双月刊

ISSN 1006-9895

CN 11-1768/O4

北非季风气候态及其年际变率的数值模拟:基于FGOALS-g3的诊断分析
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中国科学院大气物理研究所

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中国科学院“国际伙伴计划-国际大科学计划培育专项”项目“全球季风模拟研究国际计划”(资助号134111KYSB20160031)、第二次青藏科考项目 (STEP) (资助号2019QZKK0102)


Simulation of Climatology and Interannual Variability of North African Monsoon: An analysis based on FGOALS-g3
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Institute of Atmospheric Physics, Chinese Academy of Sciences

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    摘要:

    本文基于参加第六次“国际耦合模式比较计划”(CMIP6)的IAP/LASG 气候系统模式FGOALS-g3的耦合(Historical)与非耦合(AMIP)试验结果,通过与观测和再分析资料的比较,评估了FGOALS-g3模式Historical与AMIP试验对北非地区7-9月降水气候态和年际变率的模拟能力;利用水汽收支方程与回归分析研究了模式模拟降水偏差的原因;通过比较耦合与非耦合试验的模拟结果,分析了海气耦合过程对非洲季风模拟偏差的影响。结果表明,在气候平均态上,Historical与AMIP试验模拟的降水均较观测偏少且位置偏南,模拟的北非夏季西南季风环流偏弱。AMIP试验模拟的萨赫勒和北非季风区降水与观测降水的空间相关系数分别为0.80、0.62,均大于Historical试验,对应的均方根误差为2.58、3.23,小于Historical试验,说明与Historical试验相比,AMIP试验的模拟偏差更小。水汽收支分析表明,Historical与AMIP试验均低估了北非季风区水汽辐合,同时低估了水汽垂直平流项与蒸发项,高估了水平水汽平流项,导致模式模拟的降水偏少,且Historical试验的偏差大于AMIP试验。在年际变率方面,观测中,北非夏季风降水-ENSO呈负相关关系。AMIP试验能够模拟出ENSO正位相时北非夏季降水的负异常,且较观测负异常偏强,而Historical试验模拟的负相关关系并不显著。AMIP试验高估了北非地区垂直运动、热带东风急流与低层季风环流对ENSO的响应强度,导致降水异常偏强,而Historical试验低估了上述响应强度,产生弱降水负异常。水汽收支表明,北非夏季降水-ENSO的负相关关系由垂直水汽平流项异常引起,其中垂直动力项异常主导。AMIP试验高估了垂直平流项及其动力项的贡献,但Historical试验高估水平平流项与垂直热力项异常的贡献,说明Historical试验模拟的北非夏季降水-ENSO相关关系偏差与水平平流项异常的抑制作用有关。

    Abstract:

    Based on the comparison with observation and reanalysis data, the study evaluated the performance of the Atmospheric Model Intercomparison Project (AMIP) and the Coupled Model Intercomparison Project (CMIP) historical experiments of IAP/LASG climate system model FGOALS-g3 in simulating climatology and interannual variability of JAS (July–August–September) seasonal-mean North Africa Summer Monsoon (NASM) and Sahel precipitation, and explained the bias by moisture budget and regression analysis, investigating the influence of ocean-atmosphere coupling by comparing AMIP and Historical. The results showed that both Historical and AMIP experiments underestimated precipitation, simulating weaker south west monsoon winds and a further south rainfall position. The pattern correlation coefficients of precipitation in Sahel and North Africa monsoon region simulated by AMIP are 0.80 and 0.62, respectively, which are larger than those of Historical, and the corresponding root mean square errors are 2.58 and 3.23, which are smaller than those of historical experiment, indicating that the deviation of AMIP is smaller than that of Historical. Considering the moisture budget diagnosis, Historical and AMIP both underestimated the water vapor convergence over NASM region, estimating less vertical moisture advection and evaporation and more horizontal moisture advection than observation, which led to dry biases. In terms of interannual variability, the observation shows that North Africa summer monsoon rainfall is negatively correlated with ENSO. AMIP can reproduce the ENSO-NASM negative relationship, which is stronger than observation. However, Historical cannot reasonably simulate the relationship at interannual time scale. AMIP overestimates the circulation response of ENSO, including descending anomalies, weakened tropical easterly jet and decreased low-level monsoon over North Africa, which contributes to the stronger precipitation negative anomaly. In contrast, Historical underestimates the above ENSO-related response, resulting in feeble precipitation negative anomaly. Moisture budget analysis indicated that vertical moisture advection anomalies, especially the dynamic term of vertical moisture advection anomalies, dominated the ENSO-NASM negative relationship. AMIP is coincided with observation, but it overestimates the above term, which leads to stronger negative rainfall anomalies. While Historical overestimates horizontal advection and vertical thermodynamic anomalies, which indicates that horizontal advection anomalies cause the inhibited simulation of ENSO-NASM negative relationship.

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  • 收稿日期:2021-08-03
  • 最后修改日期:2021-11-23
  • 录用日期:2021-12-07
  • 在线发布日期: 2022-01-05
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