Development of a Three-Dimensional Spectral Linear Baroclinic Model and its Application to the Baroclinic Instability Associated with Positive and Negative Arctic Oscillation Indices
Development of a Three-Dimensional Spectral Linear Baroclinic Model and its Application to the Baroclinic Instability Associated with Positive and Negative Arctic Oscillation Indices
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DOI：
10.2151/jmsj.2013-207
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发表时间：
2013-04
影响因子：
3.1
通讯作者：
H. Tanaka;Sawaka Seki
中科院分区：
文献类型：
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作者：
H. Tanaka;Sawaka Seki
本文从三维谱原方程模型出发，建立了线性斜压模型。利用这一LBM，研究了球面上各种纬变基本态的线性稳定性问题。对于纬向气候基本态，我们证实传统的Charney模态和偶极子Charney模态在天气尺度到行星尺度上是最主要的不稳定模态。对于纬向变化的基本态，我们发现这些不稳定模态受到基本态局部斜压性的区域性的修正。考虑到纬向变化的正压基本态，我们发现最不稳定的正压模式是北极涛动（AO）模式。在本研究中，LBM的特征解被视为静止大气下三维正态向任意气候基本态的广义扩展。作为LBM的一种应用，将与AO正指数和负指数相关的各种纬向变化的基本态代入LBM中，以求斜压涡的响应。结果表明，由于双喷流结构的增强，大西洋扇区正反馈主导了正AO指数。当AO指数为负时，由于斜压不稳定性增强，大西洋和太平洋扇区的副热带急流在中纬度地区辐合，向极地移动。在大西洋和太平洋扇区，正反馈以不同的方式运作，这取决于它们的双或单西风喷气机。结果表明，正/负AO指数对临床压不稳定模态进行了修正，使诱发的局部涡动量通量对AO呈正反馈。
In this study, a linear baroclinic model (LBM) is developed from a three-dimensional (3D) spectral primitive equation model. With this LBM, we investigate the linear stability problem for various zonally varying basic states on a sphere. For a zonal climate basic state, we confirm that the traditional Charney and dipole Charney modes appear as the most dominant unstable modes in the synoptic to planetary scales. For a zonally varying basic state, we find that these unstable modes are modified by the regionality of the local baroclinicity of the basic state. Given the zonally varying barotropic basic state, we find that the barotropically most unstable standing mode appears to be the Arctic Oscillation (AO)mode. In this study, the eigensolution of the LBM is regarded as a generalized extension at the 3D normal mode at the motionless atmosphere to those of an arbitrary climate basic state. As an application of the LBM, various zonally varying basic states associated with the positive and negative AO indices are substituted into the LBM to find the response of the baroclinic eddies. According to the result, the positive feedback dominates in the Atlantic sector for positive AO index because of the presence of enhanced double-jet structure. When the AO index is negative, the eddy momentum flux converges in the mid-latitudes to shift the subtropical jet poleward in the Atlantic and Pacific sectors because of the intensified baroclinic instability. The positive feedback operates in a different way in the Atlantic and Pacific sectors depending on their double or single westerly jets. It is concluded that the baroclinically unstable modes are modified by the positive/negative AO index, so that the induced local eddy momentum flux shows a positive feedback to the AO.