南海上层环流对不同气候态风场响应的数值研究

摘要

Four kinds of climatological monthly wind stresses, including SCOW (Scatterometer Climatology of Ocean Winds), CFSR (NCEP Climate Forecast System Reanalysis), ERA-Interim (the Interim ECMWF Re-Analysis), and NCEP [the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Reanalysis 1] were used to force the South China Sea (SCS) circulation using the Regional Ocean Modeling System (ROMS). The differences among the simulated upper circulation in the SCS from the four experiments and their dynamical relationships with the differences of these wind stresses were explored. Significant differences exist in wind stress and its curl in terms of patterns, and these differences are reflected in the upper-ocean model responses. The results show that seasonal variation of the basin-scale circulation in the SCS can be well represented in all the experiments. The major differences are in sub-basin or mesoscale circulations. It is the significant local positive wind stress curl that leads to the generation of the Luzon cold eddy in winter. The dipole structure of the upper circulation off the Vietnam coast can be clearly seen in all four experiments in summer;but the strength of the dipole varies with the forcing and is related to the local wind stress curl dipole. Moreover, it is shown that the Luzon Strait transports are consistent in the experiments, which indicates that there is little impact from the differences of local wind stresses on the Luzon Strait transport. But the simulated Taiwan Strait transports differ great in both autumn and winter. Strong northeasterly wind impedes the water transport from south to north. Further analysis shows that large northward seawater transport through the Taiwan Strait in winter is in favor of the existence of the SCS warm current (SCSWC) in the northern SCS in the model results. Overall, this study helps us to more deeply understand the responses of upper-ocean circulation in the SCS to atmospheric wind forcing. At the same time, it provides some references to the choice of wind field in simulating the SCS circulation.%文章利用4种不同的气候态风场 Scatterometer Climatology of Ocean Winds (SCOW)、Climate Forecast System Reanalysis (CFSR)、the Interim ECMWF Re-Analysis (ERA-Interim)和NECP [the National Centers for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) Reanalysis 1]分别驱动区域海洋环流模式(Regional Ocean Modeling System, ROMS)以模拟南海环流,从而比较分析南海上层环流模拟结果的差异及其与风应力场之间的动力联系。结果表明,4种风场均能模拟出南海海盆尺度环流的季节变化特征,但对南海局地环流特征的模拟存在差异。分析显示,局地显著的正风应力旋度是冬季吕宋冷涡产生的根本原因；夏季越南东部海域的上层环流偶极子在模拟试验结果中均显现,但其强度与局地风应力旋度大小有关。海峡通量的模拟结果显示,吕宋海峡水体通量受海峡风场差异影响较小；台湾海峡秋冬季水体通量则有较大差别,强东北季风不利于海峡北向水体输送。此外,台湾海峡冬季较强的北向水体输送有利于南海暖流的生成。研究结果对深入理解南海上层环流对大气强迫的响应有裨益,并且可为不同目的的南海环流数值模拟时的风场选择提供参考。