Observational Evidence for Poleward Expansion of the Hadley Circulation

How the Hadley circulation changes in response to global climate change and how its change impacts upon regional and global climates has generated a lot of interest in the literature in the past few years. In this paper, consistent and statistically significant poleward expansion of the Hadley circulation in the past few decades is demonstrated, using independent observational datasets as proxy measures of the Hadley circulation. Both observational outgoing longwave radiation and precipitation datasets show an annual average total poleward expansion of the Hadley cells of about 3.6o latitude. Sea level pressure from observational and reanalysisdatasets show smaller magnitudes of poleward expansion, of about 1.2o latitude. Ensemble general circulation model simulations forced by observed time-varying sea surface temperatures were found to generate a total poleward expansion of about 1.23o latitude. Possible mechanisms behind the changes in the horizontal extent of the Hadley circulation are discussed.