台湾岛西南部一个暖涡的跨海盆粒子输运

台湾岛西南部是暖涡产生的源地之一, 以往的研究集中于讨论暖涡本身的运动特征和规律, 如暖涡的半径、产生位置、寿命、移动路径等, 暖涡生成机制也引发了深入的研究和探讨, 但关于该地区暖涡导致的物质输运, 仅有少量的观测且结果较为离散。文章通过AVISO(Archiving Validation and Interpretation of Satellite Oceanographic Data)卫星高度计的地转流场、海表高度异常数据以及区域海洋环流模式(ROMS)结果, 得到一个暖涡从2003年秋季至2004年春季的生消过程, 并在涡旋内10m、50m、100m层各放入10000个示踪粒子, 追踪它们的运动轨迹, 从而讨论暖涡的跨海盆粒子输运特征。该暖涡的寿命为121d, 平均半径50.4km, 移动路程1437.5km, 平均移动速度 13.5cm·s^-1。研究表明, 该暖涡具有较好的物质保守性, 可以将大部分的粒子裹挟在涡旋内部并携带着沿1000~2000m等深线向西南方向运动, 在该暖涡的消亡阶段, 由于地形的阻隔以及与流的相互作用, 涡的不稳定性和形变增加, 大量的粒子被甩出涡旋, 最后仅有18.6%~35.6%粒子随暖涡运动至海南岛南部。尽管这个比例并不大, 但涡致输运的积累作用不容小觑。示踪粒子的数目与位涡具有较好的相关性, 相关系数为0.63, 暖涡内的物质被位涡线裹挟着前行。示踪粒子在暖涡内呈螺旋状下沉, 大部分粒子在释放后的5d内基本在起始的深度上下浮沉, 仅有3.9%的粒子沉降至15m以下。在10m、50m和100m层释放的粒子平均深度最大值分别为48.7m、88.7m和130.6m。

Cross-basin particle transport by a warm eddy southwest of Taiwan Island

The site southwest of Taiwan Island is one of the places where warm core eddies originate. Extensive studies on warm eddies have been conducted; however, a majority of these studies focused on eddy characteristics, such as radius, generation area and lifetime. Some discussed generation mechanisms while the investigation of transport by warm eddies remains scarce. We observed a warm eddy during autumn 2003 to spring 2004 using both AVISO (Archiving Validation and Interpretation of Satellite Oceanographic Data) altimetry data and the Regional Ocean Modeling System (ROMS) output data. A total of 10, 000 particles were released inside the warm eddy at 10, 50 and 100 m, respectively. The lifespan of the warm eddy was 121 days, with a mean radius of 50.4 km; and it traveled 1437.5 km at a mean speed of 13.5 cm·s^-1. Most of the tracers were trapped inside the eddy and were carried southwestward along 1000-2000 m isobaths. Because of the terrain and its interaction with the flow, the eddy was more unstable during its terminal stage. Many of the tracers were expelled from the eddy, and the number of remaining tracers dropped to only 18.6%-35.6%. Although this ratio may seem small, the accumulative effects of transport were considerable. The number of tracers in the warm eddy had a strong positive correlation with potential vorticity (PV) with a correlation coefficient of 0.63. The tracers were trapped by the outmost PV contour The tracers inside the eddy sank in a spiral. Within the first 5 days, only 3.9% of the particles sank deeper than 15 m. The mean depth of tracer particles inside the eddy was observed to to 48.7, 88.7 and 130.6 m for those released at 10, 50 and 100 m, respectively.