Inter-model robustness of the forced change of the ENSO-Indian Summer Monsoon Teleconnection

Abstract

Concerning the robustness of predicting the forced response of the El Niño—Southern Oscillation-Indian summer monsoon (ENSO-ISM) teleconnection based on 9 CMIP-class models, we come to distinguish three time periods. (1) In the late 20th century, the trend was insignificant in most models, which does not permit a statement on robustness in this period. Thus the weakening of the teleconnection reported from the observational data might not be truly forced. (2) Furthermore, we find it typical that under global warming in the first part of the 21st century, the teleconnection is strengthening or non-decreasing. This considerable inter-model robustness is owed to an increasing ENSO variability as well as coupling strength. (3) At the end of the 21st century, however, under strong forcing, the teleconnection change is not robustly modeled: the ENSO variability change is not projected robustly across models, either with respect to the start or the rate of the ENSO variance decline, competing this time with an increase of the coupling strength. The difference in the projected coupling coefficient between models is mainly attributed to the disagreement in the projected ENSO-induced changes in the regional Hadley cell and SST patterns over the ISM domain, despite the agreement on the projected eastward shift of the Walker cell over the Pacific Ocean.