西北太平洋夏季海洋热浪的变化特征及海气关系

全球增暖背景下更加频繁和持续的海洋热浪事件已经对生态和人类社会经济造成了严重影响。但对于海洋热浪的海气相互关系和对区域气候制作用的研究还十分有限。本文基于1982—2017年美国国家海洋和大气管理局逐日最佳插值海表温度和美国国家环境预测中心再分析资料, 采用经验正交函数展开等统计方法, 系统地分析了西北太平洋夏季海洋热浪的时空分布特征及与之相联系的海气关系。结果表明, 西北太平洋夏季海洋热浪日数和次数EOF(Empirical orthogonal function)第一模态在除黑潮和黑潮延伸区外的区域呈线性增加趋势, 第二模态则呈南北反向分布, 并具有明显的年代际变化特征。海洋热浪的最大强度、持续时间、累积强度第一模态也呈线性上升趋势, 最大强度和累积强度在高纬地区上升最多, 持续时间在黑潮和黑潮延伸区变化最明显。从海气关系的角度来看, 中低纬地区出现海洋热浪事件时, 海气之间主要表现为海洋对大气潜热感热通量的增加, 从而对周边区域大气环流产生影响; 而高纬度地区出现海洋热浪事件时, 海气之间则主要表现为大气对海洋的影响, 以长波辐射和感热通量变化为主。

Variation of summer marine heatwaves in the Northwest Pacific and associated air-sea interaction

More frequent and persistent marine heatwaves (MHWs) under global warming have exerted severe ecological and socioeconomic impacts. However, there are still limited studies on the air-sea interaction related to MHWs and how MHWs modulate regional climate. Spatiotemporal distribution of summer MHWs in the Northwest Pacific (NWP) and associated air-sea interaction were systematically studied based on daily Optimum Interpolation Sea Surface Temperature (OI SST) dataset from the National Oceanic and Atmospheric Administration (NOAA) and reanalysis dataset from the National Centers for Environmental Prediction (NCEP) during the period of 1982-2017. Empirical orthogonal function (EOF) analysis of MHWs' frequency shows a linear increasing trend in the first mode except for the Kuroshio extension region, while a north-south “dipole” pattern appears in the second mode, with characteristic of inter-decadal oscillation. Maximum intensity, duration, and cumulative intensity of MHWs all show a linear increasing trend. Maximum intensity and cumulative intensity rise most in the high latitudes, and the duration of MHWs varies significantly in the Kuroshio extension region. Analysis of air-sea interaction illustrates that, when MHWs occur in the mid or low latitudes, latent heat and sensible heat fluxes from the ocean to the overlying atmosphere play a dominant role, which impacts atmospheric circulation in the surrounding area. The atmospheric forcing is more significant when MHWs occur in the high latitudes, including longwave radiation and sensible heat fluxes.