温盐环流与全球增暖的数值模拟──（一）纬向平均温盐环流的模拟

Simulation of Thermohaline Circulation and Global Warming──(I)Simulation of Zonal Mean Thermohaline Circulation

本文是用简单海一气耦合模型模拟温盐环流在全球增暖事件中作用的研究工作的第一部分。为了建立一个简单海一气耦合模型，我们首先根据Ｗｒｉｇｈｔ和Ｓｔｏｋｅｒ等人的设计复制出一个包括大西洋、太平洋和南大洋在内的二维温盐环流模式，从等温、等盐和无运动的初始状态出发，在给定的年平均海表强迫下将模式积分了４０００年，模拟出了和原作相似的温盐环流。对模拟结果的分析表明，相对于北太平洋而言，北大西洋北部的高盐、低温特点（后者是由两大洋在地理上的差别决定的）是形成当代温盐环流的主要原因；从与温盐环流相联系的海表热通量来看，北大西洋北部是向大气提供热量的主要源地；模式温盐环流对于海表盐度通量的敏感性试验的结果表明，对于纬圈平均的二维模式而言，要想模拟出合理的温盐环流就必须人为地提高北大西洋北部的海表盐度，文章分析了这种作法的物理根据；模式中的对流过程对于温盐环流的维持是至关重要的，对比有无季节循环的试验结果可以看出，虽然温度场的明显的季节变化只出现在模式的最上面两层，但由于引进季节循环后冬季高纬海洋的对流活动加强，后者直接影响到温盐环流，使更多的深海热量上传并向大气释放。这是使海洋温跃层得以保持合理．厚度的一个重要原因。

This is the first part of the work on the role of the thermohaline circulationin global warming event conducted with a simple coupled ocean-atmosphere model.In order to establish the coupled model, a two-dimensional thermohaline circulation model, which was the first formulated by Wright and Stocker in 1991, was reconstructed first. The model consists of two basins: the Atlantic and the Pacific.which are connected by the Southern Ocean. With annual mean surface forcings, the model has been integrated for 4000 years from a homogeneous and motionless state.The simulated thermohaline structure indicates that the North Atlantic is cooler and saliner than the North Pacific Ocean. It is this characteristics that accounts for the formation of present thermohaline circulation. The meridional distribution of the air-sea heat exchange shows that the northern North Atlantic is the main source for heating atmosphere. The sensitivity experiment of the thermohaline circulation to the sea surface salinity flux indicates that it is necessary to increase thesurface salinity in the northern North Atlantic to obtain the reasonable thermohaline circulation in this zonal mean two-dimensional model. This paper also give ssome explanations for this especial treatment. In addtion, the convection is crucial for the maintenance of the thermohaline circulation. By Comparing the, result of seasonal cycle with that of non-seasonal. cycle one can find that although the,apparent seasoaal temperature variation only appears within the two uppermost layers.the inclusion of seasonal cycle strengthens the convection in high latitudes in winter, which influences the thermohaline circulation directly and actuates deep sea water to transport more heat upward. This is an important factor in the maintenance of a reasonable thickness of thermocline.