Biography
Biography: Jie He
Abstract
The subtropics encompass many of the world’s driest regions and climate models robustly predict a large-scale decline in subtropical precipitation from anthropogenic forcing. This projection has become popularly related to the “dry-get-drier” paradigm. The expectation that climate change will generally exacerbate the rainfall deficiency of the subtropical regions has excited great concerns. On the other hand, some studies have attributed the subtropical precipitation decline to the poleward expansion of the Hadley cell. In this talk, I will show that neither the “dry-get-drier” nor poleward expansion mechanism is relevant to the large-scale subtropical precipitation decline. It is found that the subtropical precipitation decline forms primarily from the fast adjustment to CO2 forcing in which neither of the two proposed mechanisms exist. Permitting the increase in moisture and the Hadley cell expansion does not substantially change the characteristics of the large-scale subtropical precipitation decline. This precipitation change should be interpreted as a response to the land-sea warming contrast, direct radiative forcing of CO2 and in certain regions, pattern of SST changes. In addition, a careful examination of the spatial patterns of the projected precipitation change shows that the subtropical precipitation decline is primarily located over ocean. Over subtropical land regions, the precipitation decline is muted or even reversed by the land-sea warming contrast.