Influence of the Interdecadal Pacific Oscillation on South Asian and East Asian summer monsoon rainfall in CMIP6 models

The present study investigates the influence of the Interdecadal Pacific Oscillation (IPO) on the South Asian and East Asian summer monsoon rainfall and associated ocean-atmospheric conditions in 24 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. The observations illustrate significant negative precipitation anomalies over the Central India and Central China (CICC) regions in response to positive IPO during the summer season. Almost two-thirds of the models could well represent the IPO pattern as in observations with strong sea surface temperature (SST) warming in the central to eastern Pacific and cooling in the north and south-central Pacific. CMIP6 models are classified into two groups based on the area-averaged regression of precipitation over the CICC region. Models in group 1 (G1), representation of IPO–CICC teleconnections, are somewhat similar to the observations, while in group 2 (G2), models underestimate the IPO–CICC relationship. Low-level anomalous anticyclonic circulation anomalies and moisture divergence contribute to precipitation reduction in observations and G1 models over the CICC region. In addition, the large-scale divergence at the lower level, along with the high-level convergence across the CICC region, corresponding to IPO, is as strong in the G1 models as in the observations. However, G2 models are not able to represent these circulation patterns and therefore not able to represent the IPO–CICC teleconnections well. Overall, G1 models can represent large-scale air-sea interactions across the Indo-Pacific region associated with an IPO. This study highlights the importance of capturing/simulating the reliable large-scale circulation patterns related to IPO in coupled models to capture the IPO–CICC teleconnections.