HR: 10:35h
AN: A22B-02    [Abstracts]
TI: Sensitivity of tropical circulation and ITCZ to the underlying meridional gradient of SST
AU: * Dunkerton, T J
EM: tim@nwra.com
AF: NorthWest Research Associates, 14508 NE 20th St, Bellevue, WA 98007-3713, United States
AU: Borth, H
EM: borth@uni-mainz.de
AF: Institute for Atmospheric Physics, Becherweg 21, University of Mainz, Mainz, 55099, Germany
AU: Wirth, V
EM: vwirth@uni-mainz.de
AF: Institute for Atmospheric Physics, Becherweg 21, University of Mainz, Mainz, 55099, Germany
AB: The meridional gradient of sea surface temperature (SST) plays an important role in setting the location of the Intertropical Convergence Zone (ITCZ) and the properties of its associated meteorological phenomena such as easterly waves, equatorially trapped waves, Hadley circulation, and tropical cyclones. The ability of the SST distribution to dictate these properties depends on the strength of its meridional gradient: a stronger gradient implies greater control of atmospheric phenomena and vice versa. Owing to the distribution of land and ocean, the present climate of Earth displays a wide range of ITCZ properties depending on longitude, as well as interannual variability such as ENSO. In certain regions, such as the Atlantic and east/central Pacific, the underlying meridional gradient of SST plays a larger role than elsewhere, and it is possible to investigate aspects of this control using an aquaplanet GCM in which longitudinal variations of externals are ignored completely. This talk will explore the role of SST meridional curvature in setting the location of the ITCZ and the meridional extent of the Hadley circulation. The number of ITCZs (one or two) is shown to depend on the SST gradient, and in an intermediate range of parameter space, both regimes are supported; a hysteresis is observed between these two states as the gradient of SST is varied slowly in time. The properties of waves and their role in spawning hurricanes in the idealized model is also discussed. It is thought that certain paleoclimatic regimes have witnessed a fundamental though transient change in ITCZ behavior resulting from changes in equator-to-pole temperature gradient. Although near-term projections of future climate change involve a smaller alteration of ITCZ properties, these changes may nevertheless be important to tropical meteorology and the impact of extreme events such as hurricanes. This will be shown explicitly using results from the idealized aquaplanet model. The behavior of the numerical model follows reasonably well the predictions of a simple theoretical model of the nonlinear angular-momentum conserving Hadley circulation.
DE: 1620 Climate dynamics (0429, 3309)
DE: 3319 General circulation (1223)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting