Impacts of Oceanic Fronts and Eddies in the Kuroshio-Oyashio Extension Region on the Atmospheric General Circulation and Storm Track

Abstract

This paper reviews the progress in our understanding of the atmospheric response to midlatitude oceanic fronts and eddies, emphasizing the Kuroshio-Oyashio Extension (KOE) region. Oceanic perturbations of interest consist of sharp oceanic fronts, temperature anomalies associated with mesoscale eddies, and to some extent even higher-frequency submesoscale variability. The focus is on the free atmosphere above the boundary layer. As the midlatitude atmosphere is dominated by vigorous transient eddy activity in the storm track, the response of both the time-mean flow and the storm track is assessed. The storm track response arguably overwhelms the mean-flow response and makes the latter hard to detect from observations. Oceanic frontal impacts on the mesoscale structures of individual synoptic storms are discussed, followed by the role of oceanic fronts in maintaining the storm track as a whole. KOE fronts exhibit significant decadal variability and can therefore presumably modulate the storm track. Relevant studies are summarized and intercompared. Current understanding has advanced greatly but is still subject to large uncertainties arising from inadequate data resolution and other factors. Recent modeling studies highlighted the importance of mesoscale eddies and probably even submesoscale processes in maintaining the storm track but confirmation and validation are still needed. Moreover, the atmospheric response can potentially provide a feedback mechanism for the North Pacific climate. By reviewing the above aspects, we envision that future research shall focus more upon the interaction between smaller-scale oceanic processes (fronts, eddies, submesoscale features) and atmospheric processes (fronts, extratropical cyclones etc.), in an integrated way, within the context of different climate background states.

摘要

本文综述了中纬度海洋锋面和涡旋对大气环流影响的相关研究进展, 重点关注黑潮-亲潮延伸区 (KOE)的海-气相互作用。综述的海洋现象包括海洋锋面、与中尺度涡有关的海温异常、以及次中尺度变率, 而大气现象则关注边界层以上的自由大气。中纬度大气受风暴轴中剧烈的瞬变涡旋活动影响, 因此本文对大气平均基本流和风暴轴的响应进行了评估。风暴轴对海洋扰动的响应远远大于对基本流的响应, 导致基本流的响应被掩盖且难以从观测资料中识别出来。本文首先介绍了海洋锋面对风暴轴内单个气旋结构的影响, 并进一步阐述对风暴轴的整体影响。KOE区的海洋锋面有显著的年代尺度变化, 因此在年代尺度上对风暴轴和大气环流产生调控, 相关研究进展在文中进行了总结和比较。现有的海洋锋面对大气影响的研究结果仍存在很大的不确定性, 这主要是由数据分辨率不足等因素导致。近期有模式研究强调海洋中尺度涡乃至次中尺度过程对风暴轴的作用, 这是未来重要的发展方向, 但仍需要更多的验证。此外, 大气对海洋扰动的响应可以反馈海洋, 形成闭合的北太平洋海-气反馈机制。通过对上述多个研究方向的总结, 作者指出未来研究应在充分考虑不同气候背景下, 系统研究并聚焦中小尺度海洋过程 (锋面、涡旋、次中尺度过程等) 和大气过程 (锋面、温带气旋等) 的相互作用。