The relation between the Mindanao Current and Mindanao Undercurrent on seasonal scale
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摘要: 基于OFES数值产品,对棉兰老流(MC)和棉兰老潜流(MUC)的流量进行了计算,探讨了二者在季节尺度上的关系。通常而言,MUC由南太平洋热带水(SPTW)的深层部分和南极中层水(AAIW)组成,而本文中,我们将1500米以深的北向流核也作为MUC的一部分来进行讨论,将其称之为高位势密度水(HPDW)。由于考虑了水团的性质,同时采用盐度和位势密度为限制来计算MC和MUC的流量更为合理。OFES气候态年平均状态下,MC的流量为37.40±5.81 Sv,而MUC的流量在26.5至27.7 σθ之间为23.92±6.47 Sv,在26.5至27.5 σθ之间则为17.53±5.45 Sv。MC和MUC的变化在季节上表现出较好的相关性:MC在春季较强而在秋季较弱,这与MUC的季节变化相似,在OFES结果中二者的相关系数为0.67,相同的结果也出现在HYCOM模式结果中。通过设计改变低纬度太平洋纬向风场的两个敏感性实验,探究了MC和MUC的关系。结果表明:随着MC的加强,海水的斜压性增强,MUC (26.5< σθ< 27.7)也随之增强,其增强的主要部分为深层的HPDW,而AAIW基本不变,SPTW减弱,反之亦然。Abstract: The ocean general circulation model for the earth simulator (OFES) products is applied to estimate the transports of the Mindanao Current (MC) and the Mindanao undercurrent (MUC) and explore the relation between them on seasonal scale. In general, the MUC is composed of the lower part of the Southern Pacific Tropical Water (SPTW) and Antarctic Intermediate Water (AAIW). While the deep northward core below 1 500 m is regarded as a portion of MUC. Both salinity and potential density restrictions become more reasonable to estimate the transports of MC/MUC as the properties of water mass having been taken into consideration. The climatological annual mean transport of MC is (37.4±5.81)×106 m3/s while that of MUC is (23.92±6.47)×106 m3/s integrated between 26.5σθ and 27.7 σθ, and (17.53±5.45)×10106 m3/s integrated between 26.5 σθ and 27.5 σθ in the OFES. The variations of MC and MUC have good positive correlation with each other on the seasonal scale: The MC is stronger in spring and weaker in fall, which corresponds well with the MUC, and the correlation coefficient of them is 0.67 in the OFES. The same variations are also appeared in hybrid coordinate ocean model (HYCOM) results. Two sensitive experiments based on HYCOM are conducted to explore the relation between MC and MUC. The MUC (26.5< σθ< 27.7) is strengthening as the MC increases with the enhancement of zonal wind field. It is shown, however, that the main part of the increasement is the deeper northward high potential density water (HPDW), while the AAIW almost remains stable, SPTW decreases, and vice versa.
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Key words:
- Mindanao Current /
- Mindanao Undercurrent /
- potential density /
- transport /
- seasonal variability
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