高频活动对MJO东移影响的观测和模拟研究

The Madden-Julian Oscillation (MJO) is the most prominent mode of intraseasonal variability in the tropics, and it is also the most important predictability source of extended-range of weather forecasting. Understanding the mechanism for eastward propagation of the MJO has great importance for both science and society. Previous studies have shown that the upscale feedback associated with high-frequency disturbances plays an important role in the propagation of MJO, but the results have large uncertainties. This proposal aims to use both the latest reanalysis dataset with high space-time resolution (ERA-Interim) plus the latest multi-model results derived from the multi-model comparison project developed by the Working Group on Numerical Experimentation MJO Task Force (MJOTF) and the GEWEX Atmospheric System Study (GASS), and conduct numerical experiments to investigate the characteristics of synoptic-scale activity associated with the eastward propagating MJO as well as its impact on the propagation of MJO. The main tasks in this proposal consist of 1) making an analysis of phase relationship between high-frequency disturbances and the MJO convection over the tropics; 2) making a quantitatively diagnosis of the contribution from nonlinear advection terms to the east-west asymmetric distributions of moisture relative to the MJO convection, so that to understand the upscale feedback from high-frequency activity to MJO propagation; and 3) revealing the relationship between the simulation skills of high-frequency disturbances and the eastward propagation of intraseasonal signals by using multi-model results, to understand to what extent the high-frequency activities contribute to the propagation of MJO in the model world. The merit of this project is to advance the understanding of tropical climate dynamics, which may further benefit the development and improvement of model physics on MJO simulation and prediction.

季节内振荡（MJO）为热带大气次季节尺度上最主要的模态，也是延伸期预报中最重要的可预报性来源。理解MJO的传播机制具有重要的科学意义和现实意义。高频天气尺度活动的升尺度反馈作用在MJO东移过程中扮演重要角色，但已有研究成果仍具有不确定性。本项目拟利用高时空分辨率的再分资料（ERA-Interim）以及最新的多模式资料（MJOTF/GASS）进行分析诊断并结合数值试验，揭示MJO对应的天气尺度活动特征并研究高频活动对MJO传播的影响。包含以下内容：1）分析大气高频活动与MJO对流的位相配置关系；2）定量诊断高频活动引起的非线性平流对于水汽东-西不对称分布的相对贡献，阐明高频活动对MJO移动的升尺度反馈作用；3）分析多模式结果中高频活动与季节内振荡信号东移的对应关系，揭示模式中高频活动对于MJO传播的重要性。项目研究成果将提升对热带气候动力过程的理解，并为改进模式模拟和预报MJO提供依据。

季节内振荡(MJO)为热带大气次季节尺度上最主要的模态，也是延伸期预报中最重要的可预报性来源。然而现有的线型理论无法完美的解释观测中MJO的东传现象，且当前的动力模式对MJO传播的模拟能力也十分有限。已有研究表明高频天气尺度活动引起的非线性过程会对MJO产生升尺度反馈，在MJO东移过程中扮演重要角色，但已有研究成果仍具有不确定性。..本项目从观测资料诊断和数值试验两方面，系统考察了MJO传播与大气高频活动之间的双向关系，定量诊断了高频活动对MJO对流传播的贡献，研究了不同种类高频扰动在MJO传播中所起起的作用，评估了数值模式对MJO与高频活动之间关系的模拟能力。研究结果揭示了MJO对流通过影响正压能量转换对高频活动的调制作用，明确了高频活动引起的水汽非线性平流对MJO对流东移的定量贡献，指出赤道罗斯贝波和开尔文波均对MJO对流东移起正的贡献作用，揭示出当前CMIP6耦合模式对高频活动的模拟偏差。..研究结果加深了对热带多尺度相互作用过程的理解，为改进模式模拟和预报MJO提供依据，从而有益于提高延伸期尺度上的天气预报能力。