Analysis on the Dynamics of a Wave-like Teleconnection Pattern along the Summertime Asian Jet Based on a Reanalysis Dataset and Climate Model Simulations
Analysis on the Dynamics of a Wave-like Teleconnection Pattern along the Summertime Asian Jet Based on a Reanalysis Dataset and Climate Model Simulations
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DOI：
10.2151/jmsj.87.561
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发表时间：
2009-06-01
影响因子：
3.1
通讯作者：
Kimoto, Masahide
中科院分区：
文献类型：
--
作者：
Kosaka, Yu;Nakamura, Hisashi;Kimoto, Masahide
丝绸之路型是影响东亚夏季气候的主要遥相关型之一，它是沿夏季亚洲急流观测到的一种波浪型距平型。我们基于再分析(JRA-25)数据集的分析证实了传统的观点，即这种模式具有自由定常Rossby波列的特征，其水平波数接近于由急流平均强度确定的定常Rossby波数。然而，我们的分析揭示了它作为一种动力模式的更本质的特征，从斜压亚洲急流中提取可用势能对于其自我维持是非常有效的。我们的分析还揭示了它的正压能量转换对亚洲急流细微的纬向不对称性的高度敏感性，这可以被认为是将最强涡度异常固定在西风急流核心周围，从而确定观测到的波列的最佳纵向位相排列的关键因素。事实上，对一个全球斜压模式的奇异值分解导致了在结构和能量方面类似于丝绸之路模式的扰动的识别。结果表明，平均气流的形态决定了丝绸之路模式的主导位相、经向位置和波数。上述丝绸之路模式的动力学特征被发现有助于评估和解释参与耦合模式国际比较项目(CMIP3)第三阶段的气候模型模拟的现代气候中丝绸之路模式的重复性。这种模式倾向于被确定为对流层上层经向风变率的主导模式，这类模式可以真实地再现平均亚洲急流，包括其纬向结构，这证实了我们的观测分析中揭示的丝绸之路模式的动力学。在我们分析的基础上，提出了一个衡量模型模式重现性的指标。
The Silk Road pattern, a wave-like anomaly pattern observed along the summertime Asian jet, is one of the major teleconnection patterns that can influence the East Asian summertime climate. Our analysis based on a reanalysis (JRA-25) dataset confirms the conventional notion that the pattern has a characteristic of a free stationary Rossby wave train, with its horizontal wavenumber close to the stationary Rossby wavenumber determined by the mean intensity of the jet. However, our analysis reveals its more essential characteristic as a dynamical mode whose extraction of available potential energy from the baroclinic Asian jet is highly efficient for its self-maintenance. Our analysis also reveals high sensitivity of its barotropic energy conversion to subtle zonal asymmetries of the Asian jet, which call be regarded as a critical factor to anchor the strongest vorticity anomaly around the western jet core and thereby determine the preferred longitudinal phase alignment of the wave train as observed. In fact, singular value decomposition of a global baroclinic model linearized about the observed mean state for boreal summer leads to identification of a perturbation similar to the Silk Road pattern with respect to its structure and energetics. It is thus indicated that the configuration of the mean flow determines the dominant phase, as well as the meridional location and the wavenumber, of the Silk Road pattern.The aforementioned dynamical characteristics of the Silk Road pattern are found useful for assessing and interpreting the reproducibility of the pattern in the present-day climate simulated in climate models that participated in the phase 3 of the Coupled Model Intercomparison Project (CMIP3). The pattern tends to be identified as the dominant mode of upper-tropospheric meridional wind variability as observed in such models that can reproduce the mean Asian jet realistically, including its zonal structure, which confirms the dynamics of the Silk Road pattern revealed in our observational analysis. Oil the basis of our analysis, a metric is proposed for assessing the models' reproducibility of the pattern.