大洋环流和海气相互作用的数值模拟【-】

1、第二讲风生环流的Sverdrup理论张学洪 (zxhlasg.iap.ac )13579111315171915793AtmosphereOcean.008916123Land.074074.188615.336077.500000.663923.811385.925926.991084 500 680 900 25 7512518025536011601455177521152475285032353625401544054800Sea IceSunLASG全球海洋-大气-陆面（GOALS）耦合模式热量水分动量Barotropic Stream-function(x,y)Thermohali

2、ne forcing onlyWind and thermohalineforcingBarotropic streamfunction (England , 1993)ACCKuroshio模式试验的结果表明：对于正压流来说，风应力的贡献是最主要的；热盐强迫的贡献是次要的、选择性的。模式试验是深入了解研究对象的重要手段。 小 结GFDL OGCM(Geophysical Fluid Dynamics Lab.) Bryan (1969) 海洋模式设计 Cox (1984) 向量化版本 Pacanowski (1991) MOM问题：风能够在何种程度上决定海洋环流？“Wind-Driven C

3、irculation is the circulation in the upper kilometer of the ocean forced by the wind. The circulation can be caused by local winds or by winds in other regions.”（Stewart, 2004）1. 风的强迫作用是如何传递到较深层海洋的？2. 为什么要特别指出风的强迫作用包括局地的和非局地的两个方面？ Sverdrup模型和Ekman模型 Ekman transport / pumping Sverdrup balance / trans

4、port 风生洋流的东西向分量 风应力旋度激发的Rossby波 Mass / Volume transportUnit: Sverdrup1 Sv = 106 m3s-1定常风生环流的机理动量方程 (x方向)fvg-fug 远离西边界水平粘性项可以忽略； 定常流忽略局地变化项；水平均一忽略平流项； 存在无运动深度 D0.Sverdrup 模型Ekman 模型适用范围: 海表边界层Z= 0Z=-DEZ=-D0Ekman layer风生环流层压力梯度不可忽略 !Ekman transportandEkman pumping Ekman 层方程和边界条件AtmosphereOcean(vg=0) 海

5、洋Ekman 层的解海洋Ekman层的解 Ekman layer currents (.)DEEkman volume transport北半球的 Ekman transportVEFrom Stewart (2004)小结：Ekman layerEkman layer 是风应力直接影响的海表边界层，其中垂直粘性力和科氏力起主要作用.Ekman layer的输送和风向垂直，在北半球指向风的右侧.Ekman layer 中洋流的速度随深度呈指数衰减. 问题：风应力的非均匀分布会产生什么影响？Fig. 4.1. Illustration of Ekman transport and Ekman p

6、umping, based on the eastern Pacific Ocean. (From Tomczak & Godfrey, 2001)xVEEkman层的垂直运动Ekman pumpingwG 是 Ekman pumping产生的垂直速度，反映了Ekman layer 的辐合辐散对下层环流的驱动作用。 Sverdrup 模型适用范围: 海表 无运动层Z= 0Z=-DEZ=-D0Ekman layer风生环流层这里的运动是如何产生的 ?Z= 0Z=-DEZ=-D0Curl 0？Sverdrup balance and Sverdrup transport 位涡守恒 Sverdrup

7、 balanceEkman层以下的地转经向输送Sverdrup balance / transportSverdrup balance有多种表示Z= 0Z=-DEZ=-D0Curl 0VG小结: Sverdrup balance / transportEkman层以下的水体通过南北向移动改变它的行星涡度，以平衡Ekman pumping引起的位涡度变化 .“风生环流层”的水体通过向极地(或赤道)方向的移动，将风应力提供的涡度源(或汇)转化为水体行星涡度的增加(或减小).怎样解释逆风而动的北赤道逆流？可归结为：已知南北向分量求解东西向分量观测表明热带海区以纬向风为主，故风应力旋度取决于纬向风切变

8、。xx=0 x=XNECC风应力旋度激发的非频散 Rossby 波自由波和强迫波(Meyers, 1979)Zonal wind stress正涡度源(D14, from Meyers, 1979)Month观测事实小 结风强迫的非局地作用课程材料 大气动力学参考书Holton:动力气象引论(前六章)NECC 维持机理的讨论NECC解释: 图中的风应力廓线有利于NECC维持.Ekman输送，Sverdrup输送，纬向输送连续方程NECCEkman经向输送辐散有利于Ekman层逆风流.NECCSverdrup输送辐散有利于风生环流层的逆风流.小 结在纬向风应力处于支配地位、且东边界洋流很弱的前提

9、下，赤道无风带的存在有利于深厚NECC的维持；赤道无风带北侧有利于NECC的Ekman层分量的维持.S6uT7wU8xVayXbzYcBZdC#fD!gE%hF&iH*jI(lJ-mK+nM0oN1qO2rP4sQ5tS6uT7wU9xVayXbzYcBZdC#fD!gE%hF&iH*kI(lJ-mK+nM0oN1qO2rP4sQ5tS6vT7wU9xVayXbzYcBZdC#fD!gE%hG&iH*kI(lJ-mK+nM0oN1qO2rP4sR5tS6vT7wU9xVayXbzYcBZdC#fD$gE%hG&iH*kI(lJ-mK+nM0oN1qO3rP4sR5tS6vT7wU9xVayXb

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