The Hadley Circulation's Response to Imposed Idealized Ocean Heat Transport in an Aquaplanet GCM
Abstract
This study seeks to further theoretical understanding of Hadley circulation (HC) width and the mechanisms governing HC expansion by exploring the response of a zonally-symmetric slab-ocean aquaplanet general circulation model to imposed poleward ocean heat transport (OHT). Previous work has shown that simulations with some representation of poleward OHT exhibit wider HCs than those without; however, the precise mechanism by which OHT causes the HC to widen remains unexplained. Here, we propose a HC expansion mechanism involving a change to the seasonal migration of the intertropical convergence zone (ITCZ). By pushing the ITCZ further from the equator during the annual cycle, OHT decreases the "moment arm" of the ITCZ with respect to Earth's axis of rotation, thereby decreasing the angular momentum input into the HC. Subsequently, at any given latitude, the zonal wind in the upper branch of the HC is reduced, pushing the latitude at which the HC becomes baroclinically unstable poleward and causing the HC to expand. Given that many previous studies have focused on the role of changes to subtropical static stability or subtropical wave breaking in driving HC expansion, this study represents an important addition to the HC expansion literature. Finally, although this proposed ITCZ latitude-driven expansion mechanism can explain a substantial portion of the total HC widening in simulations with a seasonal cycle, OHT does cause (reduced) HC expansion in simulations in which annual-mean insolation is imposed, suggesting the existence of a second HC expansion mechanism to be identified in future work.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.A51O..08H
- Keywords:
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- 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES;
- 3319 General circulation;
- ATMOSPHERIC PROCESSES;
- 3373 Tropical dynamics;
- ATMOSPHERIC PROCESSES;
- 1620 Climate dynamics;
- GLOBAL CHANGE