The Asymmetric Atmospheric Response to the Decadal Variability of Kuroshio Extension during Winter

Abstract

The Kuroshio extension (KE) exhibits interdecadal variability, oscillating from a stable state to an unstable state. In this paper, ERA-Interim reanalysis data are used to discuss the possible reasons for the asymmetric response of the atmosphere to symmetric sea surface temperature anomaly (SSTA) during periods of differential KE states. The analysis has the following results: the SSTA presents a nearly symmetrical distribution with opposite signs during the KE stable and unstable periods. During the KE stable period, the storm track is located north of 40°N and is significantly enhanced in the northeast Pacific Ocean. The atmospheric response is similar to the West Pacific/North Pacific Oscillation teleconnection (WP/NPO like pattern) and presents a barotropic structure. The inversion results of the potential vorticity equation show that the feedback of transient eddy vorticity manifests a WP/NPO like pattern and presents a barotropic structure, which is the main reason for bringing about the response of the WP/NPO like pattern. The magnitude of the feedbacks of both diabatic heating and transient eddy heating is small, which can offset one another. During the KE unstable period, the main body of the storm track is located to the south of 40°N, and there is no significant response signal in the atmosphere, except near the west coast of North America. Compared with the KE stable period, the asymmetry of response of the transient eddy vorticity is the main reason for the asymmetric response of the atmosphere.

摘 要

黑潮延伸体KE (Kuroshio Extension) 具有从稳定状态到不稳定状态的年代际变率. 本文利用ERA-Interim再分析资料探讨了大气对KE不同稳定时期海温异常的不对称响应的可能原因. 结论如下:KE稳定型和不稳定型期间海温异常SSTA (Sea Surface Temperature Anomaly) 基本呈现符号相反的对称型分布. KE稳定型期间, 风暴轴主体位置偏北, 并在东北太平洋显著增强, 大气的响应表现为类似WP/NPO (Western Pacific / North Pacific Oscillation Teleconnecton)型, 并呈现正压结构. 位涡方程的反演结果显示, 瞬变涡旋涡度反馈呈现出了类似WP型响应且为正压结构, 是WP/NPO型响应维持的主要原因. 非绝热加热与瞬变涡旋加热反馈量级较小, 大体上可相互抵消。KE不稳定型期间, 风暴轴主体位置偏南, 大气未能出现显著的响应信号, 与KE稳定型时期相比, 瞬变涡旋涡度反馈响应的不对称是形成大气非对称响应的主要原因.