HR: 12:05h
AN: A12C-08    [Abstracts]
TI: The Dry Hadley Cell
AU: * Mitchell, J L
EM: lloyd1@uchicago.edu
AF: Department of Geophysical Sciences, University of Chicago, 5734 S. Ellis Ave., Chicago, IL 60637 United States
AU: Caballero, R
EM: rca@geosci.uchicago.edu
AF: Mathematical Physics Department, University College Dublin, UCD, Belfield, Dublin, 4 Ireland
AU: Pierrehumbert, R T
EM: rtp1@geosci.uchicago.edu
AF: Department of Geophysical Sciences, University of Chicago, 5734 S. Ellis Ave., Chicago, IL 60637 United States
AB: In atmospheres with a condensible component, there is an intrinsic asymmetry between ascending motion, which follows a moist adiabiat, and subsidence which---in the absence of other processes---would follow a dry adiabat. This asymmetry allows the Hadley cell to transport vast amounts of heat poleward, wiping out temperature gradients in the tropics. But what if there is no condensible component? For instance, the atmosphere during a ``snowball'' glaciation would have been very cold and dry. Additionally, the present tropical Martian climate is dry, as may be the case in a number of extrasolar planets being discovered. We present results from an axisymmetric model of a dry atmosphere with idealized forcing (gray-gas radiation and dry convective adjustment) and compare these with an extension of existing theory that predicts the scaling of the width and strength of the Hadley cell with Rossby number. We find that at low Rossby number, the width of the cell behaves much like it did in the moist case, but the strength does not. We attribute this discrepancy to the mechanism that sets the stability; since dry convection restores the atmosphere to neutral stability, the circulation itself is responsible for any residual stability, whereas moist convection sets the stability in the modern tropical atmosphere.
DE: 0545 Modeling (4255)
DE: 3319 General circulation (1223)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005