Variation of sea surface height at periods of 65-220 days in the subtropical gyre of the North Pacific

Variations of sea surface height (SSH) in the North Pacific Subtropical Countercurrent (STCC) region have been investigated using altimeter-derived SSH anomaly data during 1992-1999. It is shown by spectral analyses that the dominant temporal scale of SSH variations in the STCC region is 65-220 days. The energy of the SSH variations in this period band is mostly confined to the subtropical gyre and enhanced in the STCC, the Kuroshio and the Kuroshio Extension east of the Shatsky Rise. The broad energetic band in the STCC region can be divided into two regions: one is located in the latitudinal range of 2°-26° N and extending zonally from the Philippine Sea to ∼190° E along 22° N, and the other extends from around 145° E to the west of the Hawaiian Islands along 19.5° N, slightly tilting northward toward the east. The axes of these two high-variability tongues are in agreement with those of the STCC multiple bands estimated from climatological hydrographic data. The 65-220 day variations in the STCC region are characterized by westward propagating mesoscale disturbances with wavelengths of 400-1800 km. In terms of ratio of the advective speed to the phase speed the mesoscale variations can be classified into two types, i.e., nonlinear eddies with wavelengths of ∼500-700 km and quasi-linear wave motions with longer wavelengths of ∼1200 km.