On the discrepancies in the changes in the annual mean Hadley circulation among different regions and between CMIP5 models and reanalyses

Recent studies have investigated past and future changes in the intensity and sinking branch of the global zonally averaged Hadley circulation (ZAHC), and discrepancies were found between climate models and reanalyses. However, studies concerning the regional Hadley circulation (HC), especially based on model simulations, are relatively rare. Here, using reanalyses and CMIP5 simulation datasets, we study the long-term changes in regional HCs over Africa (AFHC), the Indian Ocean (IOHC), the western Pacific (WPHC), the eastern Pacific (EPHC), South America (SAHC), and the Atlantic (ATHC). The results obtained from the reanalyses show that during the historical period, the intensification of the WPHC, EPHC, SAHC, and ATHC in the Northern Hemisphere (NH) may contribute to the strengthening of the ZAHC in the NH, while the contributions of the NH AFHC and IOHC are relatively small. The intensification of the IOHC, EPHC, SAHC, and ATHC in the Southern Hemisphere (SH) may contribute to the strengthening of the ZAHC in the SH, while the contributions of the SH AFHC and WPHC are negative. Regarding the poleward edge, the NH HCs have generally shifted poleward in recent decades, while trends in the SH HCs are nonsignificantly greater than zero in most cases. As reanalysis trends in the HC fall within the range of the model trends, we do not find sufficient evidence to demonstrate a discrepancy in the long-term changes in the HC between the CMIP5 models and reanalyses. The correlations of the HC intensities (poleward edges) among different regions obtained from the reanalysis data are generally different than (similar to) those obtained from the CMIP5 historical simulations, and the difference (similarity) may be caused by the difference (similarity) in the internal variabilities between the reanalyses and CMIP5 preindustrial control simulations. The changes in these HCs under global warming conditions are also investigated in this study.