利用NCEP海洋数据和COADS海气通量资料, 通过诊断分析, 揭示了海表热力强迫、垂直夹卷、埃克曼平流和地转平流效应在北太平洋副热带模态水形成过程中的贡献。研究表明, 在北太平洋副热带3个模态水形成海域冬季混合层降温过程中, 海表热力强迫和垂直夹卷效应是主导因素, 二者的相对贡献分别约为67%和19%(西部模态水)、53%和21%(中部模态水)、65%和30%(东部模态水); 并且在东部模态水形成海域, 埃克曼平流和地转平流皆是暖平流效应, 而在西部和中部模态水形成海域, 仅有地转平流是暖平流效应。进一步的分析表明, 海洋平流(地转平流、埃克曼平流)对北太平洋副热带模态水形成海域秋、冬季混合层温度的年际、年代际异常有显著影响, 在西部模态水形成海域, 海表热力强迫(62%)和地转平流(32%)是导致混合层温度年际、年代际变化的主要因子; 在中部模态水形成海域, 混合层温度的年际、年代际变化是埃克曼平流(32%)、地转平流(30%)和海表热力强迫(25%)共同作用的结果; 相对而言, 东部模态水形成海域混合层温度的年际、年代际异常主要受海表热力强迫(67%)控制。
Diagnostics of the contributions from the surface heat forcing, vertical entrainment, Ekman advection, and geostrophic advection to the formation of the North Pacific subtropical mode water are performed using the National Centers for Environmental Prediction (NCEP) ocean data and the Comprehensive Ocean-Atmosphere Data Set ( COADS) fluxes. The results suggest that both the surface heat forcing and vertical entrainment dominate the cooling tendency of the wintertime mixed layer in all three mode water formation regions, with relative contributions of 67% and 19% in the North Pacific Subtropical Mode Water (NPSTMW) formation region, respectively; 53% and 21% in the North Pacific Central Mode Water (NPCMW) formation region, and 65% and 30% in the Eastern Subtropical Mode Water (ESMW) formation region. In addition, both the Ekman and geostrophic advection are warm advection in the ESMW formation region, while only the latter is warm advection in the other two mode water formation regions. Further analysis indicates that on interannual and decadal timescales, contributions from the surface heat forcing and geostrophic advection to the wintertime mixed layer cooling trend are 62% and 32% in the NPSTMW formation region, respectively. In the NPCMW formation region, the interannual and decadal variability derives from the combination of Ekman advection (32%), geostrophic advection (30%), and surface heat forcing (25%). By contrast, the surface heat forcing is the most prominent contributor (67%) in in ESMW formation region.
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