Structure and dynamics of the summertime Pacific-Japan teleconnection pattern
Structure and dynamics of the summertime Pacific-Japan teleconnection pattern
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DOI：
10.1256/qj.05.204
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发表时间：
2006-07-01
影响因子：
8.9
通讯作者：
Nakamura, H.
中科院分区：
文献类型：
--
作者：
Kosaka, Y.;Nakamura, H.
热带西太平洋对流活动以遥相关的形式影响北半球夏季东亚地区的温带环流，被称为“太平洋-日本(PJ)型”，但其结构和动力学尚未得到深入研究。本文对菲律宾东部观测到的32个月对流增强事件进行了综合分析。与PJ型相关的合成月平均涡度异常呈纬向拉长，高度向极地倾斜明显。这种结构与热带第一斜压模式和中纬度正压结构的组合有根本的不同，后者被广泛认为是PJ模式的概念模式。波活动通量只在对流层下部指向极地，表明Rossby波遥相关主要通过低层西南急流发生。西太平洋倾斜异常可以有效地获得对流层上下平均急流出口的动能和垂直切变急流存在时的有效位能。对流增强可以有效地产生APE，与之相关的低层异常环流增加了对流区的水汽供应，同时增强了预增温海洋表面的蒸发。因此，可以认为PJ型是一种动力模式，可以通过湿过程有效地激发与亚洲夏季风有关的纬向不对称斜压平均流，并具有有效的自持机制。
Convective activity over the tropical western Pacific is known to influence the extratropical circulation over East Asia in the boreal summer in the form of teleconnection, called the 'Pacific-Japan (PJ) pattern', but its structure and dynamics have not yet been studied in depth. In this study, a composite analysis is performed for 32 monthly events of enhanced convection observed to the east of the Philippines. The composited monthly mean vorticity anomalies associated with the PJ pattern are elongated zonally with a distinct poleward tilt with height. This structure differs fundamentally from a combination of the first baroclinic mode in the tropics and the barotropic structure in midlatitudes, as has widely been accepted as a conceptual model of the PJ pattern. A wave-activity flux points polewards only in the lower troposphere, indicating that Rossby wave teleconnection occurs primarily through a low-level south-westerly jet. Those tilted anomalies over the western Pacific can effectively gain kinetic energy in the exits of the mean jet streams in the upper and lower troposphere and available potential energy (APE) in the presence of the vertically sheared jets. The enhanced convection can generate APE effectively, and the associated low-level anomalous circulation acts to increase moisture supply into the convective region while enhancing evaporation from the pre-warmed ocean surface. It is thus hypothesized that the PJ pattern may be regarded as a dynamical mode that can be effectively excited in the zonally asymmetric baroclinic mean flow associated with the Asian summer monsoon with an efficient self-sustaining mechanism through moist processes.