Free and forced Rossby waves in the western South China Sea inferred from Jason-1 satellite altimetry data

Data from a subsurface mooring deployed in the western South China Sea shows clear intra-seasonal oscillations (ISO) at the period of 40 similar to 70 days. Analysis of remotely-sensed sea surface height (SSH) anomalies in the same area indicates that these ISO signals propagate both eastward and westward. Time-longitude diagrams of ISO signals in SSH anomalies and wind-stress curl indicate that the eastward propagating SSH anomalies is forced by wind-stress curl. This is also confirmed by lag correlation between SSH anomalies and the wind-stress-curl index (wind stress curl averaged over 109.5 degrees E-115 degrees E and 12 degrees N-13.5 degrees N). Lag correlation of SSH anomaly suggests that the westward propagating signals are free Rossby waves.