Miyakawa Tomoki, Kikuchi Kazuyoshi
Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
International Pacific Research Center, University of Hawaii, Honolulu, USA.
Sci Rep. 2018 Aug 3;8(1):11664. doi: 10.1038/s41598-018-29931-4.
The role of tropical atmospheric waves in the propagation mechanism of the Madden-Julian oscillation (MJO), a huge eastward-propagating atmospheric pulse that dominates intraseasonal variation of the tropics and affects the entire globe, has been long discussed but remains unclear. An MJO event observed in a major field campaign is reproduced using a front-running global cloud/cloud-system resolving model with 3.5 km, 7 km, and 14 km meshes. The eastward-migration speed of the MJO convective envelope in the 3.5 km and 14 km simulations agree well with observation, despite weak Kelvin wave signal power calculated by applying a combined Fourier-wavelet transform method. Our results suggest that the eastward propagation of this MJO event was principally controlled by an MJO-scale energy balance, and not by dynamical interaction of embedded tropical waves. The eastward propagation is delayed in the 7 km simulation, which features the highest surface latent heat flux to the west of the convective envelope center. This latent heat flux appears to be caused by prolonged existence of westward-migrating Rossby wave-like cyclonic disturbances near the equator; the embedded waves may not be part of the essential mechanism for the MJO eastward propagation, but can affect it by altering the energy balance.
热带大气波动在马登-朱利安振荡（MJO）的传播机制中所起的作用一直备受讨论，但仍不明确。MJO是一种巨大的向东传播的大气脉动，主导着热带地区的季节内变化并影响全球。利用一个具有3.5公里、7公里和14公里网格的前沿全球云/云系统解析模型，再现了在一次大型实地考察中观测到的一次MJO事件。在3.5公里和14公里模拟中，MJO对流包络的向东迁移速度与观测结果吻合良好，尽管通过应用联合傅里叶-小波变换方法计算出的开尔文波信号功率较弱。我们的结果表明，这次MJO事件的向东传播主要受MJO尺度的能量平衡控制，而非由嵌入的热带波动的动力相互作用控制。在7公里模拟中，向东传播出现延迟，该模拟中对流包络中心以西的地表潜热通量最高。这种潜热通量似乎是由赤道附近向西迁移的罗斯贝波状气旋扰动的长期存在引起的；嵌入的波动可能不是MJO向东传播基本机制的一部分，但可以通过改变能量平衡来影响它。
