印度洋混合层盐度季节变化机制研究

本文利用Argo盐度、SODA海流量、OAFlux蒸发量和TRMM降水量等数据，采用盐度收支方程定量给出了印度洋混合层盐度的收支，揭示了整个印度洋净淡水通量项、平流项、垂向卷夹项的分布、季节变化特征及其对混合层盐度变化的主要贡献。结果表明，就多年平均而言，平流项负贡献（15.14%）大于正贡献（9.89%），说明平流输送把低盐水输送到高盐海域，导致印度洋高盐海域混合层的盐度降低。净淡水通量项的分布和季节变化与降水量基本一致，且正贡献（13.70%）大于负贡献（7.81%），说明净淡水通量项使印度洋的混合层盐度升高（因为多年平均蒸发量大于降水量）。盐度季节变化显著海域的进一步分析表明，6−11月，西南季风漂流把赤道西印度洋的低盐水（相对阿拉伯海高盐水而言）输送到阿拉伯海西部海域，导致该海域的盐度降低。平流输送把孟加拉湾湾口和中部的高盐水带到北部海域，是导致北部海域盐度升高的主要原因。

Mechanisms of the seasonal variability of mixed-layer salinity in the Indian Ocean

In this study, we quantify the mixed-layer salinity (MLS) budget in the Indian Ocean using the salinity budget equation along with Argo salinity, SODA ocean current, evaporation, and precipitation data. The results show that the distribution and seasonal variability for the terms of freshwater flux, advection and entrainment in the Indian Ocean, and their contributions to the variations of MLS. Regarding the climatological annual mean, the negative contribution (15.14%) of the horizontal advection term to MLS is much larger than its positive contribution (9.89%). This implies that the horizontal advection transports low-salinity water to the salty regions, resulting in a decrease in MLS there. The distribution and seasonal variability of the freshwater flux term are generally consistent with those of precipitation, with a positive contribution (13.70%) higher than negative contribution (7.81%). It suggests that the freshwater flux term increases MLS in the Indian Ocean because of the evaporation overwhelming the precipitation. Analysis on the regions with significant seasonal variations of MLS indicates that from June to November, the Southwest Monsoon Current transports low-salinity water from the western equatorial Indian Ocean to the western Arabian Sea, causing salinity in that region to decrease. The advection of high-salinity water from the southern and central to the northern of Bengal Bay is the main reason for the increase in salinity there.