Investigating dynamical mechanisms behind tropical widening
Tuesday, July 28, 2015: 10:40 AM
Paul Staten, Indiana University Bloomington, Geological Sciences, Bloomington, IN, United States, Thomas Reichler, University of Utah, Salt Lake City, UT, United States and Jian Lu, Pacific Northwest National Laboratory, Richland, WA, United States
Abstract:
The recent widening of the Hadley circulation, though largely reproducible in climate simulations, is not well understood. To study the underlying mechanisms, we apply idealized, instantaneous forcings in a realistic atmospheric general circulation model (GFDL AM2.1). The prescribed forcings include greenhouse gas increases, stratospheric ozone depletion, and sea surface warming. This blend of idealized forcings and comprehensive model physics allows us to discriminate between several hypothesized mechanisms behind the poleward shifts in the midlatitude jet, and of the Hadley cell. Overall, the width of the Hadley cell follows closely the poleward shift of the midlatitude jets, which in turn appear to respond to changing wave reflection mechanism recently posited by David J. Lorenz (2014). The increase in wave breaking equatorward of the midlatitude jet not only results in a poleward-shifted jet, but it also delays the onset of baroclinic instability in poleward moving air in the upper branch of each cell.
