Long baroclinic Rossby waves with periods of about 500 d near 20 N in the northwest Pacific Ocean

On the basis of maps of sea level anomalies data set from October 1992 to January 2004, pronounced low frequency variations with periods of about 500 d are detected in the area near 20 degrees N from 160 degrees W to 130 degrees E. A linear two-layer model is employed to explain the mechanism. It is found that the first-mode long baroclinic Rossby waves at 20 degrees N in the northwest Pacific propagate westward in the form of free waves at a speed of about 10.3 cm/s. This confirms that the observed low frequency variabilities appear as baroclinic Rossby waves. It further shows that these low frequency variabilities around 20 degrees N in the northwest Pacific can potentially be predicted with a lead up to 900 d.