全球海气耦合模式中热盐环流对大气强迫的响应

ADJUSTMENT OF THE NORTH ATLANTIC THERMOHALINE CIRCULATION TO THE ATMOSPHERIC FORCING IN A GLOBAL AIR-SEA COUPLED MODEL

  • 摘要: 大气环流与热盐环流(THC)变化之间的因果关系,是海气相互作用研究领域的一个悬而未决的问题。作者利用一个全球海气耦合模式-挪威卑尔根气候模式(BCM)的300a积分结果,讨论了冬季北大西洋涛动(NAO)对海洋的强迫与热盐环流的年际调整之间的关系。结果发现,在NAO活动的正位相,伴随着中纬度西风带的加强,北大西洋拉布拉多海热通量损失剧增,同时海表盐度出现正距平,二者的共同作用,令表层海水变沉、密度增大,海洋层结出现不稳定,导致深对流发生。在NAO活动达到最强劲状态之后3个月,拉布拉多海对流也达到最深。北大西洋热盐环流强度变化对拉布拉多海对流活动的响应,要滞后3a左右。而在年际尺度上,大西洋的极向热输送变化和热盐环流的变化则基本是同步的。对流活动对大气存在明显的反馈作用。在对流活动深度达到最大之后1~4个月,对流热释放令拉布拉多海表层气温明显升高。

     

    Abstract: Interannual scale adjust ment of the thermohaline circulation(THC) to the forcing of the North Atlantic Oscillation(NAO) is examined by using the out put of the recently finished 300 years integration of the Bergen Climate Model(BCM).The results show that a positive phase NAO and thereby an intensified westerlies enhances the net heat flux loss of the Labrador Sea, in conjunction with the positive salinity anomaly over there, water at the surface then becomes denser, and deep convection occurs.Three months after the NAO reaches its maximum state, the Labrador Sea convection reaches its largest depth.Response of the North Atlantic thermohaline circulation to the Labrador Sea convection lags 3 years in the model.The oceanic pole ward heat transport has a maximum simult aneous correlation with the THC.In addition, feedback of the convection on the atmosphere in the model is detected.One to four months after the convection reaches its largest depth, the convective heat release leads to a warmer surfaceair over the Labrador Sea.

     

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