Recent and future changes in the Asian monsoon‐ENSO relationship: Natural or forced?

Abstract

AbstractThe Asian monsoon‐ENSO (El Niño–Southern Oscillation) relationship in the 20th and 21st centuries is examined using observations and Coupled Model Intercomparison Project Phase 5 (CMIP5) model simulations. CMIP5 models can simulate the ENSO‐monsoon spatial structure reasonably well when using the multimodel mean. Running correlations show prominent decadal variability of the ENSO‐monsoon relationship in observations. The modeled ENSO‐monsoon relation shows large intermodel spread, indicating large variations across the model ensemble. The anthropogenically forced component of ENSO‐monsoon relationship is separated from the naturally varying component based on a signal‐to‐noise maximizing empirical orthogonal function analysis using global sea surface temperature (SST). Results show that natural variability plays a dominant role in the varied ENSO‐monsoon relationship during the 20th century. In the 21st century, the forced component is dominated by enhanced monsoon rainfall associated with SST warming, which may contribute to a slightly weakened ENSO‐monsoon relation in the future.