Estimates of subtidal volume flux in mid-Chesapeake Bay     

Mário E.C. Vieira 《Estuarine, Coastal and Shelf Science》1985,21(3):411-427

Utilizing 20 days of current meter and sea level elevation records taken in two cross-sections in mid-Chesapeake Bay an objective interpolation procedure was devised to allow the computation of vertical profiles of the laterally integrated subtidal volume fluxes at each section, at 3-h intervals over the period of the experiment. The presence of a classical mean estuarine circulation was observed; however, departures from this gravitational circulation were revealed on a shorter time scale, reaching the value of 20 000 m³ s^?1 over a day, and featuring behaviors of reverse estuarine, storage and discharge modes.The volume flux computations through each cross-section based on the measured current velocities, the freshwater inflow and the calculated Stokes transport were in agreement with each other. A two-layered box model of the mean subtidal circulation in the segment of the estuary bound by the two cross-sections is offered.A comparison was made between the computations of net volume flux into and out of the Bay above these sections using two independent methods: (1) the accounting of volume continuity based upon direct measurements of volume flux through the sections; and (2) the direct calculation of the time rate of change of volume of the upper Bay obtained from tide gauge records. The agreement between the two results was found to be very good. Further evidence is provided for the upward phase propagation of the oscillations in the residual motion of estuarine waters.  相似文献   

Longitudinal transport in a coastal lagoon     

Ned P. Smith 《Estuarine, Coastal and Shelf Science》1990,31(6)

A two-dimensional, finite difference numerical model is used to describe longitudinal transport through a transverse cross section into and out of the northern segment of Indian River lagoon, along the Atlantic coast of Florida. The model uses four layers to represent the Atlantic Intracoastal Waterway, and two layers in the shallow waters east and west of the waterway to quantify transport. Simulations during a 161-day period from late June through late November 1983 include a seasonal shift in the longitudinal component of the wind. Transport is in the same sense throughout the cross section 32% of the time. Relatively subtle lateral shear, however, has a profound effect on long-term net transport. For most of the study, cumulative net transport in the shallow areas on either side of the waterway follows the cumulative along-channel windstress, but it is directed upwind in the lower half of the Intracoastal Waterway. Four numerical experiments examine the relative importance of terms in the momentum equation and components of the database. Results suggest that time-varying baroclinic forcing is an important component of the pressure gradient. Simulations which ignore water-level variations at the open end of the model differ substantially from those which incorporate water-level fluctuations.  相似文献   

Kinetic Energy Budgets during the Rapid Intensification of Typhoon Rammasun (2014)     

Xin QUAN  Xiaofan LI 《大气科学进展》2023,40(1):78-94

In this study, Typhoon Rammasun(2014) was simulated using the Weather Research and Forecasting model to examine the kinetic energy during rapid intensification(RI). Budget analyses revealed that in the inner area of the typhoon,the conversion from symmetric divergent kinetic energy associated with the collocation of strong cyclonic circulation and inward flow led to an increase in the symmetric rotational kinetic energy in the lower troposphere. The increase in the symmetric rotational kinetic e...  相似文献   

青岛地区8月一次海风环流实例分析和WRF模拟   总被引：6，自引：2，他引：4  

孙贞  高荣珍  张进  徐晓亮  盛春岩 《气象》2009,35(8):76-84

根据青岛地区2006年8月份浮标站、岸基站和陆地站观测资料及探空加密测风资料,分析了8月21日到22日一次典型的海、陆风环流过程,并进行了WRF数值模拟和检验分析.观测数据分析表明:海、陆风环流在垂直方向分别具有闭合环流,海风环流发展高度远高于陆风环流,海风环流午后发展最强盛,海风在底层最先发展并在底层最先消失,风速大小随高度减小,发生海风环流时青岛站与浮标站的海陆气温差在4℃以上,海风环流向内陆推进大约40多千米;WRF模式较好地模拟了海风环流发生发展的完整过程,并揭示了海风环流与半岛北部相向风场的相互作用,在半岛中部地区存在辐合上升区.  相似文献   

大气环流降尺度因子在中国东部夏季降水预测中的作用   总被引：16，自引：2，他引：14  

魏凤英  黄嘉佑 《大气科学》2010,34(1):202-212

本文将1951～2007年500 hPa 格点资料构成的表征区域系统的环流特征量作为降尺度因子, 使用降尺度技术和偏最小二乘回归方法, 以环流特征量作为因子场, 建立逐月的我国东部夏季降水量的预报模型。从最佳预报模型中的环流特征量出现频率的角度, 对大气环流降尺度因子在我国东部夏季降水预测中的作用进行分析研究。结果表明, 在夏季各个月份的预报模型中, 出现频率表现最突出的因子是北半球和东半球副高系统。此外, 东亚地区副高系统也起十分重要的作用, 特别是西太平洋副高强度和面积指数。  相似文献   

Simulations of the motion of tropical cyclone-like vortices in the presence of synoptic and mesoscale circulations     

罗哲贤  平凡 《大气科学进展》2012,29(3):519-528

Initial mesoscale vortex effects on the tropical cyclone(TC) motion in a system where three components coexist(i.e.,an environmental vortex(EV),a TC,and mesoscale vortices) were examined using a barotropic vorticity equation model with initial fields where mesoscale vortices were generated stochastically.Results of these simulations indicate that the deflection of the TC track derived from the initial mesoscale vortices was clearly smaller than that from the beta effect in 60% of the cases.However,they may have a more significant impact on the TC track under the following circumstances.First,the interaction between an adjacent mesoscale vortex and the TC causes the emergence of a complicated structure with two centers in the TC inner region.This configuration may last for 8 h,and the two centers undergo a cyclonic rotation to make the change in direction of the TC motion.Second,two mesoscale vortices located in the EV circulation may merge,and the merged vortex shifts into the EV inner region,intensifying both the EV and steering flow for the TC,increasing speed of the TC.  相似文献   

Biological and physical impacts of ageostrophic frontal circulations driven by confluent flow and vertical mixing     

Takeyoshi Nagai  Amit Tandon  Nicolas Gruber  James C. McWilliams 《Dynamics of Atmospheres and Oceans》2008,45(3-4):229

Subduction, upwelling, and phytoplankton blooms are commonly observed features at oceanic fronts. This study isolates the role of vertical mixing for enhanced production and water mass subduction near fronts, considering the time-developing problem with a Semi-Geostrophic circulation model coupled to a planktonic ecosystem model. Our model results show that vertical mixing in the surface boundary layer strongly modifies the time evolution of the front and of its associated biology. Ageostrophic flows caused by the combined effects of confluence and vertical mixing enhance primary production on the less dense side and increase water mass subduction on the dense side of the front. Confluence alone results in the intensification of the front by the same advective response, while the phytoplankton bloom on the less dense side does not arise without vertical mixing. Vertical mixing alone slumps the front near the surface and provides weak subduction on the dense side and uplift of the isopycnals at the center of the front. We find that it is possible to sustain an isolated phytoplankton patch above the domed isopycnals at the center of the front with the nutrients supplied by the secondary circulations arising due to vertical mixing. These results suggest that the phytoplankton bloom and patches found on the less dense side of fronts in many field observations are likely caused by fine-scale along-isopycnal upwelling of nutrients forced by adiabatic confluence in the meander trough of fronts and further pumping and entrainment of nutrients by the secondary circulation due to vertical mixing. Isolated patches observed at the center of the front in many frontal surveys could be caused by secondary flows due to vertical mixing.  相似文献   

Downwelling and upwelling regimes: Connections between surface fronts and abyssal circulation     

Carol Anne Clayson  Maria Luneva  Philip Cunningham   《Dynamics of Atmospheres and Oceans》2008,45(3-4):165

Recent observations in the Sea of Japan show evidence of convection to a depth of roughly 1000 m in the winter of 2000, situated along the polar front. Numerical simulations have shown that this deep mixing is associated with both ageostrophic frontal circulations and pre-existing larger-scale downwelling regimes. The downwelling regimes appear to be a result of interactions between frontal meandering and deep circulation in this basin over bottom topography anomalies. The coupling between the frontal dynamics and the deep circulation are explored by analogy to atmospheric frontal circulations through the semigeostrophic Sawyer–Eliassen equation, solved numerically for the case of the Sea of Japan. As in the atmospheric case, a vertical coupling between the upper and lower circulations can produce a localized region of downwelling that can be conducive to deeper mixing than that forced solely from surface fluxes.  相似文献   

Effect of Stokes drift on upper ocean mixing   总被引：1，自引：0，他引：1  

LI Shuang  SONG Jinbao  SUN Qun 《海洋学报(英文版)》2008,27(2):11-20

Stokes drift is the main source of vertical vorticity in the ocean mixed layer. In the ways of Coriolis - Stokes forcing and Langmuir circulations, Stokes drift can substantially affect the whole mixed layer. A modified Mellor-Yamada 2. 5 level turbulence closure model is used to parameterize its effect on upper ocean mixing conventionally. Results show that comparing surface heating with wave breaking, Stokes drift plays the most important role in the entire ocean mixed layer, especially in the subsurface layer. As expected, Stokes drift elevates both the dissipation rate and the turbulence energy in the upper ocean mixing. Also, ilffluence of the surface heating, wave breaking and wind speed on Stokes drift is investigated respectively. Research shows that it is significant and important to assessing the Stokes drift into ocean mixed layer studying. The laboratory observations are supporting numerical experiments quantitatively.  相似文献   

Tidal and residual currents around a Norfolk Sandbank     

M.J. Howarth  J.M. Huthnance 《Estuarine, Coastal and Shelf Science》1984,19(1):105-117

Currents on either side of Well Bank were recorded for 41 days in May–June 1981, in order to distinguish locally tidally-generated asymmetries (pertinent to maintenance of the bank) from larger-scale and wind-driven flows.Semi-diurnal currents were dominant, nearly rectilinear and slightly inclined to the bank axis.Fourth-diurnal currents were consistent with previously observed and computed fourth-diurnal tides for the area overall; amplitudes varied as the square of the semi-diurnal amplitude. Hence they appear to be generated by tides, but only a small part locally.Residual currents (average over a tidal cycle) were always in the sense of clock-wise circulation around the bank, consistent with simple models and giving strong evidence of local generation by tides. This circulation combines with the semidiurnal currents to maintain the bank. The slow increase of the residuals with the semi-diurnal amplitude is interpreted as an effect of strong semi-diurnal currents. A persistent component onto the bank 7 m above the bottom at one position may indicate distortion of the frictional layer by the sloping bottom or by bank curvature.  相似文献