HR: 0830h
AN: PP21B-1167    [PDF]
TI: Water vapour, atmospheric dynamics and the greenhouse effect
AU: * Caballero, R
EM: rca@geosci.uchicago.edu
AF: Department of the Geophysical Sciences, Universtity of Chicago, 5734 S Ellis Av, Chicago, IL 60637 United States
AU: Huber, M
EM: huberm@purdue.edu
AF: Department of Earth and Atmospheric Sciences, Purdue University, 1397 Civil Engineering Bldg, West Lafayette, IN 47906 United States
AU: Pierrehumbert, R
EM: rpt1@geosci.uchicago.edu
AF: Department of the Geophysical Sciences, Universtity of Chicago, 5734 S Ellis Av, Chicago, IL 60637 United States
AB: Unlike other greenhouse gases, water vapour concentration is not limited by availability (given the infinite source in the oceans) but by saturation vapour pressure, which increases exponentially with temperature. The resulting positive ``water vapour feedback'' acts as a strong amplifier of climate change. Just how strong the amplification is, however, depends on a host of mechanisms in which dynamics play a key role. Atmospheric moisture decreases roughly exponential with height, and vertical motion induced by horizontal temperature gradients will therefore moisten ascending regions and dry out subsiding ones. Vertical motion also affects moist convection, an important source of atmospheric moisture. Over Earth's history, changes in mean temperature have generally been accompanied by changes in gradients. Understanding the evolution of Earth's greenhouse effect therefore requires a detailed understanding of how atmospheric dynamics reinforces or counteracts water vapour feedback. We will discuss possible mechanisms using a hierarchy of models, including a two-column, ENSO-resolving model to investigate interactions in the equatorial zone, and a 3D atmospheric model coupled to a slab ocean to explore the response of the Hadley cell to changes in the Walker circulation and to study the extratropical regime, where vertical motion is mainly due to the ageostrophic component of baroclinic eddies. Finally, we assess the relevance of these mechanisms by comparing fully-coupled simulations of modern and Eocene climates, using NCAR's CCSM.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 3300 METEOROLOGY AND ATMOSPHERIC DYNAMICS
DE: 9600 INFORMATION RELATED TO GEOLOGIC TIME
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting