摘要
根据对卫星观测的海平面高度资料的分析,进一步证实了在北太平洋副热带两支向东的流(副热带逆流和夏威夷背风逆流)所在的区域内,海平面高度的70-210天周期振荡是主要的低频变化.发现在这两支向东的逆流区Rossby波的特性不同:副热带逆流区70-210天周期振荡对应的Rossby波西传过程中增幅,在台湾以东振幅达到最大;而在夏威夷背风逆流区,70-210天周期Rossby波在西传过程中不出现增幅现象.依据2.5层海洋模式得到的关于Rossby波振幅、频率与海洋层结之间的关系,揭示了周期为70-210天的Rossby波为不稳定波,这是由于副热带逆流海域模态水存在使得密度的垂直梯度变小的缘故;而在夏威夷背风逆流区位于表层逆流下的北赤道流西深东浅,70-210天周期Rossby长波在逆流的东部有可能不稳定,但其在逆流的西部是稳定的,因此不出现在西传过程中增幅现象;发现在北太平洋副热带两个向东流的海域,年周期Rossby波是稳定的,因此,在该海域海平面周期为70-210天的振荡的振幅要比年周期振荡的振幅大.
Based on the analysis of Sea Surface Height Anomaly （SSHA） from satellite observation, it is proved that the oscillation with period of 70 - 210 days is dominating in two branches of the eastward countercurrent in Subtropical North Pacific： Subtropical Countercurrent （STCC） and Hawaiian lee Countercurrent （HLCC）. It is found that in the STCC the amplitude of the Rossby wave, corresponding to the SSHA oscillation with period of 70 - 210 days, increases when the wave propagates westward, and the amplitude is the largest in east of Taiwan. In HLCC, the amplitude of Rossby wave with period of 70 - 210 days doesn＇t increase when the wave propagates westward. Based on the relation of Rossby wave＇s growth rate with mean current and stratification from 2.5-layer model, it is revealed that in STCC area the Rossby wave with period of 70- 210 days is unstable and the amplification mechanism of Rossby wave is baroclinic instability, because there is low potential vorticity water under STCC and the vertical gradient of density is smaller than that in HLCC. Since there is no low potential vorticity water the Rossby wave with period of 70 - 210 days is stable in the west of HLCC, there is no amplification event when Rossby wave propagates westwards in HLCC. In STCC and HLCC, the Rossby wave with 1 year period is always stable, its amplitude is smaller than that of the unstable Rossby wave with period of 70 - 210 days.
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第1期83-91,共9页
Chinese Journal of Geophysics
基金
国家自然科学基金重点项目(40333030)资助
关键词
北太平洋
副热带逆流
夏威夷背风逆流
ROSSBY波
斜压稳定性
North Pacific, Subtropical Countercurrent, Hawaiian Lee Countercurrent, Rossby wave, Baroclinic stability
