Oka Eitarou, Sugimoto Shusaku, Kobashi Fumiaki, Nishikawa Hatsumi, Kanada Sachie, Nasuno Tomoe, Kawamura Ryuichi, Nonaka Masami
Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan.
Department of Geophysics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai, Japan.
Sci Adv. 2023 Sep 15;9(37):eadi2793. doi: 10.1126/sciadv.adi2793. Epub 2023 Sep 13.
Subtropical Mode Water (STMW), characterized by vertically uniform temperature of ~17°C, is distributed horizontally over 5000 kilometers at the 100- to 500-meter depths in the subtropical North Pacific Ocean. Its formation and spreading fluctuate in relation to the Pacific Decadal Oscillation and the Kuroshio path variation, but the feedback from STMW on the sea surface temperature (SST) and the overlying atmosphere remains unclear. Using Argo profiling float data, we show that STMW south of Japan, whose thickness varies decadally, modulates the overlying thermal structure throughout the year by increasing isotherm uplift with increasing thickness. The STMW-induced decadal temperature change has a magnitude of up to ~1°C and is large in the warm season in the presence of the seasonal thermocline. Furthermore, 50-year observations, together with numerical simulation, show that SST, upper ocean heat content, and typhoon intensification rate have been significantly lower in years with thicker STMW and higher in years with thinner STMW.
副热带模态水（STMW）的特征是温度在17°C 上下垂直均匀，在北太平洋亚热带100至500米深度水平分布超过5000公里。其形成和扩散随太平洋年代际振荡和黑潮路径变化而波动，但其对海面温度（SST）和上层大气的反馈仍不清楚。利用Argo剖面浮标数据，我们发现日本以南的STMW厚度呈年代际变化，通过随着厚度增加等温线上升，全年调节上层热结构。STMW引起的年代际温度变化幅度高达1°C，在存在季节性温跃层的暖季变化较大。此外，50年的观测以及数值模拟表明，在STMW较厚的年份，SST、上层海洋热含量和台风增强率显著较低，而在STMW较薄的年份则较高。
