Atmospheric intraseasonal variability at the surface in the tropical western Pacific Ocean

Observations from the Tropical Atmosphere Ocean (TAO) moored buoy array provide an unprecedented opportunity to explore the atmospheric variability at the tropical sea surface. Three years of data from the TAO buoys in the western Pacific are analyzed to document surface intraseasonal fluctuations and their relationships to the tropical intraseasonal oscillation (ISO) in the troposphere above the boundary layer. The most robust intraseasonal variations at the surface are observed in zonal wind, wind speed, relative humidity, sea surface temperature (SST), surface turbulent sensible and latent heat fluxes, and air-sea temperature and humidity differences. Less robust intraseasonal signals are found in surface meridional wind, specific humidity, and equivalent potential temperature. Observed signals in surface air temperature and wind divergence are the weakest. Positive anomalies of atmospheric deep convection associated with the ISO tend to occur in regimes of surface westerly perturbations, where positive anomalies of surface wind speed, humidity, equivalent potential temperature, and negative anomalies of surface air temperatures are also observed. A near-quadrature relation exists between SST and atmospheric deep convection with the maximum (minimum) convection coinciding with the most rapid decrease (increase) in SST. Positive anomalies of surface turbulent heat fluxes and surface wind convergence slightly lead the positive anomalies of convection and wind speed. The phase difference between surface heat fluxes and wind speed is explained by the substantial intraseasonal fluctuations in air-sea temperature and humidity differences, which indicate that the degree of air-sea disequilibrium varies. The intraseasonal variability at the surface is more closely related to the intraseasonal variability in atmospheric deep convection than in low-tropospheric zonal wind, even though the wind field exhibits the most robust intraseasonal signals. The intraseasonal variations at the surface cannot always be interpreted as passive responses of the surface to deep convection; they may play active roles in the ISO above the boundary layer. Other implications of the observations for theories and numerical simulations of the ISO are also discussed.