| Summary: | The fake below-ground meridional wind (FBGMW) exists in reanalysis products which is not present in the real atmosphere and should be removed before calculating the mass stream function (MSF). In this study, the impacts of FBGMW on Hadley circulation (HC) in terms of climatology, interannual variability, and long-term trends were investigated using five reanalysis data sets based on three different computing methods. Generally, the impacts of FBGMW on the HC are most notable, although the absolute magnitude of the FBGMW is rather small. The key finding of this study is that the FBGMW has vital influences on the Northern Hemisphere (NH) HC during boreal summer. This is because the NH HC during boreal summer is very weak; the errors of the MSF caused by not considering FBGMW have more obvious influences on the NH HC during boreal summer than that in other months. The previous analysis without considering FBGMW led to overestimation of the poleward expansion of the NH HC during boreal summer, and the long-term trends of the HC should be more accurately estimated after considering the FBGMW. This finding suggests that the previous studies related to the NH HC during boreal summer without considering FBGMW should be reconsidered.
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