Change in the Tropical Hadley Cell Since 1950

Abstract

The change in the tropical Hadley cell since 1950 is examined within the context of the long-term warming in the global surface temperatures. The study involves analyses of observations, including various metrics of Hadley cell, and ensemble 50-year simulations by an atmospheric general circulation model forced with the observed evolution of global sea surface temperature since 1950. Consistent evidence is found for an intensification of the Northern Hemisphere winter Hadley cell since 1950. This is shown to be an atmospheric response to the observed tropical ocean warming trend, together with an intensification in El Niño’s interannual fluctuations including larger amplitude and increased frequency after 1976. The intensification of the winter Hadley cell is shown to be associated with an intensified hydrological cycle consisting of increased equatorial oceanic rainfall, and a general drying of tropical/subtropical landmasses. This Hadley cell change is consistent with previously documented dynamic changes in the extratropics, including a strengthening of westerly atmospheric flow and an intensification of midlatitude cyclones.