IAP AGCM4.0模式对热带大气季节内振荡的模拟评估

基于中国科学院大气物理所大气环流模式IAP AGCM4.0总共30年(1979~2008年)的模拟结果,评估了IAP AGCM4.0模式对热带大气季节内振荡的模拟能力。分析结果表明IAP AGCM4.0模式可以在一定程度上模拟出热带大气季节内振荡的主要时空谱结构特征,在周期30~80天处存在明显的谱能量中心;模式模拟的季节内振荡东传的主要特征与观测基本一致,东移波的能量远大于西移波。基于RMM指数(All-season Real-time Multivariate MJO Index)的分析表明,模式模拟的850 h Pa和200 h Pa季节内尺度风场和对流活动在赤道地区的空间分布与观测基本一致。但与观测相比,模式模拟的热带大气季节内振荡的周期较短,东传速度快于观测,虚假的西传特征过强,对流活跃区域范围较小、强度较弱。就非绝热加热而言,模式模拟结果与再分析资料比较接近,但最大加热在印度洋和西太平洋地区出现的位相较晚。进一步分析表明,模式中影响对流触发的相对湿度阈值(RHc)的不同取值(RHc分别取为85%、90%、95%和100%),可以显著影响热带大气非绝热加热垂直廓线,从而影响模式对热带大气季节内振荡的模拟;当对流触发相对湿度阈值取为90%时,IAP AGCM4.0模式对热带大气季节内振荡模拟的能力相对最好,非绝热加热垂直廓线在不同位相的分布特征也与再分析资料最为接近。这说明模式对流参数化方案中不同参数的合适选取,可以改进模式对热带大气季节内振荡的模拟能力。

The Madden-Julian Oscillation Simulated by the IAP AGCM4.0

The performance of IAP (Institute of Atmospheric Physics) Atmospheric General Circulation Model Version 4.0 (IAP AGCM4.0) in simulating the Madden-Julian Oscillation (MJO) is examined in this paper using the 30-year model integration results during 1979-2008. It is found that the IAP AGCM4.0 can reproduce the observed wave number-frequency power spectrum of MJO to some extent, with dominant spectrum power at wavenumber 1 and periods of 30-80 days. Meanwhile, the IAP AGCM4.0 can generally reproduce the observed coherent eastward propagating signals at the intraseasonal time scale, with the power of eastward moving waves much stronger than that of the westward moving waves. The RMM (Real-time Multivariate MJO) index is further applied to evaluate the simulated MJO structure. It is found that IAP AGCM4.0 can well reproduce the observed intraseasonal signals of 850 hPa and 200 hPa zonal winds and the enhanced convection structure of MJO in the tropical regions. However, the simulated eastward propagation is generally too fast, and the simulated westward propagation is stronger than the observation. IAP AGCM4.0 also splits the intraseasonal convective anomalies into two centers straddling the equator, and produces weaker convection. The vertical profile of diabatic heating simulated by the IAP AGCM4.0 has a similar structure to the observation, but in the Indian Ocean and western Pacific Ocean, positive maximum heating occurs later than the observation in phases. Numerical experiments are conducted by using different RHc (relative humidity criterion) values of 85%, 90%, 95%, and 100% for triggering the convection. It is found that the vertical diabatic heating profiles for experiments with different RHc vary considerably, which can lead to differences in the simulated MJO features. Comparison of results further shows that both the main features of MJO and vertical diabatic heating profiles are best simulated when RHc is set to 90%. This suggests that proper specifications of the values for key parameters in the convective parameterization scheme might help improve the model capability in simulating the observed features of MJO.