The sea surface temperature anomalies (SSTAs) over the north tropical Atlantic (NTA) in spring are positively correlated with the subsequent summer SSTAs over the north Indian Ocean (NIO). We find that this NTA-NIO connection experienced a decadal weakening around the early-2000s. Before that, the warming in NTA leads to significant positive NIO SSTAs via tropospheric temperature mechanism and wind-evaporation-SST feedback, being consistent with previous studies. Nevertheless, after the early-2000s, the positive NTA SSTAs in spring could efficiently trigger negative SSTAs over the central and eastern tropical Pacific in the following seasons, in contrast to the weak response in the tropical Pacific to the NTA before the early-2000s. The negative SSTAs in the central and eastern tropical Pacific induce negative SSTAs over the NIO, which offsets the influence of the NTA on the NIO and leads to a weakened NTA-NIO connection. Additionally, the decadal variation in the NTA-tropical Pacific connection, as well as the NTA-NIO connection, tends to be linked to the decadal change in climatological SST over the tropics. The NTA SST warms faster relative to the central and eastern tropical Pacific, which increases the Atlantic-Pacific SST gradient and thus intensifies the response of tropical Pacific to the NTA, and in turn leads to the weakened NTA-NIO connection. Both observations and the Coupled Model Intercomparison Project Phase 6 (CMIP6) preindustrial control simulations support the results above and highlight the importance of trans-basin interactions among tropical oceans to the variation of NIO originating from the NTA.

Atlantic Ocean,Indian Ocean,ENSO,Decadal variability,Transbasin interactions