两个大气环流模式SAMIL和BCC_AGCM对北半球冬季极涡振荡的模拟对比

Comparison of SAMIL and BCC_AGCM Simulations of the Polar Vortex Oscillation in the Northern Hemisphere Winter

基于与NCEP再分析资料的比较,本文利用大气环流模式SAMIL和北京气候中心大气环流模式BCC_AGCM的1950～1999年的AMIP试验模拟数据,对北半球冬季环流及平流层极涡振荡的模拟性能进行了评估分析。结果表明两个模式都可以再现北半球环流基本型以及环流振荡的主导模态。对冬季气候平均态的模拟,两个模式模拟的热带—热带外温度梯度均偏大,极夜急流偏强,极涡偏冷偏强;100～20hPa平均位势高度场谐波分析表明两个模式模拟的行星波偏弱;气候平均的10hPa极夜急流均存在1个月的季节漂移,200hPa副热带西风急流较NCEP偏弱。两个模式模拟的环流变化的主导模态均代表极涡振荡,SAMIL极涡振荡的强度大于BCC_AGCM,BCC_AGCM极涡振荡的频率要高于SAMIL。连续功率谱分析表明,NCEP资料中极涡振荡存在4.6个月的显著周期,相应地,SAMIL中为5.5个月的显著周期,BCC_AGCM中为4.8个月。NCEP资料中的极涡振荡主要发生在12～3月,SAMIL模拟的极涡振荡主要发生在2～3月,BCC_AGCM模拟的极涡振荡主要发生在2～4月。

By using AMIP simulation results for 1950-1999 from SAMIL and BCC_AGCM, the performance of the models in simulating the winter stratospheric circulation and polar vortex oscillation is assessed by comparing their results with the NCEP data. Both models can reproduce the general patterns of the winter climatology and the leading oscillation mode of the winter stratospheric circulation. However, the meridional temperature gradients between the tropics and the extratropics simulated by two models, as well as the polar vortex and polar jet, are much stronger on average than those in the NCEP data. Harmonic analysis of the winter climatology geopotential height from 100 hPa to 20 hPa indicates that planetary waves in both models are significantly weaker than in the NCEP data. A one-month seasonal drift exists in the seasonal evolution of the 10 hPa polar jet in both models compared with the NCEP data, and the simulated subtropical westerly jet at 200 hPa is weaker. The first empirical orthogonal function modes of the zonal-mean zonal wind anomalies from both models reflect oscillations in the intensity of the stratospheric polar vortex, whereas the occurrence of polar vortex oscillation events is more frequent in BCC_AGCM than in SAMIL. The dominant period of the polar vortex oscillation events is 5.5 months in SAMIL, 4.8 months in BCC AGCM, and 4.6 months in the NCEP data. Furthermore, polar vortex oscillation events occur mainly in February-March in SAMIL and in February-April in BCC_AGCM, whereas they occur from December to March in the NCEP data.