The variation of vertical water movement in the tropical Pacific Ocean has great impact on regional and even global climate, ecosystem, due to its crucial role in supporting primary production, influencing carbon recycling, and modulating the coupled ocean-atmosphere system, etc. In this study, vertical velocity in the off-equatorial western Pacific Ocean warm pool is investigated using observations from an array of four subsurface moored acoustic Doppler current profilers (ADCPs) centered at 4.7°N, 142.0°E. The observations consist of horizontal velocities from December 2017 to March 2021. Vertical velocity is calculated using horizontal velocity divergence/convergence in combination with the continuity equation. The record-length mean vertical velocity is upwelling from surface down to 110 m and downwelling below that, with maximum upwelling located at the North Equatorial Countercurrent (NECC) core. The vertical velocity variability, mainly resulting from divergence and convergence of zonal currents, has much larger magnitude than the mean values. Results indicate that this variability within the thermocline is primarily associated with westward-propagating Rossby waves that generate in the eastern Pacific Ocean on seasonal time scale, while both Ekman pumping due to local wind stress curl anomaly and Rossby waves due to central and western Pacific Ocean wind forcing anomaly play important roles on interannual time scale. The variability of potential temperature and potential density structures around the thermocline depth are highly consistent with the variability in vertical velocity, whereas this good agreement is rapidly weakened near the surface.
 

vertical velocity, Pacific Ocean, temperature structure, potential structure