利用法国AVISO(Archiving, Validation And Interpretation Of Satellite Oceanographic Data)海平面异常数据，通过小波分析发现在索马里海流范围内比内区多存在一个30d周期的振荡，其可能原因是跨赤道流的不稳定。使用一个简单的等值浅水模式，在跨赤道背景流的情况下，分析了其中扰动的周期和不稳定性。通过将扰动速度利用Weber函数展开后保留前四阶，获得了频散关系。结果表明，在此区域有一类增长型的短波, 其频率接近30天，这一结果与观测相近。

Our wavelet analysis of Archiving, Validation and Interpretation of Satellite Oceanographic Data (AVISO) sea surface height anomaly reveals an oscillation with a period of 30 days, which exists only inside the western boundary current region. The mechanism may be an instability of cross-equatorial current. The research tool is a simple equivalent shallow water model in the presence of background cross-equatorial current. By expanding the perturbation equation with Weber function and keeping the first four modes, the dispersion relation in the presence of cross-equatorial current is obtained. Our instability analysis demonstrates the existence of unstable modes in this boundary current region. The most unstable shortwave has a period of approximate 30 days, which is in accordance with the AVISO observations.