Role of Atlantic Air–Sea Coupling in the Effect of the Tibetan Plateau Heating on the Upstream Climate over Afro–Eurasia–Atlantic Regions

Previous studies have demonstrated that in boreal summer atmospheric diabatic heating over the Tibetan Plateau (TP) exerts significant influences on the “upstream” climate of the Atlantic-African-European sector, including the Atlantic subtropical high and Sahel rainfall. Through several sensitivity experiments using the NCAR Community Earth System Model, this study demonstrates that the air-sea interaction over the Atlantic Ocean significantly modulates the above TP impact on the “upstream” climate.

Compared with the experiments with fixed climatological sea surface temperature (SST) annual cycle in the Atlantic basin, remarkable changes are found in the climate anomalies that are related to the strengthened TP thermal forcing in the current experiment with air-sea interaction over the Atlantic. In particular, the changes in meridional SST and air temperature gradients over the North Atlantic enhance the northern portions of the TP-induced tropospheric anticyclones and reduce the precipitation over the northwestern Atlantic. The precipitation reduction is accompanied by a wave train pattern with north-northeastward downstream influences, including three positive centers over the North Atlantic, the Arctic Ocean, and east of Japan, as well as four negative centers over northeastern North America, North Europe, the mid-Atlantic, and the northwestern Pacific. Due to the easterly wind anomalies over the tropical Atlantic and West Africa associated a weakened thermal low, anomalous convergence (divergence) occurs over the tropical western (eastern) Atlantic, leading to an increase in precipitation over the tropical western Atlantic and a weakening of precipitation dipole related to TP over the tropical eastern Atlantic and West Africa. Overall, the modulation of Atlantic air-sea interaction accounts for 20-50 percent of the upstream climate signals induced by the TP thermal effect.