Group seminar on 16. February, 14:15 CET

This seminar presents the changes in the strength of Hadley circulation (HC) in ERA5 reanalysis in the recent decades (1979-2018). To assess the trends in HC strength in reanalyses we employ a more detailed analysis of Kuo-Eliassen equation, and test HC relationship with interannual-to-decadal variability. ERA5 reanalysis shows that the mean streamfunction of the northern and southern Hadley cell has been strengthening, especially in the winter and spring. However, a steady decline of northern HC strength is observed after 2002. Most of the HC trend and variability is explained by the meridional gradient of diabatic heating. We show that the meridional gradient of precipitation and the strength of HC in ERA5 verify well with an observational precipitation dataset (GPCP), suggesting that trends in this reanalysis are not an artefact of the misrepresentation of latent heating. Instead, using ERA5 preliminary data for 1950-1978, we show that the changes in HC strength are likely a consequence of multidecadal variability (AMO) that affects Walker circulation, and related frictional and diabatic processes, which in turn drive HC variability. This work has implications for further understanding of the long-term variability of the HC.