海气耦合模式CESM1中热带印度洋SST模拟偏差的来源分析

摘要

热带海表温度(SST)模拟偏差是困扰海气耦合模式发展的经典问题之一,其原因仍不完全清晰.针对海气耦合模式CESM1 (Community Earth System Model version 1)模拟的热带印度洋SST偏差,我设计了单独大气陆面模式、单独海洋海冰模式以及海气耦合模式等一系列数值实验.在此基础上,采用大气-陆面模式和海洋-海冰模式隐式(implicit) SST偏差的分析方法,诊断了CESM1模拟的热带印度洋SST偏差的来源,并分析了大气模式和海洋模式中影响热带印度洋上层海温模拟的主要因素.通过分析热带印度洋不同地区SST的模拟偏差来源,发现耦合模式CESM1中孟加拉湾SST模拟偏冷主要是由海洋-海冰模式中过强的垂直混合、平流作用等海洋动力偏差引起的.在阿拉伯海和赤道西印度洋,过多的潜热释放导致SST降低,大气-陆面模式模拟误差是这两个海域SST冷偏差的主要来源.对于赤道中印度洋,潜热通量偏差和垂直混合、平流作用等模拟误差共同影响上层海水温度,潜热释放偏少、海水垂直混合偏弱以及经向平流向南输送过多暖水使耦合模式模拟的赤道中印度洋SST出现暖偏差,而在赤道东印度洋,模拟的SST偏冷是由大气-陆面模式中短波辐射偏少和海洋-海冰模式中海水垂直混合过强引起的,潜热通量偏差影响较小.分析表明,耦合模式中海气相互作用只影响SST模拟偏差的大小,但不是引起SST偏差的根本原因.%Bias in simulated tropical sea surface temperature (SST) is one of common problems in coupled ocean-atmosphere models,and the reason for it is still not clear.In order to identify the causes of the SST bias in Community Earth System Model version 1 (CESM1),three numerical experiments based on atmosphere-land model,ocean-sea ice model and ocean-atmosphere coupled model are designed.Then implicit SST biases in atmosphere-land and ocean-sea ice model are utilized to analyze the source of SST biases in the tropical Indian Ocean.Results show that both the atmosphere-land model and ocean-sea ice model of CESM1 contain large errors and contribute to SST biases in different regions of the Indian Ocean.The biases related to ocean dynamics,vertical entrainment and advection in ocean-sea ice model,lead to cold SST biases in the Bay of Bengal.While excessive release of latent heat in the atmosphere-land model is the major source of cold SST biases in the Arabian Sea and western tropical Indian Ocean.In the central equatorial Indian Ocean,less latent heat release in the atmosphere-land model,weaker vertical entrainment and meridional advection in the ocean-sea ice model cause the warm SST biases,while the less shortwave radiation and stronger vertical entrainment is the main cause of cold SST biases in eastern tropical Indian Ocean.Further analysis shows that the air-sea feedback can only influence the magnitude of SST biases but not the fundamental source of SST biases.