热带大气季节内振荡数值模拟对积云对流参数化方案的敏感性

SENSITIVITY OF NUMERICALLY SIMULATED TROPICAL INTRA-SEASONAL OSCILLATIONS TO CUMULUS SCHEMES

利用中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)的大气环流模式(SAMIL-R42L9)研究了热带大气季节内振荡(MJO)的模拟对积云对流参数化方案的敏感性,结果表明两种对流参数化方案——湿对流调整方案(MCA)和Zhang-McFarlane(1995年)方案对MJO的模拟能力有明显的差异。MCA方案较好地模拟出了MJO的基本特征,包括季节内的时间尺度和向东的传播。Zhang-McFarlane(1995年)对流方案模拟的MJO振幅非常弱,而且缺乏连续的传播特征,在MJO的演变过程中弱的低层水汽辐合使MJO难以维持和传播。两种不同的对流参数化方案产生的非绝热加热垂直廓线明显不同,Zhang-McFarlane(1995年)方案产生的非绝热加热强度在对流层各层过于一致,没有明显的最大加热层,而且平均的加热强度太弱,这是该方案难以模拟出合理的MJO的主要原因之一。因此,模式对热带大气季节内振荡的模拟能力很大程度上依赖于所使用的积云对流参数化方案,当积云参数化方案改变时模式模拟的MJO也发生明显变化,而非绝热加热廓线是对流参数化方案影响MJO模拟的一个重要影响因子。3种不同的非绝热加热垂直分布的敏感性试验表明,当最大的加热层位于对流层中低层尤其是对流层中层时,更容易产生出与观测较为接近的季节内的扰动,而当最大加热位于对流层高层时,更易于激发出西传的扰动。

The sensitivity of the simulated MJO to different cumulus parameterization schemes employed is studied by using the atmosphere general circulation model-SAMIL-R42L9 developed by the Laboratory for Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG） in the Institute of Atmospheric Physics （IAP） of Chinese Academy Sciences. Results show clearly that the performance of the model in simulating the MJO changed widely when using two different cumulus parameterization schemes the moist convective adjustment scheme （MCA） and the Zhang-McFarlane scheme, respectively. The MJO simulated by the MCA scheme was found to be more realistic than that by the Zhang-McFarlane scheme including the intraseasonal timescales and eastward propagation. The MJO produced by the Zhang-McFarlane scheme was too weak and showed little propagation characteristics. The weak moisture convergence at the low level simulated by the Zhang-McFarlane scheme is not strong enough to maintain the structure and the eastward propagation of the oscillation. This two cumulus schemes produced different vertical structures of the heating profiles. The heating profile in the Zhang-McFarlane scheme is nearly uniform with height and the heating strength is too weak compared to that produced by the MCA scheme, which maybe contributes greatly to the failure of simulating reasonable MJO. Comparing simulated MJOs by the two schemes indicate that the intraseasonal oscillations simulated by the general circulation model are highly sensitive to cumulus parameterization schemes employed. The performance of the general circulation model in simulating MJO can change widely when the cumulus parameterization scheme is changed. For different cumulus parameterization schemes, the diabatic heating profiles produced by them plays important role on the performance of the GCM. In order to argue further the impacts of the diabatic heating profiles on the MJO simulation, three sensitive experiments with different heating profiles were designed in which modified heating profiles respectively peak in the upper （UH）, middle （MH）, and lower troposphere （LH）. Both the LH run and MH run produced eastward propagating signals at the intraseasonal timescales, while it is interesting to note that the intraseasonal timescales signals produced by the UH run propagated westward. This indicates that realistic intraseasonal oscillation is more prone to be excited when the maximum heating concentrates in the middle-low level, especially in middle level, while, westward propagating disturbances on the intraseasonal time scales are more prone to be produced when the height of the maximum heating is too high.