2000—2015年夏秋季孟加拉湾湾口区涡流相互作用能量学特征

Energy characteristics of eddy-mean flow interaction in the estuary of Bay of Bengal in summer and autumn during 2000-2015

文章主要使用全球简单海洋资料同化分析系统(Simple Ocean Data Assimilation,SODA)产出的海洋再分析数据产品和美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)发布的风场资料,通过能量学方法分析了2000—2015年夏季至秋季(6—11月)孟加拉湾涡-流相互作用特征在不同印度洋偶极子(Indian Ocean Dipole,IOD)事件发生年的表现。结果表明,在IOD负位相年更强的西南季风背景下,涡动能和涡势能的量值均较大,海洋不稳定过程更多地将平均流场的能量输向涡旋场,IOD正位相年反之。另外,研究发现孟加拉湾湾口区的涡动能在个别年份会发展出一种与气候态存在显著异常的空间分布,即在个别年份湾口中央海域异常出现涡动能极大值。通过对出现该异常现象最显著的2010年进行个例分析,发现当年的孟加拉湾海表风场发展出一个气旋式环流异常,显著地改变了海洋上层环流形态,极大地影响了平均流场与涡旋场之间的相互作用。进一步对维持涡动能平衡的各做功项进行诊断后发现,湾口异常海域涡动能年际变化的主要影响因素为海洋内部的压强做功,其次是正压不稳定过程和平流的做功,海表风应力做功项贡献较小。

Using the wind field from the Simple Ocean Data Assimilation(SODA)ocean reanalysis product and National Centers for Environmental Prediction(NCEP),we analyze the characteristics of eddy-mean flow interaction in the Bay of Bengal during summer and autumn(June-November)of 2000-2015 by means of energy analysis in different years of occurrence of Indian Ocean Dipole(IOD)anomalies.The results show that,in the context of southwest monsoon with stronger negative phase of the IOD,both eddy kinetic energy(EKE)and eddy potential energy have relatively large magnitude.In the process of ocean internal instability,more energy of the mean flow field has been transferred to the eddy field,while in the positive phase of the IOD the energy is transferred less than usual.In addition,we find that the EKE in the bay mouth area of the Bay of Bengal tends to develop a spatial distribution with significant anomalies of the climate state in negative IOD anomaly years,that is,the EKE maxima appears around(88°E,5°N).A case study of 2010 when the EKE anomaly was most prominent reveals that a cyclonic circulation anomaly was developed in the surface of the Bay of Bengal,which significantly changed the upper-ocean circulation pattern and greatly affected the interaction between the mean flow field and the eddy field.After further diagnosis of each term that maintains the EKE balance,we find that the main influencing factor of interannual change of EKE in the bay mouth area was the pressure term inside the ocean,followed by the unstable barotropic process and the advection term;and the contribution of sea surface wind stress was minimal.