to compare the models. This problem
was addressed using a dataset collected during the Flow over Abrupt Topography initiative at Fieberling Guyot. To evaluate
the capability of the Regional Ocean Model System (ROMS) to simulate baroclinic tidal velocities, the combined tides for four
constituents, M2, S2, K1, and O1, were modeled over Fieberling Guyot. Model inputs, numerical schemes, and parameterizations were varied to improve agreement
with observations. These included hydrography, horizontal resolution, and the vertical mixing parameterization. Other factors
were evaluated but are not included in this paper. With the best case, semidiurnal baroclinic tides were well replicated with
RMS differences between the model estimates and the observations of 1.85 and 0.60 cm s−1 for the major axes of the tidal ellipses for M2 and S2, respectively. However, diurnal K1 baroclinic tides were poorly simulated with RMS differences of 4.49 cm s−1. In the simulations, the K1 baroclinic tides remained bottom-trapped unlike the observed fields, which had free waves due to the contribution of the
mean velocity to the potential vorticity. The model did not adequately simulate the mean velocity, and the K1 tides remained trapped. A resolution of 1 km most accurately reproduced the major axes and mean velocities; however, a 4-km
resolution was sufficient for a qualitative estimate of where baroclinic tidal generation occurred. Nine vertical mixing parameterizations
were compared. The vertical mixing parameterization was found to have minor effects on the velocity fields, with most effects
occurring over the crown of guyot and in the lower water column; however, it had dramatic effects on the estimation of vertical
diffusivity of temperature. Although there was no definitive best performer for the vertical mixing parameterization, several
parameterizations could be eliminated based on comparison of the vertical diffusivity estimates with observations. The best
performers were Mellor–Yamada and three generic length scale schemes. 相似文献
7.
Vertical mixing by the tides plays a key role in controlling water column structure over the seasonal cycle in shelf seas. The influence of tidal stirring is generally well represented as a competition between surface buoyancy input and the production of turbulent kinetic energy (TKE) by frictional stresses, a competition which is encapsulated in the Qh/u3 criterion. An alternative control mechanism arises from the limitation of the thickness of the bottom boundary layer due to the effects of rotation and the oscillation of the flow. Model studies indicate that, for conditions typical of the European shelf seas, the energy constraint exerts the dominant control but that for tidal streams with large positive polarisation (i.e. anti-clockwise rotation of velocity vector), some influence of rotation in limiting mixing should be detectable. We report here measurements of flow structure (with ADCPs) and turbulent dissipation (FLY Profiler) made at two similar locations in the Celtic Sea which differ principally in that the tidal currents rotate in opposite senses with approximately equal magnitude (polarity P=±0.6). A clear contrast was observed between the two sites in the vertical structure of the currents, the density profile and the rate of dissipation of TKE. At the positive polarity (PP) site (P≈+0.6), the bottom boundary layer in the tidal flow was limited to ∼20 mab (metre above the bed) and significant dissipation from bottom boundary friction was constrained within this layer. At the negative polarity (NP) site (P≈−0.6), the dominant clockwise rotary current component exhibited a velocity defect (i.e. reduction relative to the free stream) extending into the upper half of the water column while significant dissipation was observed to penetrate much further up the water column with dissipation levels ∼10−4.5 W m−3 reaching to the base of the pycnocline at 70–80 mab. These contrasting features of the vertical distribution of dissipation are well reproduced by a 1-D model when run with windstress and tidal forcing and using the observed density profile. Model runs with reversed polarity at the two sites, support the conclusion that the observed contrast in the structure of tidal velocity, dissipation and stratification is due to the influence of tidal stream polarity. Increased positive polarity reduces the upward penetration of mixing which allows the development of stronger seasonal stratification, which, in turn, further inhibits vertical mixing. 相似文献
8.
藏南羊卓雍错湖面大气湍流特征观测分析 总被引：2，自引：1，他引：1
湍流运动是大气边界层的本质特征,是地表与大气之间能量和物质交换的主要方式.本文利用2016和2017年4-10月藏南羊卓雍错湖泊涡动观测资料,分析了湖面大气湍流方差和湍流特征量的统计和变化特征.结果表明：（1）不稳定层结下,三维风速分量和超声虚温、水汽密度、CO2密度的无量纲标准差随稳定度变化符合Monin-Obukhov相似理论的"1/3"或"-1/3"次幂律,垂直风速的拟合效果最好;稳定层结下,除CO2密度无量纲标准差与稳定度无明显关系外,其他量基本上满足相似性规律;中性条件下,以上物理量的无量纲标准差分别趋近常数：3.57、3.93、0.77、20.91、6.35和11.96.（2）水平方向平均湍流强度（0.60和0.58）大于垂直方向（0.13）,三维方向湍流强度与平均风速的变化呈显著负相关,相关系数分别为-0.39、-0.42和-0.34.（3）湖面湍流动能随风速呈线性增长,增长率达0.45 m/s;近中性层结时湍流动能最大,层结越稳定或不稳定湍流动能均减小.（4）湖泊下午到傍晚动量输送较强,13：00-22：30时间段平均动量通量达0.091 kg/（m·s2）;热量输送以潜热为主,潜热通量日平均值（77.3 W/m2）是感热通量（14.6 W/m2）的5.3倍,感热和潜热通量日变化峰值分别出现在5：30（22.4 W/m2）和16：00（106.6 W/m2）. 相似文献
9.
10.
The influence of asymmetries in overlying stratification on near-bed turbulence and sediment suspension in a partially mixed estuary 总被引：3，自引：1，他引：2
Data collected from the York River estuary demonstrate the importance of asymmetries in stratification to the suspension and transport of fine sediment. Observations collected during two 24-h deployments reveal greater concentrations of total suspended solids during the flood phase of the tide despite nearly symmetric near-bed tidal current magnitude. In both cases, tidally averaged net up-estuary sediment transport near the bed was clearly observed despite the fact that tidally averaged residual near-bed currents were near zero. Tidal straining of the along-channel salinity gradient resulted in a stronger pycnocline lower in the water column during the ebb phase of the tide and appeared to limit sediment suspension. Indirect measurements suggest that the lower, more intense, pycnocline on the ebb acted as a barrier, limiting turbulent length scales and reducing eddy diffusivity well below the pycnocline, even though the lower water column was locally well mixed. In order to more conclusively link changes in stratification to properties of near-bed eddy viscosity and diffusivity, longer duration tripod and mooring data from an additional experiment are examined, that included direct measurement of turbulent velocities. These additional data demonstrate how slight increases in stratification can limit vertical mixing near the bed and impact the structure of the eddy viscosity below the pycnocline. We present evidence that the overlying pycnocline can remotely constrain the vertical turbulent length scale of the underlying flow, limiting sediment resuspension. As a result, the relatively small changes in stratification caused by tidal straining of the pycnocline allow sediment to be resuspended higher in the water column during the flood phase of the tide, resulting in preferential up-estuary transport of sediment.Responsible Editor: Iris Grabemann 相似文献
11.
利用美国航空航天局MERRA(Modern-Era Retrospective Analysis for Research and Applications)再分析资料和MODIS(Moderate-Resolution Imaging Spectroradiometer)卫星资料以及欧洲气象中心ECMWF-Interim(European Centre for Medium-Range Weather Forecasts)再分析资料,分析了发生于青藏高原北侧上空的一次地形重力波事件,并使用中尺度预报模式WRF-ARW.V3.0(Weather Research and Forecasting model,V3.0)对其进行了数值模拟.在此基础上,诊断分析了此次地形重力波在UTLS(Upper Troposphere and Lower Stratosphere)区域造成的物质和能量垂直传输特征.分析结果表明这一中尺度地形重力波信号的水平波长约为600km,与地形扰动水平尺度接近,重力波在对流层中传播的垂直波长约为3km,在垂直方向上随着高度的增加呈现出由东向西倾斜的结构特征.此次地形重力波上传进入平流层并在150hPa附近破碎,波破碎后动量通量在短时间内发生了强烈的衰减,重力波携带的能量在破碎高度附近释放.重力波破碎的同时垂直方向湍流混合变得异常强烈,湍流交换系数可在短时间内增加到背景值的8倍以上,剧烈湍流混合过程导致了对流层上层的空气进入平流层,使下平流层空气出现了位势涡度和臭氧的低值区,在浮力频率的垂直剖面中也可以看到由于地形重力波过程造成的平流层下层浮力频率异常低值区. 相似文献
12.
The influence of a summer storm event in 2007 on the North Sea and its effects on the ocean stratification are investigated using a regional coupled ocean (Regional Ocean Modeling System, ROMS)-atmosphere (Weather Research & Forecasting model, WRF) modeling system. An analysis of potential energy anomaly (PEA, Φ) and its temporal development reveals that the loss of stratification due to the storm event is dominated by vertical mixing in almost the entire North Sea. For specific regions, however, a considerable contribution of depth-mean straining is observed. Vertical mixing is highly correlated with wind induced surface stresses. However, peak mixing values are observed in combination with incoming flood currents. Depending on the phase between winds and tides, the loss of stratification differs strongly over the North Sea. To study the effects of interactive ocean-atmosphere exchange, a fully coupled simulation is compared with two uncoupled ones for the same vertical mixing parameters to identify the impact of spatial resolution as well as of SST feedback. While the resulting new mixed layer depth after the storm event in the uncoupled simulation with lower spatial and temporal resolution of the surface forcing data can still be located in the euphotic zone, the coupled simulation is capable to mix the entire water column and the vertical mixing in the uncoupled simulation with higher resolution of the surface forcing data is strongly amplified. These differences might have notable implications for ecosystem modeling since it could determine the development of new phytoplankton blooms after the storm and for sediment modeling in terms of sediment mobilization. An investigation of restratification after the extreme event illustrates the persistent effect of this summer storm. 相似文献
13.
A model of the wave and current boundary‐layer structure was developed using the k–ε turbulent closure model. The finite‐difference method was used to solve the governing equations. Vertical logarithmic grids and equal time steps were adopted. The following modelled simulations were obtained: (1) vertical profiles of wave velocity amplitude, eddy viscosity coefficient and turbulent kinetic energy with waves only; (2) vertical profiles of wave velocity amplitude, mean current velocity, eddy viscosity coefficient and turbulent kinetic energy with waves having a following current. To test the validity and the rationality of the present model, vertical profiles of modelled wave velocity amplitude and mean velocity were compared with corresponding experimental results available in the literature. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
14.
Measurements of turbulent fluctuations of horizontal and vertical components of velocity, salinity and suspended particulate matter are presented. Turbulent Prandtl numbers are found to increase with stratification and to become larger than 1. Consequently, the vertical turbulent mass transport is suppressed by buoyancy forces, before the turbulent kinetic energy (TKE) and vertical turbulent momentum exchange are inhibited. With increasing stratification, the buoyancy fluxes do not cease, instead they become countergradient. We find that buoyantly driven motions play an active role in the transfer of mass. This is in agreement with trends derived from Monin–Obukhov scaling. For positive Richardson flux numbers (Ri f ), the log velocity profile in the near-bed layer requires correction with a drag reduction. For negative Ri f , the log velocity profile should be corrected with a drag increase, with increasing |Ri f |. This highlights the active role played by buoyancy in momentum transfer and the production of TKE. However, the data do not appear to entirely follow Monin–Obukhov scaling. This is consistent with the notion that the turbulence field is not in equilibrium. The large stratification results in the decay of turbulence and countergradient buoyancy fluxes act to restore equilibrium in the energy budget. This implies that there is a finite adjustment timescale of the turbulence field to changes in velocity shear and density stratification. The energy transfers associated with the source and sink function of the buoyancy flux can be modeled with the concept of total turbulent energy. 相似文献
15.
Fei Dong Chenxi Mi Michael Hupfer Karl-Erich Lindenschmidt Wenqi Peng Xiaobo Liu Karsten Rinke 《水文研究》2020,34(5):1131-1143
Vertical turbulent diffusivity (Kz), which can be estimated from water temperature, is a key factor in the evolution of water quality in lentic waters. In this study, we analysed the capability of a three-dimensional hydrodynamic model (EFDC) to capture water temperature and vertical diffusivity in Lake Arendsee in the Northern German plain. Of particular interest to us is to evaluate the model performance for capturing the diffusion minimum within the metalimnion and analyse the response of the metalimnetic Kz to meteorological forcing, namely changing wind speed and warming. The comparison confirmed that the calibrated model could reproduce both stratification dynamics and vertical diffusion profiles in the lake. The model was also shown to be able to capture the duration and vertical extent of the metalimnetic diffusion minimum. The scenario results illustrate that, compared to air temperature, wind velocity appeared to be the more influential meteorological variable on the vertical exchange within the metalimnion. While increasing wind velocities mostly affected the minimum values of Kz in the metalimnion and thus led to intensified vertical exchange, the reduction of wind velocity mostly affected the depth of minimal Kz, but not its absolute value. 相似文献
16.
Integrated observations were made on the South China Sea shelf at 19°37’ N, 112°04’ E, under strong wind and heavy raining weather conditions in August 2005. Current data were obtained using a moored 150-kHz Acoustic Doppler Current Profiler, turbulent kinetic energy dissipation rate were measured with TurboMapII, and temperature was recorded by thermistor chains. Both the mixed layer thickness and the corresponding mean dissipation rate increased after the strong wind bursts. Average surface mixed layer thickness was 13.4 m pre-wind and 22.4 m post-wind, and the average turbulent dissipation rate in the mixed layer pre-wind and post-wind were 4.26 × 10?7 and 1.09 × 10?6 Wkg?1, respectively. The post-wind dissipation rate was 2.5 times larger than the pre-wind dissipation rate in the interior layer and four times larger in the intermediate water column. Spectra and vertical mode analysis revealed that near-inertial motion post-wind, especially with high modes, was strengthened and propagated downward toward the intermediate layer. The downward group velocity of near-inertial current was about 8.1 × 10?5 ms?1 during the strong wind bursts. The mean percentage of wind work transmitted into the intermediate layer is about 4.2 %. The ratio of post-wind high-mode energy to total horizontal kinetic energy increased below the surface mixed layer, which would have caused instabilities and result in turbulent mixing. Based on these data, we discuss a previous parameterization that relates dissipation rate, stratification, and shear variance calculated from baroclinic currents with high modes (higher than mode 1) which concentrate a large fraction of energy. 相似文献
17.
《国际泥沙研究》2020,35(1):27-41
Two formulae for the near-bed concentration(C_a) and the sediment vertical mixing parameter(m) are established based on a large scale wave flume experiment.The advantage of the new formulae is that the turbulent kinetic energy induced by wave breaking can be taken into account;the formula for C_a is in terms of the near-bed,time-averaged turbulent kinetic energy,and the formula for m is in terms of depth-and time-averaged turbulent kinetic energy.A new expression for suspended sediment load also is established by depth integration of the vertical distribution of the suspended sediment concentration obtained on basis of the new formulae.Equation validation is done by comparing the predicted C_a and m to measurements for different types of waves(regular wave,wave group,and irregular wave),and good agreement is found.The advantages of the proposed formulae over previous formulae also are discussed. 相似文献
18.
Based on high-resolution,Array for Real-time Geostrophic Oceanography(Argo)profiles and Sea Level Anomaly(SLA)data,this study statistically analyzes and compares turbulent diapycnal mixing profiles inside and outside mesoscale eddies in the Gulf Stream region.The result indicates that average diapycnal diffusivity at 300–540 m depths in anticyclonic eddies reaches4.0×10-5 m2 s-1.This is significantly higher than the 1.6×10-5 m2 s-1 outside eddies and 0.8×10-5 m2 s-1 in cyclonic eddies.Probabilities of diapycnal diffusivity greater than 10-4 m2 s-1 within anticyclonic and cyclonic eddies and outside eddies are29%,5%and 12%,respectively.However,magnitudes of average diapycnal diffusivity at 540–900 m depths in these three cases are of the same order,10-5 m2 s-1.Twenty-four of a total 38 anticyclonic eddies had enhanced mixing in the ocean interior,and 22 were observed during or shortly after strong winds.The coincidence between enhanced mixing and strong wind stress indicates that more wind-induced,near-inertial wave energy propagates downward in anticyclonic eddies.The deeper part of 12 profiles(below 540 m)in anticyclonic eddies had vertical overturns with Thorpe scale exceeding 5 m,among which three profiles had overturns reaching 20 m.Enhanced mixing may have occurred in deep layers of some profiles,although it was not evident in average conditions. 相似文献
19.
The validation and subsequent application of the current three-dimensional numerical hydrodynamic model of Chesapeake Bay is presented. The numerical model solves conservation equations for water mass, momentum, salinity, and heat on a boundary-fitted grid in the horizontal plane and a Cartesian z-grid in the vertical. A generalized ADI finite difference scheme is employed in conjunction with mode splitting technique, solving external and the internal modes. The 10-year boundary conditions including tide, slinity, temperature, wind, heat exchange coefficient, river and non-point source flows were constructed. Model validation was accomplished by demonstrating the model's ability to reproduce observed data over time scales ranging from tidal to seasonal periods. The major parameters compared include tidal elevation, intra-tidal and residual velocities, salinity, temperature, stratification, and flux calculated through the Bay mouth.After validation, the model was applied to simulate bay hydrodynamics for the 10 years of 1985–94. These results were used to drive the three-dimensional water quality model of Chesapeake Bay, which is discussed in a companion paper. 相似文献
20.
在美国Ｋａｎｓａｓ和Ｎｅｂｒａｓｋａ交界处于１９９２年进行的ＳＴＯＲＭ－ＦＥＳＴ（ＳＴｏｒｍ－ｓｃａｌｅ Ｏｐｅｒａｔｉｏｎａｌ ａｎｄ Ｒｅｓｅａｒｃｈ Ｍｅｔｅｏｒｏｌｏｇｙ－Ｆｒｏｎｔｓ Ｅｘｐｅｒｉｍｅｎｔ Ｓｙｓｔｅｍ Ｔｅｓｔ）资料基础上,分析了 斜压对流边界层中温度、湿度和风速的垂直分布．分析表明,在对流边界层中温度和湿度常 显示很好的混合;但风速分量有时混合很好,有时则存在切变．计算了存在和不存在风切变 两种情况下的湍流动能收支．最后,讨论了对流边界层中风切变形成的可能原因． 相似文献