耦合模式热带太平洋云—气候反馈模拟误差评估

Assessment of Cloud-Climate Feedback Simulation Bias of Coupled Ocean-Atmosphere Model in the Tropical Pacific

云—气候反馈是热带海气相互作用的重要过程,同时也是气候模拟的难点。本文利用IPCCAR4提供的耦合模式20世纪模拟试验结果和观测资料,通过滤波和经验正交展开(EOF)的方法将热带太平洋海表温度的年际变化和年代际变化信号分别提取出来,然后再分别计算观测和模式在年际和年代际时间尺度上云—辐射和热通量反馈特征,发现在上述两个时间尺度上,耦合模式模拟的云—辐射和热通量的反馈都要比观测和再分析资料的偏弱。反馈偏弱的可能原因是模式中热带大气对流和云对海表温度变化的敏感性比真实大气要偏弱。值得注意的是,尽管耦合模式热带太平洋年代际热力反馈偏弱,但是耦合模式模拟的热带太平洋南北纬10°之间海表温度的年代际增温趋势与观测相当。进一步分析表明,只用年代际热力反馈来解释热带太平洋的气候变化是不够的,还必须考虑动力反馈对于海表温度变化的调节作用。

Cloud-climate feedback is an important process of air-sea interaction and it is a primary difficulty of climate simulation.By using results of the 20C3M coupled ocean-atmosphere models from the IPCC AR4（Fourth Assessment Report of the Intergovernmental Panel on Climate Change） and observed data,interannual and interdecadal signals of the tropical Pacific sea surface temperature（SST） were extracted with the methods of filtering and Empirical Orthogonal Function（EOF）.Then the authors calculated interannual and interdecadal cloud and heat flux feedback.Both interannual and interdecadal cloud and heat flux feedback of coupled ocean-atmosphere models are weaker than that from the reanalysis and observed data.The weakness may be caused by weaker sensitivity of tropical convection and cloud-to-SST change of coupled ocean-atmosphere models than real ocean-atmosphere.Though interdecadal thermodynamical feedback of coupled ocean-atmosphere models is weaker,SST interdecadal warming trend of coupled ocean-atmosphere models in the tropical Pacific between 10°S and 10°N is equivalent to the observed data.Only interdecadal thermodynamical feedback is not enough to explain the climate change of the tropical Pacific,the interdecadal dynamical feedback effect also must be considered.