Regional Perspective of Hadley Circulation and Its Uncertainties Among Different Datasets: Spread in Reanalysis Datasets

The Hadley circulation (HC) is often considered zonally uniform and defined using the zonally averaged mass stream function (MSF). However, the longitudinal distribution of the overturning circulation is far from uniform, which has profound impacts on regional climates. This study uses a recently developed technique to examine the three-dimensional MSF and thus the regional manifestations of the HC, and evaluates their climatology and seasonality in eight commonly used reanalysis datasets. This comparison emphasizes the spatial structure and the intensity of four regional Hadley cells, defined based on the natural boundaries of the three-dimensional MSF. Specifically, two Hadley cells are located in the Indo-Pacific warm pool region, with a strong and relatively deep cell extending from the equator to mid-latitudes in each hemisphere. The other two cells are located over the East Pacific-Atlantic sector, which is relatively weak and shallow, confined within the tropics and subtropics. The spatial structure of each regional cell is nearly identical among all reanalysis datasets, with pairwise spatial correlation coefficients higher than 0.9. However, the intensities of regional MSF show a large spread among these datasets. The range of this spread reaches up to about half of the means of all reanalysis datasets over the Indo-Pacific warm pool region in the Northern Hemisphere. Further analysis reveals a large spread in the spatial structure and the amplitudes of the regional HC trends among different reanalyses. The findings highlight uncertainties in the regional circulation of modern reanalysis datasets and have implications for interpreting past and future circulation changes.