洋际交换及其在全球大洋环流中的作用：MOM4p1积分1400年的结果
Interbasin exchanges and their roles in global ocean circulation: A study based on 1400 years' spin up of MOM4p1
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摘要: 利用非Boussinesq近似下MOM4p1的全球大洋环流预后模式，采用真实地形，以静止状态为初始条件，进行了1 400 a积分，以研究平衡状态下大洋环流的结构。模式由月平均气候态强迫场驱动，包括192×189个水平网格和压力坐标下的31个垂直层次。着重研究达到平衡状态后，各洋际通道处的质量、热量输运和补偿及其在全球大洋环流中的作用。根据动能演变特征表明，积分过程分为3个阶段：风海流的成长及准稳定状态;热盐环流的成长过程以及热盐环流的稳定状态;由静止状态冷启动达到热盐环流的稳定状态，积分过程必须在千年以上。模式结果再现了从白令海峡到格陵兰海的北冰洋贯穿流和印度尼西亚贯穿流，并用已有观测资料对它们进行对比。分析表明，海面的倾斜结构是形成太平洋-北冰洋-大西洋贯穿流和印尼贯穿流的主要动力机制。分析指出，尽管在北大西洋存在1.4×106 m3/s的南向体积输运，但其热量输运却是北向的并达到1015W量级，其原因是北向的上层海流温度远高于北大西洋深层水向南的回流。文章分析了经向体积和热量输运对北大西洋深层水补偿来源及大西洋经向翻转环流的贡献。模拟所得洋际交换的量值可以由经向补偿予以合理解释，并得到以往实测与数模结果的支持。洋际通道处的体积和热量交换突出体现了其在大洋传送带系统中的枢纽作用。Abstract: A global prognostic model based on Mom4p1,which is a primitive equation nonBoussinesq numerical model,has been integrated 1 400 years from the state of rest based on the realistic topography to study the long term pattern of combined wind-driven and thermodynamically-driven general circulation.The model is driven by monthly climatological mean forces and includes 192×189 horizontal grids and 31 pressure based vertical levels.The main objective is to investigate the mass and heat transports at interbasin passagesand their compensations and roles in the global ocean circulation under equilibrium state of long term spin up.The kinetic energy analysis divides the spin up process into three stages:the quasi-stable state of wind driven current,the growing phase of thermodynamical circulation and the equilibrium state of thermohaline circulation. It is essential to spin up over a thousand years in order to reach the thermohaline equilibrium state from a state of rest. The Arctic Throughflow from the Bering Strait to the Greenland Sea and the Indonesian Throughflow(ITF) are captured and examined with their compensations and existing data. Analysis reveals that the slope structures of sea surface height are the dynamical driving mechanism of the Pacific-Arctic-Atlantic throughflow and ITF. The analysis denotes,in spite of 1.4×106 m3/s of the southward volume transport in the northern Atlantic,there is still 1×1015W of heat transported northward since the northward currents in upper layer carry much higher temperature water than the southward flowing northern Atlantic deep water(NADW).Meridional volume and heat transports are focused on the contributions to NADW renewals and Atlantic meridional overturning circulation(AMOC). Quantitative descriptions of the interbasin exchanges are explained by meridional compensations and supported by previous observations and numerical modeling results. Analysis indicates that the volume and heat exchanges on the interbasin passages proposed in this article manifest their hub roles in the Great Ocean Conveyor system.
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