Uncertainties of ENSO-related Regional Hadley Circulation Anomalies within Eight Reanalysis Datasets

El Nino-Southern Oscillation (ENSO), the leading mode of global interannual variability, usually intensifies the Hadley Circulation (HC), and meanwhile constrains its meridional extension, leading to an equatorward movement of the jet system. Previous studies have investigated the response of HC to ENSO events using different reanalysis datasets and evaluated their capability in capturing the main features of ENSO-associated HC anomalies. However, these studies mainly focused on the global HC, represented by a zonal-mean mass stream function (MSF). Comparatively fewer studies have evaluated HC responses from a regional perspective, partly due to the prerequisite of the Stokes MSF, which prevents us from integrating a regional HC. In this study, we adopt a recently developed technique to construct the three-dimensional structure of HC and evaluate the capability of eight state-of-the-art reanalyses in reproducing the regional HC response to ENSO events. Results show that all eight reanalyses reproduce the spatial structure of HC responses well, with an intensified HC around the central-eastern Pacific but weakened circulations around the Indo-Pacific warm pool and tropical Atlantic. The spatial correlation coefficient of the three-dimensional HC anomalies among the different datasets is always larger than 0.93. However, these datasets may not capture the amplitudes of the HC responses well. This uncertainty is especially large for ENSO-associated equatorially asymmetric HC anomalies, with the maximum amplitude in Climate Forecast System Reanalysis (CFSR) being about 2.7 times the minimum value in the Twentieth Century Reanalysis (20CR). One should be careful when using reanalysis data to evaluate the intensity of ENSO-associated HC anomalies.

Automated summary

El Nino-Southern Oscillation (ENSO) usually intensifies the Hadley Circulation (HC) and restricts its meridional extension, leading to an equatorward movement of the jet system. This study evaluates the capability of eight reanalysis datasets in reproducing the regional HC response to ENSO events using a newly developed three-dimensional HC structure technique. Results show that while these datasets reproduce the spatial structure of HC responses well, they may not capture the amplitudes of the HC responses accurately, especially for ENSO-associated equatorially asymmetric HC anomalies.