Mechanisms of Meridional Teleconnection Observed between a Summer Monsoon System and a Subtropical Anticyclone. Part I: The Pacific-Japan Pattern
Mechanisms of Meridional Teleconnection Observed between a Summer Monsoon System and a Subtropical Anticyclone. Part I: The Pacific-Japan Pattern
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DOI：
10.1175/2010jcli3413.1
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发表时间：
2010-10-01
影响因子：
4.9
通讯作者：
Nakamura, Hisashi
中科院分区：
文献类型：
--
作者：
Kosaka, Yu;Nakamura, Hisashi
北太平洋西部中纬度地区夏季大气环流受到菲律宾附近异常对流活动的影响。这种经向遥相关在每月异常中观察到，被称为太平洋-日本（PJ）模式，其特征是在对流层下层增强对流中心周围及其东北部分别出现纬向拉长的气旋和反气旋异常，并随高度出现明显的极向相位倾斜。作者的理想化双层线性模型，其基本状态由纬向副热带急流和一对季风系统和副热带反气旋组成，可以模拟对位于这对之间的非绝热加热的类似 PJ 的响应。观察到的和模拟的每个模式都可以通过从带状变化的斜压平均流的正压和斜压转换来获得能量，其效率与异常非绝热加热产生的能量相当，表明该模式作为干动力模式的特征。事实上，转换效率对异常模式相对于气候平均流量的位置很敏感。此外，理想化模型中确定的第二最小阻尼模式与观察到的 PJ 模式具有一定的相似性，表明其模态特征以及这些特征在模式平均场中的至关重要性。除PJ模式外，观测发现另一种能量转换效率高的经向遥相关模式与小笠原群岛附近的异常对流有关。PJ模式的异常环流反过来又可以通过增强蒸发和水汽辐合以及动态诱发异常上升来加剧菲律宾附近的异常对流活动。因此，假设 PJ 模式可以被视为一种湿动力模式，它通过干能量转换和与湿过程的相互作用来维持自身。
Summertime atmospheric circulation over the midlatitude western North Pacific (WNP) is influenced by anomalous convective activity near the Philippines. This meridional teleconnection, observed in monthly anomalies and known as the Pacific-Japan (PJ) pattern, is characterized by zonally elongated cyclonic and anticyclonic anomalies around the enhanced convection center and to its northeast, respectively, in the lower troposphere, with an apparent poleward phase tilt with height. The authors' idealized two-layer linear model, whose basic state consists of a zonal subtropical jet and a pair of a monsoon system and a subtropical anticyclone, can simulate a PJ-like response against diabatic heating located between the pair. Each of the observed and simulated patterns can gain energy through barotropic and baroclinic conversions from the zonally varying baroclinic mean flow, in an efficiency comparable with that of energy generation due to the anomalous diabatic heating, indicating a characteristic of the pattern as a dry dynamical mode. In fact, the conversion efficiency is sensitive to the location of the anomaly pattern relative to the climatological-mean flow. Furthermore, the second-least damped mode identified in the idealized model bears certain resemblance with the observed PJ pattern, indicating its modal characteristics as well as a critical importance of these features in the mean field for the pattern. In addition to the PJ pattern, another meridional teleconnection pattern with high efficiency for its energy conversion is identified observationally in association with anomalous convection near the Bonin Islands.The anomalous circulation of the PJ pattern, in turn, can intensify the anomalous convective activity near the Philippines through enhancing evaporation and moisture convergence and dynamically inducing anomalous ascent. It is thus hypothesized that the PJ pattern can be regarded as a moist dynamical mode that sustains itself both via dry energy conversion and interaction with moist processes.