In this study, we investigate the roles of freshwater flux (particularly precipitation) anomaly in SST anomalies associated with ENSO in a coupled system using a state-of-the-art climate model, MIROC6. In addition to the control experiment (CTRL), where the atmosphere and ocean are fully coupled everywhere, two sensitivity experiments are conducted where freshwater flux over the tropical Pacific Ocean is partially replaced with the 3-hourly climatology from CTRL. In the Pclim/Eclim experiment, the precipitation/evaporation flux into the ocean is replaced over the tropical Pacific (the atmosphere can "feel" the ocean variations everywhere). It is found that ENSO variability significantly reduces (up to about 17% for Niño3.4), particularly in the developing season without precipitation anomaly, while evaporation anomaly does not significantly change the ENSO amplitude. Mixed layer heat budget analysis for the CTRL and Pclim reveals that precipitation anomaly enhances the ENSO variability through modifying oceanic "vertical processes," such as the entrainment.

