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赵维佳, 陈国森. 2024. CMIP6模式对热带大气季节内振荡东传速度的模拟[J]. 大气科学, 48(2): 1−11. doi: 10.3878/j.issn.1006-9895.2211.22099
引用本文: 赵维佳, 陈国森. 2024. CMIP6模式对热带大气季节内振荡东传速度的模拟[J]. 大气科学, 48(2): 1−11. doi: 10.3878/j.issn.1006-9895.2211.22099
ZHAO Weijia, CHEN Guosen. 2024. Madden–Julian Oscillation Propagation Speed Simulated in CMIP6 Models [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 48(2): 1−11. doi: 10.3878/j.issn.1006-9895.2211.22099
Citation: ZHAO Weijia, CHEN Guosen. 2024. Madden–Julian Oscillation Propagation Speed Simulated in CMIP6 Models [J]. Chinese Journal of Atmospheric Sciences (in Chinese), 48(2): 1−11. doi: 10.3878/j.issn.1006-9895.2211.22099

CMIP6模式对热带大气季节内振荡东传速度的模拟

Madden–Julian Oscillation Propagation Speed Simulated in CMIP6 Models

  • 摘要: 成功预测热带大气季节内振荡(MJO)能够有效改进延伸期预报。但是目前对MJO的数值模拟仍具有一定的难度,其中一个主要挑战就是能否合理地模拟出MJO的传播速度。本文研究了CMIP6模式对MJO传播速度的模拟,并揭示了影响模式中MJO传播速度的因子。结果表明大部分CMIP6模式能够模拟出MJO在印度—太平洋暖池区域的传播特征,但对其平均传播速度的模拟存在显著的模式间差异。MJO的Kelvin波响应和Rossby波响应强度是影响模式中MJO传播速度的主要环流因子,强的Kelvin波响应有利于MJO加速东传,但强的Rossby波响应不利于MJO向东传播。模式间背景场海表温度(SST)的差异是导致Kelvin波响应差异的主要原因。MJO东传更快的模式在赤道太平洋中部和西北太平洋具有更高的SST。赤道太平洋中部偏暖主要以两种方式影响MJO的东传速度:第一,通过增加暖池的水平尺度,从而扩展MJO水平尺度,进而加强Kelvin波响应使得MJO东传加快;第二,通过增强该区域的水汽含量,减弱西太平洋纬向水汽梯度,导致纬向水汽平流增强,从而加速MJO东传。与前人研究不同,本研究发现西北太平洋增暖有助于加速模式中MJO的向东传播。西北太平洋增暖导致海温分布关于赤道更加对称,能够通过增强海洋性大陆北侧的水汽,使得背景场水汽分布关于赤道更加对称,从而有利于Kelvin波响应的发展。本研究的结论不仅能够提高我们对MJO传播动力机制的理解,也表明提高模式对背景场的模拟有助于改进对MJO传播特征的模拟。

     

    Abstract: Faithful simulation of the Madden–Julian oscillation (MJO) can significantly improve extended-range prediction, but numerical models have difficulty in simulating the MJO. A primary challenge is simulating the MJO propagation speed optimally. In this study, we examine the propagation speed of MJO during boreal winter in CMIP6 models and reveal the key factors controlling the MJO propagation speed in these models. The result shows that most of the CMIP6 models can well simulate the MJO’s eastward propagation over the Indo-Pacific warm pool, but the simulated MJOs in different models have diverse propagation speeds. Evidently, the Kelvin- and Rossby-wave responses to MJO heating are the key circulation factors affecting the simulated MJO propagation speed, with stronger Kelvin-wave and weaker Rossby-wave responses corresponding to faster propagation. The variation in the MJO circulation structure among models is attributed to the diverse background sea surface temperature (SST). Models simulating faster MJO typically have a higher SST over the central Pacific (CP) and western North Pacific (WNP). Warming over CP affects the MJO speed in two ways. First, this zonal expansion of the warm pool can increase the horizontal scale of the MJO, leading to a stronger Kelvin-wave response that favors faster MJO propagation. Second, it increases the moisture content over the CP, which weakens the zonal moisture gradient over the West Pacific, resulting in the acceleration of the MJO by enhancing the zonal moisture advection. In contrast to previous studies, we find that the SST warming over WNP also affects the MJO speed. The SST warming over the WNP yields a more symmetrical SST distribution about the equator, which enhances the moisture content over the Maritime Continent, leading to a more equatorial symmetric distribution of the background-specific humidity during boreal winter. This symmetric distribution of moisture is conducive to the development of the Kelvin-wave response. The results of this study not only have implications for understanding MJO dynamics but also indicate that realistic simulation of MJO requires fidelity in the simulation of background states.

     

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