Attribution of the Southern Hemisphere Hadley cell widening

Abstract:

It has been suggested that the Hadley cell has been widening during the past three decades in both hemispheres, but attribution of its cause(s) remains challenging. By applying an optimal fingerprinting technique to available modern reanalyses observations and multiple coupled climate models participating in the CMIP3 and CMIP5, we detect an influence of human-induced stratospheric ozone depletion on the observed expansion of the Hadley cell in the Southern Hemisphere (SH) summer. The detected signal is found to be separable from other external forcings that include greenhouse gases, confirming a dominant role of stratospheric ozone in the SH-summer climate change. Our results are largely insensitive to observational and model uncertainties, providing additional evidence for a human contribution to the atmospheric circulation changes. Possible attribution of local Hadley cell expansion will be discussed.