The double ITCZ bias in CMIP5 models: interaction between SST, large-scale circulation and precipitation
The double ITCZ bias in CMIP5 models: interaction between SST, large-scale circulation and precipitation
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DOI：
10.1007/s00382-015-2468-6
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发表时间：
2015-02-01
期刊：
影响因子：
4.6
通讯作者：
Bellon, Gilles
中科院分区：
文献类型：
--
作者：
Oueslati, Boutheina;Bellon, Gilles
双热带辐合带（ITCZ）偏差仍然影响所有参与CMIP5（耦合模式比较计划第5阶段）的模式。就双热带辐合带而言，作为一个整体，大气环流模式在CMIP3和CMIP5之间几乎没有改进。本研究提出了一种新的面向过程的度量标准，除了现有的海表温度（SST）与双热带辐合带偏差之间的关系外，它还提供了大气过程与双热带辐合带偏差之间稳健的统计关系。使用THR - MLT指数（Bellucci等人，《气候杂志》5:1127 - 1145，2010年）来检验海表温度的贡献，该指数综合了局部海表温度表示的偏差以及导致双热带辐合带区域上升开始的海表温度阈值。作为衡量模式在模拟环流与降水相互作用方面偏差的一个度量标准，我们建议使用综合降水环流误差（CPCE）。它是通过计算每个垂直层次对热带海洋总降水贡献的二次误差得到的。CPCE是环流 - 降水耦合的一种全局度量，它表征的是模式的物理参数化，而非东太平洋的区域特征。线性回归分析表明，CMIP5耦合海洋 - 大气模式中大部分双热带辐合带的差异可归因于海表温度偏差，并且降水大尺度动力学关系解释了这些模式以及仅大气模式中偏差的很大一部分。
The double intertropical convergence zone (ITCZ) bias still affects all the models that participate to CMIP5 (Coupled Model Intercomparison Project, phase 5). As an ensemble, general circulation models have improved little between CMIP3 and CMIP5 as far as the double ITCZ is concerned. The present study proposes a new process-oriented metrics that provides a robust statistical relationship between atmospheric processes and the double ITCZ bias, additionally to the existing relationship between the sea surface temperature (SST) and the double ITCZ bias. The SST contribution is examined using the THR-MLT index (Bellucci et al. in J Clim 5:1127-1145, 2010), which combines biases on the representation of local SSTs and the SST threshold leading to the onset of ascent in the double ITCZ region. As a metrics of a model's bias in simulating the interaction between circulation and precipitation, we propose to use the Combined Precipitation Circulation Error (CPCE). It is computed as the quadratic error on the contribution of each vertical regime to the total precipitation over the tropical oceans. CPCE is a global measure of the circulation-precipitation coupling that characterizes the model physical parameterizations rather than the regional characteristics of the eastern Pacific. A linear regression analysis shows that most of the double ITCZ spread among CMIP5 coupled ocean-atmosphere models is attributed to SST biases, and that the precipitation large-scale dynamics relationship explains a significant fraction of the bias in these models, as well as in the atmosphere-only models.