Analysis of the East Asian Subtropical Westerly Jet Simulated by CCSR/NIES/FRCGC Coupled Climate System Model
Analysis of the East Asian Subtropical Westerly Jet Simulated by CCSR/NIES/FRCGC Coupled Climate System Model
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DOI：
10.2151/jmsj.86.257
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发表时间：
2008-04
影响因子：
3.1
通讯作者：
Yaocun Zhang;M. Takahashi;Lanli Guo
中科院分区：
文献类型：
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作者：
Yaocun Zhang;M. Takahashi;Lanli Guo
通过分析2 0世纪耦合模式与NCEP/NCAR再分析模式的差异，考察了CCSR/NIES/FRCGC气候系统模式(MIROC_HIRES和MIROC_MEDRES)模拟对流层高层东亚副热带西风急流(EASWJ)的主要特征，重点评价了模式在再现平均EASWJ结构、季节演变、年际变化以及EASWJ季节演变、经向温度梯度与对流层高层非绝热加热之间的关系。耦合模式较好地模拟了对流层上层EASWJ的平均垂直和水平结构、季节演变以及EASWJ位置与经向温度梯度的对应关系。模式分辨率的提高可以改善对EASWJ结构、季节演变和年际变化的模拟。然而，与NCEP/NCAR再分析相比，两个耦合模式都高估了冬季的EASWJ强度，低估了夏季的急流强度。模式EASWJ强度的偏差与对流层经向温度梯度的偏差有关，与夏季地面感热通量和冬季对流凝结加热以及经向热量输送梯度有关。耦合模式较好地模拟了30°N-45°N非绝热加热的季节演变及其与西风急流的联系。然而，与再分析位置相比，模拟的夏季最大非绝热加热位置偏东，非绝热加热强度相对较弱，特别是在MIROC_HIRES，而MIROC_MEDRES模式在冬季130°E附近再现了相对较强的非绝热加热。研究表明，冬季西太平洋的凝结潜热、夏季青藏高原北侧的地面感热和经向热输送梯度决定了EASWJ的强度、位置、结构及其季节演变。因此，合理地再现经向热输送梯度和地面非绝热加热是改进MIROC模式模拟EASWJ的关键。
The major features of the East Asian subtropical westerly jet (EASWJ) in the upper troposphere simulated by the two versions of CCSR/NIES/FRCGC climate system model (MIROC_Hires and MIROC_Medres) are examined by analyzing the differences between the coupled model 20th century simulations and the NCEP/NCAR reanalysis, focusing on the evaluation of the model performances in reproducing the mean EASWJ structures, the seasonal evolution, interannual variability, and the relationship among the EASWJ seasonal evolution, the meridional temperature gradient and the diabatic heating in the upper troposphere. The mean EASWJ vertical and horizontal structures, the seasonal evolution, and the correspondence of the EASWJ location to the meridional temperature gradient in the upper troposphere are well simulated in the coupled models. The increase in model resolution can improve the simulation of the EASWJ structures, seasonal evolution and interannual variability. However, both coupled models overestimate the EASWJ intensity in winter, and underestimate the jet intensity in summer, relative to the NCEP/NCAR reanalysis. The biases in model EASWJ intensity are found to be associated with biases in meridional temperature gradients in the troposphere, and furthermore with the surface sensible heat flux in summer and convective condensation heating in winter as well as the meridional heat transport gradient. The coupled models simulate well the seasonal evolution of the diabatic heating averaged between 30°N-45°N, and its association with the westerly jet. However, the simulated maximum diabatic heating in summer is located eastward compared with the reanalyzed position, with a relatively weak diabatic heating intensity, especially in MIROC_Hires, while the MIROC_Medres model reproduces relatively strong diabatic heating near 130°E in winter. This study suggests that the condensation latent heating over the western Pacific in winter, the surface sensible heating over the northern side of the Tibetan Plateau in summer and the meridional heat transport gradient determine the EASWJ intensity, location and structure as well as its seasonal evolution. Thus the reasonable reproductions of the meridional heat transport gradient and the surface diabatic heating are the key points for improving the EASWJ simulation by the MIROC model.