1631 / 2019-08-23 16:11:39

Uncertainty in the future projections of Pacific-Indian Ocean air-sea coupled modes: the role of internal variability

9、大气科学与全球变化 > 专题6：区域气候变化动力学

El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) are the main air-sea coupled modes in the tropical Pacific and Indian Ocean, influencing the global climate system. The response of these modes to global warming are quite uncertain among climate models. In this study, the uncertainty in the future projections of ENSO and IOD under global warming, especially that resulting from internal variability, are investigated based on a 40-member ensemble from the Community Earth System Model Large Ensemble (CESM-LE) project. For the ENSO (IOD) amplitude change, the inter-member uncertainty in CESM-LE is about 80% (50%) of the intermodel uncertainty in the phase 5 of the Coupled Model Intercompatison Project (CMIP5) multimodel ensemble, indicating the important role of internal variability in the ENSO (IOD) future projection.
In CESM-LE, the inter-member diversity of ENSO amplitude change is associated with a zonal dipole pattern of sea surface temperature (SST) mean state warming in the tropical Pacific Ocean. While in the Indian Ocean, the inter-member diversity of IOD amplitude change is not correlated with that of mean state change, due to complex changes in oceanic and atmospheric feedbacks. Instead, the ensemble spread in IOD amplitude change is correlated with that in ENSO amplitude change in CESM-LE, reflecting the close inter-basin relationship between the tropical Pacific and Indian Ocean in this model. This study also indicates that a large ensemble of ~15 members is needed to detect a significant change in ENSO amplitude and suppress the interference of internal variability in CESM-LE.