Madden-Julian振荡（MJO）的传播机制一直是MJO研究的重点。探寻影响MJO传播速度的因子有助于揭示MJO向东传播的物理本质。我院青年教师陈国森和夏威夷大学王斌教授研究了影响MJO传播速度的环流因子，相关研究成果近期在《Journal of Climate》上发表。

利用Hough函数分解，研究发现MJO的传播速度受其Kelvin波分量影响，而与其对流强度无关。Kelvin波分量越强，MJO传播速度越快。强的Kelvin波分量增强了MJO对流东侧的水汽条件和对流不稳定度，从而加速了MJO对流的向东传播。进一步研究表明，Kelvin波分量的强弱与赤道中太平洋的背景场海温存在正相关关系。当赤道中太平洋的背景场海温升高时，印度-太平洋暖池的纬向尺度增大，从而导致MJO的纬向尺度增大，进而有利于Kelvin波分量的增强。利用作者开发的理论模型，验证了暖池的纬向尺度对Kelvin波分量强度的影响。

该研究成果不仅进一步揭示了MJO传播的物理本质，也为预报MJO的传播速度提供了潜在预报因子。同时，该成果进一步从观测上验证了作者的MJO水汽动力模态理论。

图1. The MJO propagation speed (in unit of m s−1) against the (a) Kelvin wave index (in unit of m), (b) Rossby wave index (in unit of m s−1), (c) zonal scale index (number of grid point), and (d) convection amplitude index (in unit of W m−2). The linear correlation coefficients and the P values are shown. The red (blue) dots denote the slow (fast) MJO events, and the green dots denote the MJO events with propagation speed in between the fast and slow events.

图2. Observed background SST variation with MJO speed. Shown are the background SST anomalies (in unit of K m−1 s) regressed onto the MJO propagation speed. The stippled region indicates where the regressed background SST anomalies are significant at 95% confidence level. The background SST anomalies for an MJO event are defined as 3-month average of monthly SST anomalies (departure from climatological monthly mean), with the central month containing the day 0 of that MJO event.

图3. Model test of the warm pool effect. The Hovmöller diagrams of the equatorial (5°S–5°N averaged) precipitation anomalies (shading in unit of mm day−1) are shown for the (a) wide warm-pool simulation and (b) normal warm-pool simulation. (c),(d) The corresponding horizontal patterns of precipitation anomalies (shading in unit of mm day−1) and low-level geopotential height anomalies (contour with interval of 0.4 m) on day 130. The solid blue lines in (a) and (b) are least squares fits of the precipitation maximum.

相关文章：

Chen, G., and B. Wang, 2020: Circulation Factors Determining the Propagation Speed of the Madden–Julian Oscillation. Journal of Climate, 33, 3367-3380.

Chen, G., and B. Wang, 2019: Dynamic moisture mode versus moisture mode in MJO dynamics: importance of the wave feedback and boundary layer convergence feedback. Climate Dynamics, 52, 5127-5143.