Numerical study of the meridional overturning circulation with “mixing hotspots” in the Pacific Ocean     

Takahiro Endoh  Toshiyuki Hibiya 《Journal of Oceanography》2006,62(3):259-266

Using an idealized ocean general circulation model, we examine the effect of “mixing hotspots” (localized regions of intense diapycnal mixing) predicted based on internal wave-wave interaction theory (Hibiya et al., 2006) on the meridional overturning circulation of the Pacific Ocean. Although the assumed diapycnal diffusivity in the mixing hotspots is a little larger than the predicted value, the upwelling in the mixing hotspots is not sufficient to balance the deep-water production; out of 17 Sv of the downwelled water along the southern boundary, only 9.2 Sv is found to upwell in the mixing hotspots. The imbalance as much as 7.8 Sv is compensated by entrainment into the surface mixed layer in the vicinity of the downwelling region. As a result, the northward transport of the deep water crossing the equator is limited to 5.5 Sv, much less than estimated from previous current meter moorings and hydrographic surveys. One plausible explanation for this is that the magnitude of the meridional overturning circulation of the Pacific Ocean has been overestimated by these observations. We raise doubts about the validity of the previous ocean general circulation models where diapycnal diffusivity is assigned ad hoc to attain the current magnitude suggested from current meter moorings and hydrographic surveys.  相似文献   

Mean flow and variability in the southwestern East Sea     

Kyung-Il Chang  Nelson G. Hogg  Moon-Sik Suk  Sang-Kyung Byun  Young-Gyu Kim  Kuh Kim 《Deep Sea Research Part I: Oceanographic Research Papers》2002,49(12)

The Ulleung Basin is one of three deep basins that are contained within the East/Japan Sea. Current meter moorings have been maintained in this basin beginning in 1996. The data from these moorings are used to investigate the mean circulation pattern, variability of deep flows, and volume transports of major water masses in the Ulleung Basin with supporting hydrographic data and help from a high-resolution numerical model. The bottom water within the Ulleung Basin, which must enter through a constricted passage from the north, is found to circulate cyclonically—a pattern that seems prevalent throughout the East Sea. A strong current of about 6 cms⁻¹ on average flows southward over the continental slope off the Korean coast underlying the northward East Korean Warm Current as part of the mean abyssal cyclonic circulation. Volume transports of the northward East Korean Warm Current, and southward flowing East Sea Intermediate Water and East Sea Proper Water are estimated to be 1.4 Sv (1 Sv=10⁻⁶ m³ s⁻¹), 0.8 Sv, and 3.0–4.0 Sv, respectively. Deep flow variability involves a wide range of time scales with no apparent seasonal variations, whereas the deep currents in the northern East Sea are known to be strongly seasonal.  相似文献   

Determining the age of water and long-term transport timescale of the Chesapeake Bay   总被引：5，自引：0，他引：5  

Jian Shen  Harry V. Wang 《Estuarine, Coastal and Shelf Science》2007,74(4):585-598

The concept of age of water (AW) is applied to the Chesapeake Bay to investigate the long-term transport properties for dissolved substances. A real-time calibrated hydrodynamic Chesapeake Bay model in 3 Dimensions (CH3D), employing a boundary-fitted curvilinear grid, is used for the study. The long-term transport properties, represented by AW, are investigated under the conditions of low river inflow of 1995 and high river inflow of 1996, as well as for constant mean inflows. The influences of freshwater, density-induced circulation, and wind-induced transport on age distribution have been investigated. Model results show that river inflows, wind stress, and density-induced circulation play important roles in controlling the long-term transport in the Bay. The model results shows that it requires 120–300 days for a marked change in the characteristics of the pollutant source discharged into the Bay from the Susquehanna River to affect significantly the conditions near the mouth under different hydrodynamic conditions. An increase of river discharge results in increases of downstream residual current and gravitational circulation, and thus reduces AW. The density-induced circulation contributes to the transport substantially. The dissolved substances discharged into the Bay are transported out of the Bay more rapidly when the estuary becomes more stratified. Southeasterly and southwesterly winds have strong impacts on the transport compared to the northeasterly and northwesterly winds. The former increases lateral and vertical mixing significantly. Consequently, the gravitational circulation is reduced and the transport time is increased by 50%. The model results provide useful information for understanding the long-term transport processes in the Bay.  相似文献   

Ice Sheet-Thermohaline Circulation Interactions in a Climate Model of Intermediate Complexity   总被引：3，自引：0，他引：3  

Zhaomin Wang  Lawrence A. Mysak 《Journal of Oceanography》2001,57(4):481-494

A vertically integrated dynamic ice sheet model is coupled to the atmosphere-ocean-sea ice-land surface climate model recently developed by Wang and Mysak (2000). The background lateral (east-west) ice sheet discharge rate used by Gallee et al. (1992) is reduced and the planetary emissivity is increased (to parameterize the cooling effect of a decrease of the atmospheric CO₂ concentration), in order to build up substantial ice sheets during a glacial period and hence set the stage for ice sheet-thermohaline circulation (THC) interactions. The following iceberg calving scheme is then introduced: when the maximum model height of the North American ice sheet reaches a critical value (2400 m), a prescribed lateral discharged rate is imposed on top of the background discharge rate for a finite time. Per a small prescribed discharge rate, repeated small iceberg calving events occur, which lead to millennial-scale climate cycles with small amplitudes. These are a crude representation of Dansgaard-Oeschger oscillations. Over one such cycle, the zonally averaged January surface air temperature (SAT) drops about 1.5°C at 72.5°N. However, a large prescribed lateral discharge rate leads to the shut down of the THC. In this case, the January SAT drops about 5°C at 72.5°N, the sea ice extent advances equatorward from 57.5° to 47.5°N and the net ice accumulation rate at the grid of maximum ice sheet height is reduced from 0.24 to 0.15 m/y. Since data strongly suggest that a collapsed THC was not a steady state during the last glacial, we restore the THC by increasing the vertical diffusivity in the North Atlantic Ocean for a finite time. The resulting climate cycles associated with conveyor-on and conveyor-off phases have much larger amplitudes; furthermore, the strong iceberg calving events lead to a larger loss of ice sheet mass and hence the period of the oscillations is longer (several thousand years). This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

科氏力对河口分汊的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

金元欢  沈焕庭 《海洋科学》1993,17(4):52-56

以长江口、黄河口、珠江口、闽江口等几个分汊河口为例,分析了科氏力在河口分汊中的作用。结果表明,涨落潮流路分歧主要通过形成涨落潮冲刷槽和中央缓流区浅滩而逐渐使河口产生分汊;水面横比降则以横向环流和横向切滩两种形式,或堆积或冲刷,导致河口分汊。  相似文献   

太平洋年代际海洋变率研究进展   总被引：10，自引：1，他引：10  

王东晓  谢强  刘赟  刘钦燕  杜岩 《热带海洋学报》2003,22(1):76-83

随着“气候变率与可预报性研究”（CLIVAR计划）的实施，年代际气候变率研究已经成为国际气候研究的一个新热点，由于海洋特别是海洋次表层具有巨大的热损性，海洋环流在年代际气候变率中所起的作用已得到越来越多的重视。但迄今为止，海洋以什么方式参与到年代际气候变化中，海洋次表层在年际和年代际时间尺度上起到什么作用这些与海洋环流有关的问题仍未得到解决，而这些问题的解决将有助于建立一种完备的年代际气候变化机制的理论，文章通过对近10a来国内外在该领域内研究进展的回顾，提出了一个关于太平洋年际变化（如ENSO循环）和年代际变化（如PDO循环）相互作用的猜想，为今后在国内开展相关研究提供了一些设想。  相似文献   

南海季风区地域性大气环流的结构     

周发琇  张涛  高荣珍 《中国海洋大学学报(自然科学版)》2001,31(4):467-472

作者使用 NCEP/ NCAR再分析资料 ,在热带 30°S～ 30°N纬带用谐波分析方法分离出超长波之后 ,再采用环流诊断方法 ,发现南海季风区存在地域性环流系统。文中给出冬、夏季风期该系统的三维空间结构和相应的热源分布 ,讨论了该地域性环流系统对南海季风气候及其异常的作用 ,并探讨夏季风爆发北部先于南部的一种可能的气候原因。  相似文献   

1998年春夏南海温盐结构及其变化特征   总被引：11，自引：2，他引：11  

王凡  赵永平  冯志纲  白学志  吴爱明 《海洋学报》2001,23(5):1-13

利用1998年5～8月“南海季风试验”期间“科学1”号和“实验3”号科学考察船两个航次CTD资料,分析了1998年南海夏季风暴发前后南海主要断面的温盐结构及其变化特征.观测发现,南海腹地基本被典型的南海水团所控制,但在南海东北部尤其是吕宋海峡附近,表层和次表层水明显受到西太平洋水的影响.季风暴发以后,南海北部表面温度有显著升高,升幅由西向东递减,而南海中部和南部表面温度基本没变,这使得南海北部东西向温度梯度和整个海盆南北向温度梯度均减小.北部断面表层盐度普遍由34以上降低到34以下,混合层均有所发展,是季风暴发后降水和风力加剧的结果.观测期间黑潮水跨越吕宋海峡的迹象明显但变化剧烈.4～5月,黑潮次表层水除在吕宋海峡中北部出现外,在吕宋岛以西亦有发现,表明有部分黑潮水从吕宋海峡南端沿岸向西进而向南进入南海.6～7月,次表层高盐核在吕宋海峡中北部有极大发展,但在吕宋岛以西却明显萎缩;虽然看上去黑潮水以更强的流速进、出南海,但对南海腹地动力热力结构的影响未必更大.一个超过34.55的表层高盐水体于巴拉望附近被发现,似与通过巴拉望两侧水道入侵南海的西太平洋水有关.  相似文献   

2021年10月山西一次罕见持续性强降水过程物理机制分析     

乔钰  赵桂香  王妍 《沙漠与绿洲气象(新疆气象)》2024,18(2)

利用气象观测资料、NCEP/NCAR 1°×1°再分析资料以及GDAS资料,对2021年10月2-7日山西持续性强降水天气过程进行分析。结果表明：稳定的乌拉尔山低槽后部冷空气扩散,中纬度短波槽东移,与副热带高压外围西南暖湿气流持续交汇,同时高低空急流耦合形成强烈上升运动,低层切变线和地面辐合线稳定维持,及低层水汽不断输送并形成辐合,为持续性强降水的发生发展提供有利动力和水汽条件。此次强降水过程分为对流性降水和稳定性降水2个阶段,2阶段水汽输送通道的源地、路径、高度均有明显差异,但水汽输送贡献率均以对流层中低层山西南侧的水汽输送占主导地位。降水开始前,对流层中上层存在对称不稳定,大气可降水量明显跃增;对流性降水阶段,干空气不断入侵,对流不稳定快速建立与释放,对流层中低层水汽辐合区与强上升气流配合,导致山西出现强对流天气。地形的阻挡、抬升及地形收缩作用,对局地极端强降水具有增幅作用。  相似文献   

南海西部浮游有孔虫记录的MIS 3期表层海洋环境变化          下载免费PDF全文

杨文瑜  黄宝琦  肖洁  周力平 《第四纪研究》2008,28(3):437-446

对南海西部越南岸外上升流区17954-2站浮游有孔虫属种组合变化、浮游有孔虫氧同位素、AMS14C测年的分析以及浮游有孔虫表层海水温度、温跃层转换函数的研究结果表明:在MIS3期,南海西部表层海水温度大体呈现暖-冷-暖的变化趋势;温跃层深度由浅到深阶段性变化;短时间尺度上温度与温跃层发生幅度较大的快速变化。暖事件（IS）对应于浮游有孔虫暖水种、混合层属种含量的增加,冷水种、温跃层属种含量的减少以及冬夏SST的升高;冷事件则与之相反。表层海水生产力亦大致呈现3个阶段（61～51ka,51～42ka和42～32ka）的变化,在千年尺度的快速气候事件中,暖事件对应浮游有孔虫生产力属种含量降低,冷事件对应升高。此外,在MIS3内部分暖事件（IS6和IS11～13）表现出表层海水温度降低,温跃层深度变浅和表层海水生产力升高的状况,表明该区此时上升流的存在,其形成原因推测是由于东亚夏季风加强的结果。  相似文献