黑潮上游海區衛星測高觀測：渦漩之決定及分析

Abstract

本文是利用TOPEX/POSEIDON (T/P)、 ERS-1 及 ERS-2測高資料來研究台灣東部之黑潮及黑潮上游海區（KUDEX）之渦漩，本區之geoid以衛星測高及船測資料求得，並用8年的T/P資料，以每隔10天之重覆軌道來求黑潮運通量、寬度、中心流速及位置之時間序列。由黑潮的時間序列得知半年、一年及跨年的變異量可能是受渦漩的干擾、季風、太陽活動及ENSO影響。T/P求得之台灣東部黑潮平均運通量為19 Sv，和實際量測之WOCE PCM-1結果一致。台灣東部黑潮之中心軸會隨著季節變化，一般來說，秋季時中心軸靠近東海而夏季則遠離東海靠近琉球島弧。海水面高度異常也有一年及跨年的變化，而後者則與ENSO十分相關。在El Niño事件期間，東風逐漸減弱，造成海水面異常升高以及冷渦漩幾乎消失。在KUDEX上的洋流是以每10天為一個間隔來計算，而洋流的形狀可以反映出海洋表面的溫度、風應力旋度與渦漩動能。在西元1993~2000期間，KUDEX上的冷漩渦與暖漩渦是由人工判斷與最小二乘法來辨識。這些渦漩動力特徵的計算與分析也與時間、地點及渦漩半徑有關。根據知名的海洋物理學指出，暖渦漩或冷渦漩將會向西移至亞洲大陸，為了偵測KUDEX地區渦漩之行進路徑，吾人以選定二個渦漩求得移動速度，並了解其 動力特性、渦漩之演變，及渦漩與台灣東部黑潮的相互關係。

Altimeter data from TOPEX/POSEIDON (T/P), ERS-1 and ERS-2 are used to study the Kuroshio Current east of Taiwan and eddies in the Kuroshio Upstream Dynamics EXperiment (KUDEX) area. A geoid model derived altimeter and ship data, and 8 years of 10-day repeat T/P data were used to compute time series of Kuroshio’s volume transport, width, axis velocity and axis location. These Kuroshio time series show semi-annual, annual and inter-annual variations, which are probably caused by eddy disturbance, moonsoonal winds, solar activity and ENSO. The averaged volume transport of the Kuroshio east of Taiwan is 19 Sv and is consistent with the in situ measurement at the WOCE PCM-1 line. East of Taiwan the axis of the Kuroshio varies with seasons, and in general in autumn the axis moves closer to the East China Sea while in summer the axis is away from East China and near the Rykyu Islands. Sea level anomaly (SLA) over KUDEX also has annual and inter-annual variations, and the later is closely linked to ENSO. During an El Niño event, easterly wind weakens, SLA is unusually high and cold eddies almost disappear. Ocean circulations over KUDEX at a 10-day interval are computed and the patterns of circulations are examined with respect to sea surface temperature, wind stress curl and eddy kinetic energy. Cold-cored and warm-cored eddies over KUDEX during 1993-2000 are identified by a combination of human judgment and a least-squares method. The kinematic properties of these eddies are also computed and analyzed in relation to time, location and eddy radius. Due to the well-known ocean physics, a warm-cored or cold-cored eddy created over KUDEX will move westwards to the Asia continent. Detailed traveling paths, moving velocities of two selected eddies are studied to understand the dynamics and the evolution of an eddy over KUDEX and how it interacts with the Kuroshio Current east of Taiwan.