基于高度计和漂流浮标数据的墨西哥湾东南部暖涡融合过程研究

Investigating the anticyclonic eddy merger process in southeastern Gulf of Mexico using altimeter and drifting buoy

本文结合卫星高度计和漂流浮标数据,采取海表面高度法发现并跟踪了墨西哥湾东南部附近发生的一次暖涡融合事件,通过该典型暖涡融合过程的研究初步揭示了涡间融合作用模式,有助于进一步理解复杂涡旋作用机制。欧拉涡旋结果显示,一对暖涡彼此吸引并伴随传播3周以上,随后融合为统一涡旋结构并继续向西传播。被其捕获的浮标提供了融合前后的拉格朗日涡旋轨迹,在融合发生前8天时,一个浮标随水流交换切换了原本追随的暖涡,表明融合事件被高度计观测到之前,涡间水体交流作用已经比较显著。融合前后,欧拉涡旋和拉格朗日涡旋半径均存在较大改变,其中欧拉半径提升了96.2%,受两个暖涡牵引的漂流浮标的拉格朗日半径分别提升了49.1%和115.6%。受融合效应影响,海表面温度场也表现出不同的环境响应,进一步验证了融合过程的发生。最后,对融合前后动能、涡度和散度等动力学演变,以及半径、振幅和形状等形态学变化的分析表明:融合大致经历了涡旋渐近、水体交流、轮廓压缩形变、拉长椭圆涡旋生成和边界重塑等过程;涡心所在平面的垂直结构主要表现为由双峰向单峰的演变;涡旋融合后实现了能量向中尺度的逆级联;受限于单核涡结构,在融合过程中部分属性统计存在偏差,可能导致事件前后发生突变。

Combining satellite altimetry and drifter data,the method of sea surface height to discover and track an anticyclonic eddy merger event that occurred near the southeastern Gulf of Mexico was used in this study.By study-ing this typical anticyclonic eddy merger process,the mode of eddy merging is preliminarily revealed,which helps to further understand the complex eddy mechanism.The Eulerian eddy results show that pairs of anticyclonic ed-dies attract each other and propagate together for more than three weeks before merging into a unified eddy struc-ture and continuing to propagate westward.The Lagrangian vortex trajectories captured by drifters provide evid-ence of water exchange between the vortices before the merger,as one drifter exchanged its original anticyclonic eddy on November 15,indicating significant water exchange between the vortices before being observed by the alti-meter.Before and after the merger,the radii of the Eulerian and Lagrangian vortices both increased significantly with the Eulerian radius improving by 96.2%and the Lagrangian radius of the drifting buoys pulled by two anticyc-lonic eddies improving by 49.1%and 115.6%,respectively.The sea surface temperature field also exhibited differ-ent environmental responses due to the merging effect,further verifying the occurrence of the merger process.Fi-nally,the analysis of the dynamic evolution of kinematics such as kinetic energy,vorticity,and divergence before and after the merger,as well as the morphological changes such as radius,amplitude,and shape,showes that the merger roughly experienced processes such as vortex asymptote,water exchange,contour compression and deform-ation,elongated elliptical vortex generation,and boundary reshaping.The vertical structure of the plane where the vortex is located mainly shows evolution from bimodal to unimodal.After the vortex merger,energy is transferred to the mesoscale through inverse cascade.Due to the single-core vortex structure,some statistical properties are biased during the merging process,which may have led to abrupt changes before and after the event.