The Dynamics of the Hadley Circulation and its Response to a Wide Range of Climate Changes: From a Hierarchy of Models to New Theories

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This grant will fund research on the Hadley cell, an overturning atmospheric circulation with rising motion in the rainy regions near the equator and subsiding motions over the subtropics on either side of the equator. The Hadley cell is quite important for the climate of the tropics and subtropics, as regions under the subsiding branches of the circulation are characterized by arid or semi-arid climates. The research addresses the behavior of the Hadley cell, including its width, strength, and the central latitude of the rising motions, under a variety of simulated planetary climate states. The project has three main objectives: 1) To determine how the Hadley circulation changes over a wide range of climates, in order to place possible past, present, and future changes in a larger context. The research will determine, for example, whether the Hadley circulation generally widens as the climate warms, even in climates very different from the present. 2) To determine how the Hadley circulation responds to climate changes in climate simulations of increasing complexity, including simulations in which the world's surface is entirely ocean with no landmasses, ocean-only simulations including sea ice, and configurations with idealized continents. These simulations are intended to identify mechanisms through which the Hadley cell is influenced by external factors such the insolation changes associated with the ice age cycles. 3) To develop scientific theories that account for observed and simulated changes of the Hadley circulation.The issue of Hadley cell change in a warming climate has societal impacts, as observations and simulations suggest that the Northern and Southern Hemisphere Hadley cells may be widening due to global warming, which could result in aridification in some regions. In addition, the work will promote the education and training of the next generation of scientists by funding a postdoctoral scholar, two graduate students, and two summer undergraduate research fellows.