Interdecadal Variations in ENSO Influences on Northwest Pacific-East Asian Early Summertime Climate Simulated in CMIP5 Models

The present study investigates interdecadal modulations of the El Nino-Southern Oscillation (ENSO) influence on the climate of the northwest Pacific (NWP) and East Asia (EA) in early boreal summer following a winter ENSO event, based on 19 simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In the historical run, 8 out of 19 models capture a realistic relationship between ENSO and NWP early summer climate-an anomalous anticyclone develops over the NWP following a winter El Nino event- and the interdecadal modulations of this correlation. During periods when the association between ENSO and NWP early summer climate is strong, ENSO variance and ENSO-induced anomalies of summer sea surface temperature (SST) and tropospheric temperature over the tropical Indian Ocean (TIO) all strengthen relative to periods when the association is weak. In future projections with representative concentration pathways 4.5 and 8.5, the response of TIO SST, tropospheric temperature, and NWP anomalous anticyclone to ENSO all strengthen regardless of ENSO amplitude change. In a warmer climate, low-level specific humidity response to interannual SST variability strengthens following the Clausius-Clapeyron equation. The resultant intensification of tropospheric temperature response to interannual TIO warming is suggested as the mechanism for the strengthened ENSO effect on NWP-EA summer climate.