Using the Argo float data, changes in the temperature and salinity in the oceanic mixed layer corresponding to the passage of intraseasonal-scale disturbances were examined over the western North Pacific (WNP) intertropical convergence zone (ITCZ) region. Events where the near-surface temperature decreased by more than 1¿C within a 10-day period were identified, corresponding to the intraseasonal variability (ISV) of the atmosphere. Analyzing the vertical profiles and the T-S relationships of the mixed layer revealed that the water was cooled mainly by mechanical mixing and Ekman upwelling related to the strong sea surface wind. Thermal cooling at the sea surface does not appear to be a predominant process in the abrupt cooling. Such cooling events were observed only when the mixed layer was shallow.