增温停滞背景下黑潮与湾流区域潜热通量年代际趋势变化差异及其成因分析

Differences of the Interdecadal Trend Shifts of Latent Heat Fluxes in Kuroshio and Gulf Stream Regions in the Warming Hiatus Background and the Possible Mechanisms

本文使用美国伍兹霍尔海洋研究所发布的客观分析海气通量项目数据集及日本海洋科学技术中心的Ishii次表层温盐数据,利用经验正交函数分析方法、小扰动展开、线性回归、海水热力学方程2010等方法,主要研究在增温停滞背景(1979~2000年,升温阶段;2001~2013年,停滞阶段)下,北半球两支西边界流区域即黑潮及其延伸区域(简称黑潮区域)和墨西哥湾流区域(简称湾流区域)海表潜热通量的年代际趋势转变和影响因子,以及内部热含量的年代际变化。结果表明,两支西边界流在增温停滞背景下都发生了年代际尺度的趋势反转,而反转的时间节点以及前后的反转趋势都不相同:黑潮区域潜热通量年代际趋势于2001年左右由正转负;而湾流区域潜热通量年代际趋势于1993年左右由负转正。其影响因子在前后阶段也有不同:通过影响海表饱和比湿进而影响海气比湿差,海表温度是影响黑潮区域全时间段以及湾流区域1993~2013年时间段潜热通量变化的主要因素;而风速通过直接的影响以及对空气湿度的影响也会对潜热通量变化产生间接影响,主要在湾流区域的1979~1992年时间段体现。黑潮及湾流区域0~1000 m海水热含量的年代际变化同样存在差异:黑潮区域表层热含量年代际变化同混合层一致;湾流区域表层热含量年代际变化同深层相异,而表层以下的变化较为一致;两个区域的深层热含量变化都体现了增温停滞的现象,黑潮区域可能存在下层至上层的影响;而湾流区域可能存在上层至下层的影响。黑潮与湾流区域表面的差异可以归结为海洋与大气因素的影响差异,而内部热含量年代际变化的垂直差异可能归结为两区域的结构差异。增温停滞对两区域的变化影响显著,而区域的变化可能存在对增温停滞的反馈。

The authors researched the interdecadal trend shifts of latent heat flux(LHF)over the Kuroshio Extension(KE)and Gulf Stream(GS)regions during the warming and warming hiatus periods using the LHF data and relevant variables obtained from the Objectively Analyzed Air–Sea Fluxes Project of the Woods Hole Oceanographic Institution and the Ishii subsurface temperature and salinity data obtained from the Japan Agency for Marine–Earth Science and Technology.The small perturbation method,empirical orthogonal function analysis,and International Thermodynamic Equation of Seawater—2010 are applied in this research.Contrasting interdecadal trend shifts of LHF exist in the KE and GS regions.The interdecadal LHF trend of the KE region shifts from positive to negative around 2001,whereas that of the GS region shifts from negative to positive around 1993.The variation of the KE region primarily resulted from sea surface temperature change(ocean-induced),whereas that of the GS region resulted from wind speed(1979–1992;atmosphere-induced)and sea surface temperature(1993–2013).The interdecadal variations of ocean heat content(OHC)in the KE and GS regions are also different:The interdecadal variation of surface heat content in the KE region is consistent with the mixed layer,whereas that in the GS region is different from that in the deep layer.Meanwhile,the changes below the surface layer are more consistent.The internal heat content changes in both regions reflect the warming hiatus phenomenon.The internal heat content in the KE region influences first the lower layer and then the upper layer,whereas that in the GS region influences first the upper layer and then the lower layer.The difference between the surfaces of the KE and GS regions can be attributed to the difference between ocean and atmospheric factors.Moreover,the vertical difference of the interdecadal variation of internal heat content can be attributed to the structural difference between the two regions.All of these variations are associated with the warming hiatus and may affect the warming hiatus conversely.