全球海洋环流模式中上层海洋对表面强迫的响应和调整 Ⅱ.年代际变率

The upper-ocean response and adjustment to surface forcing in an oceanic general circulation model II. Decadal-to-interdecadal variability

利用一个较高分辨率的全球海洋环流模式在COADS1945～1993年逐月平均资料的强迫下对海温和环流场进行了模拟,分析了北太平洋海温和环流场的年代际变化特征,同时诊断了197677年代际跃变过程中海温场变化的机制.模式模拟出了北太平洋海温年代际异常的主要模态以及197677年跃变前后的演变特征,模拟的北太平洋中部、加州沿岸和KOE区的海温异常的强度和演变趋势均和观测比较一致;同时,模式重现了分别始于20世纪70和80年代的中纬度海温异常信号沿等密度面向低纬地区的两次潜沉过程.在表层,流场的异常主要表现为与风应力异常基本符合Ekman关系的一个异常海洋涡旋,而整个上层海洋平均的流场异常则表现为两个海洋涡旋的异常,其中副热带海洋涡旋的异常的强度要显著于副极地海洋涡旋的异常,而副极地海洋涡旋异常出现的时间比副热带海洋涡旋晚3a左右的时间.对197677年前后3个区域上层海温各贡献项的诊断结果表明,北太平洋中部变冷主要是水平平流和热通量异常贡献的结果;而加州沿岸变暖主要归因于热通量的贡献;在KOE区,垂直平流、热通量和水平平流三者都起了重要作用,其中水平平流异常对这一区域海温年代际跃变出现的时间起了至关重要的作用.

Decadal-to-interdecadal variability of the temperature and circulation in the North Pacific Ocean, as well as the mechanisms of temperature evolution in the 1976-77 regime shift are investigated with a high resolution oceanic general circulation model forced with COADS 1945~1993 monthly mean data. The model successfully captures the dominant mode of the SST anomalies on the decadal-to-interdecadal timescales, as well as the major feature of SST anomalies in the 1976-77 regime shift. The time series of the simulated SST anomalies in three key regions (central North Pacific, coast of California and KOE region) were found consistent well with the observations. The model also successfully reproduces two distinct subduction events for the mid-latitude temperature anomalies in 1970s and 1980s, respectively. For the surface ocean, the dominant decadal mode in the circulation anomalies displays an oceanic gyre that consists with the wind stress anomalies by Ekman relation. But for the whole upper-ocean, two oceanic gyres were found dominant, the subtropical and subpolar gyres. The subtropical gyre is more prominent than the subpolar gyre, and the anomaly of the subpolar gyre delays the subtropical gyre by about 3 years. Examination of the upper-ocean heat budget in three key regions reveals that the 1976-77 regime shift was caused by both the sustained heat flux input anomalies and the strong horizontal advection anomalies in the central North Pacific. In the Californian coastal region, only the heat flux input anomalies were found dominant, and the effect of the horizontal advection anomalies is negligible. In the KOE region, the vertical advection, heat flux and horizontal advection anomalies are all important in producing the regime shift and the horizontal advection anomalies were found crucial for the time of the regime shift.