FORMATION MECHANISM OF STORM TRACKS AND THEIR FEEDBACK EFFECTS TO THE TIME-MEAN CIRCULATION

在北半球冬季环流中，在温带对流层中天气尺度扰动活动增强的风暴路径纬向定位于太平洋和大西洋上空。然而，风暴路径纬向定位的动力机制尚未完全确定。它们对时间平均对流层环流形成的作用也存在争议。特别是，对于理解年代际气候变率动力学至关重要的温带海表温度（SST）分布与风暴路径形成的相关性尚不清楚。本文通过对大气环流模式（AGCM） （CCSR/NIES AGCM，水平分辨率为42，垂直分辨率为20）的一系列长期整合，揭示了风暴路径的动力学及其对时间平均环流的反馈。数值实验是在没有地形的永久一月条件下进行的，指定了理想的海陆和海温分布。结果表明：1在没有地形强迫罗斯比波的情况下，下层海温分布形成的低空斜压的纬向不对称对风暴局域化是不可或缺的，而对流层上层环流中的副热带急流和正压能量转换等纬向不对称对风暴局域化仅起次要作用低层斜压性的纬向不对称是由与风暴路径相关的非绝热加热分布所强迫的静止行星波维持的因此，天气尺度涡旋与行星波之间通过非绝热加热的正反馈机制对纬向风暴路径的局域化起着最重要的作用。

In the wintertime northern hemispheric circulations, storm tracks where the activity of synoptic-scale disturbances is enhanced in the extratropical troposphere are zonally localized over the Pacific and the Atlantic. However, the dynamical mechanism of the zonally localization of storm tracks has not been fully established. Their role on the formation of the time-mean tropospheric circulation is also controversial. In particular, the relevance of extratropical sea surface temperature (SST) distribution to the storm track formation, which is central to understand the dynamics of decadal climate variability remains unclear. In this study, we proceeded a series of long-term integration of an atmospheric general circulation model (AGCM) (CCSR/NIES AGCM with horizontal resolution of T42 and 20 vertical levels) to reveal the dynamics of storm track and its feedback onto the time-mean circulation. The numerical experiments were conducted under a perpetual January condition without topography by specifying idealized land-sea and SST distribution. The following results were obtained:1 In the absence of topographically forced Rossby waves, the zonal asymmetry of the low-level baroclinicity formed by the underlying SST distribution is indispensable to localize the storm, while that in the upper tropospheric circulation, such as subtropical jet and barotropic energy conversion, plays only a secondary role.2 The zonal asymmetry of the low-level baroclinicity is maintained by stationary planetary waves forced by the diabatic heating distribution associated with the storm track.3 Thus, the positive feedback mechanism between synoptic-scale eddies and planetary waves through the diabatic heating plays the most important role in localizing the storm track in the zonal direction.