双月刊

ISSN 1006-9895

CN 11-1768/O4

FGOALS耦合模式对赤道太平洋海温和降水年循环的模拟评估
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1.中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室LASG;2.中国科学院大学

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中国科学院战略先导专项项目,国家自然科学基金


Evaluation of FGOALS in Simulating the Annual Cycle of Tropical Pacific Rainfall and SST
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    摘要:

    本文评估了中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG/IAP)研发的全球气候系统模式(FGOALS)的4个版本(FGOALS-g2, s2, g3, f3-L)对赤道太平洋地区的海温、降水气候态和季节循环的模拟能力。其中前2个版本g2,s2和后2个版本g3, f3-L分别完成了国际耦合模式比较计划第五阶段(CMIP5)和第六阶段(CMIP6)数值试验并公开发布结果。本文从海气耦合机制和热量收支的角度对耦合模式结果和相应的大气模式比较计划试验(AMIP)进行了对比分析,探讨了造成这一地区海温和降水模拟偏差的原因。结果显示,新一代的模式g3和f3-L模拟的热带太平洋区域气候平均态有明显改进,模拟的海表温度均方根误差为1度左右,而上一代模式g2和s2均方根误差则在2度以上,相较而言误差降低了50%左右。但是新一代版本模拟的降水没有显著改进。从东太平洋赤道南北温度和降水的不对称性来看,f3-L模拟结果最好,因为该版本中赤道太平洋地区的净短波辐射平均态误差的减小,海洋上层热量动力输送过程的改善和净短波辐射与海温回归关系改进,赤道太平洋地区海温的平均态更加接近观测。另外,赤道北侧ITCZ的降水偏大4mm/day,比之前的模式更加严重。对流降水带来的凝结潜热释放加强了南北非绝热加热梯度,越赤道南风加强,风场的误差抵消了一部分因为净短波辐射偏大带来的海温偏暖,这说明海温平均态的改善部分是模拟误差相互抵消的结果。在季节循环的模拟方面也存在类似的现象,f3-L和g3中的海温年循环有所改进但较观测相比振幅仍旧偏弱。年循环有所改进是因为,f3-L和g3模拟的经向风和潜热的年循环振幅比前版本更要偏强,也就是说误差加大,但是却更大程度上抵消短波辐射的年循环偏差,使得模拟的赤道东太平洋SST年循环相对前一版本有明显改进。而g2和s2模拟的海温在赤道东太平洋则存在一个虚假半年循环分量,这主要是由潜热通量半年循环偏差所引起的。

    Abstract:

    In this study ,we evaluated the ability of four versions of Flexible Global Ocean-Atmosphere-Land System model (FGOALS) developed at State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics(LASG), Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences in simulating climatology and seasonal cycle of tropical pacific precipitation and SST.FGOALS-f3-L and FGAOLS-g3 participated the Coupled Model Intercomparison Project (CMIP) Phase 6 while FGOALS-s2,FGOALS-g2 participated the CMIP Phase 5 (CMIP5)).This paper compared historical and AMIP simulations in terms of atmosphere-ocean feedback mechanisms and heat budget analysis to investigate the formation of precipitation and SST biases. The results exhibited notable improvements in FGOALS-g3 and FGOALS-f3-L compared with the previous versions ,such as a reduction of 50% of RMSE of SST decreasing from above 2 °C in FGOALS-g2 and FGOALS-s2 to 1 °C in FGOALS-f3-L. However, there are negligible improvements in precipitation. FGOALS-f3-L reproduces the meridional asymmetry of SST and precipitation in East Pacific well because of the reduction of errors in the mean state of shortwave radiation and its reasonable representations of ocean dynamic heat transport and surface shortwave radiation feedback. Moreover, excessive rainfall biases in the northern side of the equator become more severe than previous models, which is greater than 4mm/day. This overestimated convections bring latent heat which enhances the latitudinal ?diabatic heating gradient and strengthen the cross equatorial south wind. Errors in wind actually cancel out part of the warm biases of SST resulting from overestimation of shortwave radiation. Similar error sources existed in the simulated seasonal cycle , characterized by an improved annual cycle but a weaker overall amplitude in FGOALS-g3 and FGOALS-f3-L.This improved annual signal of SST results from stronger amplitude of annual cycle of meridional wind and latent heat flux. Actually, errors of wind and latent heat are bigger but cancel out the annual biases in short wave radiation flux. Therefore, the annual signal in SST seems to be enhanced than former versions. While the false semi-annual cycle of SST in FGOALS-g2 and FGOALS-s2 is mostly result from the semi-annual cycle of latent heat flux.

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  • 收稿日期:2021-03-03
  • 最后修改日期:2021-05-10
  • 录用日期:2021-05-14
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