Interhemispheric Thermal Gradients and Multidecadal Variations in the Tropical Climate over the 20th Century


John Chiang

15:55:00 - 16:45:00

101 , Mathematics Research Center Building (ori. New Math. Bldg.)

Several lines of evidence – paleoclimate observations, model simulations, and theory - suggest that cooling originating over the northern extratropics have a profound effect on tropical rainfall, by generating an interhemispheric thermal gradient that shifts the latitudinal position of the Intertropical Convergence Zone southward, and weaken rainfall over Northern Hemisphere summer monsoon regions. This change is associated with an altered cross-equatorial atmospheric energy transport induced by hemispheric differences in surface and top-of-atmosphere energy flux. In this talk, I highlight a few cases where this framework may be usefully applied to understanding multidecadal and longer-timescale forced changes in tropical rainfall over the 20th century, focusing on two cases: a southward trend in the tropical Atlantic ITCZ, and the late 1960’s abrupt weakening in the North African and Asian monsoons.

For material related to this talk, click here.