Observational Evidence for Poleward Expansion of the Hadley Circulation

How the Hadley circulation changes in response to global climate change and how its change impactsupon regional and global climates has generated a lot of interest in the literature in the past few years. Inthis paper, consistent and statistically significant poleward expansion of the Hadley circulation in the pastfew 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 polewardexpansion of the Hadley cells of about 3.6^o latitude. Sea level pressure from observational and reanalysisdatasets show smaller magnitudes of poleward expansion, of about 1.2^o latitude. Ensemble general circulation model simulations forced by observed time-varying sea surface temperatures were found to generate a total polewardexpansion of about 1.23^o latitude. Possible mechanisms behind the changes in the horizontal extent of theHadley circulation are discussed.