Increasing connections of the leading internal mode of the summertime Northwest Pacific subtropical anticyclone with preceding ENSO under greenhouse warming in FGOALS‐g3 super‐large ensemble

Abstract

AbstractWhile much progress has been made in understanding how anthropogenic forcing influences the climate mean state, less attention has been paid to how it may modulate the internal variability of air–sea coupled mode. This study investigates forced changes of the leading internal mode of the summertime Northwest Pacific subtropical anticyclone (NWPSA) and the related sea surface temperature (SST) anomalies based on the 110‐member FGOALS‐g3 super‐large ensemble for the period of 1850–2099. The leading internal mode of the NWPSA variability is obtained by applying snapshot‐empirical orthogonal function analyses across the ensemble dimension each year. It is shown that the connection between the NWPSA and the preceding El Niño–Southern Oscillation (ENSO) strengthens in response to anthropogenic forcing, and the precipitation along the northwestern flank of the NWPSA increases correspondingly due to stronger water vapour transport. The SST anomalies corresponding to the change invoke a rapid transition from El Niño to La Niña in a warming world, which induces a zonal SST contrast between the Indian Ocean warming and the equatorial Pacific cooling, favouring a strengthening of the NWPSA. The stronger influence of ENSO on the NWPSA in the ensuing summer under greenhouse warming may result from the pronounced increase in the internal variability of the central deep‐equatorial Pacific SST and precipitation over the western‐central equatorial Pacific in winter. The stronger influence indicates that ENSO may serve as a stronger predictor of the summertime NWPSA in a warming climate, and may improve the skills of the seasonal forecast of the climate over East and South Asia in summer.