热带太平洋水位和海流对不同风场响应的模拟研究

A MODELING STUDY OF THE RESPONSE OF SEA LEVEL AND SURFACE CURRENTS TO DIFFERENT WIND FIELDS IN THE TROPICAL PACIFIC

本文用二维绝热模式研究了El Nio发生前后热带太平洋表层流系和水位对两种不同风场的响应。多年平均夏季(7月)风场是用1950～1979年期间COADS资料统计得到的,El Nio期间(7月)风场也是根据同一资料,把1950～1979年期间6个强El Nio年合成得到的。模拟的表层流系(包括北赤道流、北赤道逆流、南赤道流)的位置与实际基本一致。水位也与Wyrtki(1974)等人计算结果吻合得较好。El Nio期间,在风场发生变化的情况下,计算结果是:北赤道流和北赤道逆流加强,南赤道流减弱;西太平洋出现以北赤道逆流槽为中心的大面积水位负距平,东太平洋水位普遍升高,没有明显的中心。本文对这些变化的原因进行了初步的分析和讨论。

In this paper the response of sea level and surface currents in the tropical Pacific to different wind fields before and during El Nino event has been studied by using a two dimensional model. The long term mean wind field was obtained by using COADS data from 1950 to 1979 and the wind field of El Nino year was obtained by compositing six strong El Nino events during period 1950～1979 based on the same data. The modeling results show that the location of surface currents including the North Equatorial Current, the North Equatorial Countercurrent and the South Equatorial Current and the sea level basically coincide with the observation and calculation of Wyrtki (1974). Calculations using the wind fields of El Nino year show that the zonal component of the North Equatorial Current and the North Equatorial Countercurrent increases and the South Equatorial Current decreases, and negative sea level anomalies appear in most of western tropical Pacific the center of which is located along the North Equatorial Countercurrent Trouth, and positive anomalies are widespread throughout the eastern tropical Pacific with no evident anomaly center. Calculations indicate that the deepening of North Equatorial Countercurrent Trough and the weakening of Equatorial Ridge resulted from the positive vorticity anomaly of wind stress in the low atmosphere layer while the streng-thening of North Equatorial Ridge resulted from the negative vorticity anomaly of wind stress.