Quasi-biennial Oscillation of the Kuroshio intrusion at Luzon Strait

Using altimeter data of the western Luzon Strait region, one dominant patterns of variability are determined by applying Fast Fourier transform analysis methods. A statistically significant propagating mode of variability with a timescale close to biennium is found. Via analysis of two different wind products, we found that this low-frequency oscillation has nothing to do with the external wind forcing. To explain the physics of the apparent preference for variability at this timescale, we investigate the stability of barotropic western Pacific circulation by using a 1.5-layershallow-water equation model. There appears to be the steady penetration of the Kuroshio become unstable to oscillatory modes, which has a timescale of 2 years for reasonable parameters. Through the stability analysis, this variability is due to the existence of large-scale barotropic instability of the mean Kuroshio path near the Luzon Strait.