CMIP5模式对东亚冬季风指数变化及其与冬季大气环流和气温关系的模拟评估

本文评估了44个CMIP5模式对东亚冬季风环流系统,特别是东亚冬季风指数及其对应的环流和气温特征的模拟能力.结果表明:CMIP5模式对地表气温和500 hPa位势高度场模拟效果最好,对200 hPa纬向风的模拟次之,而对海平面气压和850 hPa经向风的模拟相对较差.与单个模式相比,多模式集合(MME)的模拟能力要更优,其能够很好地再现西伯利亚高压、阿留申低压、东亚低层偏北风、中层东亚大槽、高层东亚西风急流以及地表气温的空间分布.不过,模拟的环流系统偏强,造成东亚地表气温总体偏低.对于东亚冬季风指数,分别选取基于300 hPa纬向风(I_(Jhun))、850 hPa风场(I_(Wang))、500 hPa位势高度(I_(Cui))、以及海平面气压(I_(Guo))定义的四个指数表征东亚冬季风强度.MME能很好地模拟I_(Cui)和I_(Wang)指数的长期变化,还能合理再现四个指数所指示的东亚冬季风环流和气温的变化特征:对应冬季风偏强年份,西伯利亚高压、阿留申低压、东亚沿岸低层北风、东亚大槽和高空西风急流加强,东亚大陆地表气温和极端低温降低,但变化的幅度比观测结果偏弱.

Evaluation of the CMIP5 models in simulating the change of the East Asian winter monsoon indices and their relationship with the wintertime atmospheric circulation and temperature

Based on the simulations of 44 models archived in the Coupled Model Intercomparison Project phase 5 (CMIP5), this study evaluated their performance in modeling the East Asian winter monsoon (EAWM) and associated atmospheric circulation and temperature. The results show that the CMIP5 models have the best capacity to simulate the surface air temperature and the 500 hPa geopotential height, followed by the 200 hPa zonal wind and then the sea level pressure and the 850 hPa meridional wind. Moreover, the multimodel ensemble (MME), which outperforms the individual model, can well capture the spatial distribution of the Siberian high, the Aleutian low, the prevailing northerly wind over East Asia in the lower troposphere, the East Asian major trough in the middle troposphere, and the East Asian jet stream in the upper troposphere as well as the surface air temperature. However, the simulated circulation system is generally stronger than the observation, leading to a general cold bias of the East Asian surface air temperature. Further, four indices named I_Jhun, I_Wang, I_Cui and I_Guo that were defined respectively from 300 hPa zonal winds, from 850 hPa winds, from 500 hPa geopotential height, and from sea level pressure were selected to represent the EAWM intensity. The MME can successfully reproduce the secular change of the ICui and IWang. The features of the anomalies in atmospheric circulation and temperature related to the four indices can also be reproduced reasonably. That is, a strong EAWM corresponds to a strengthening of the Siberian high, the Aleutian low, the East Asian major trough and the East Asian westerly jet stream and an intensification of the northerlies prevailing over East Asia in the lower troposphere, consequently resulting in a decrease in surface air temperature and extreme low temperature over East Asia. Nevertheless, the amplitude of the change in the simulations is weaker than that in the observation.