HR: 1340h
AN: A23C-0814    [Abstracts]
TI: A new Idealized Global Climate Model and its Application to Dust-Climate Interactions
AU: * Shell, K M
EM: kshell@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, Mail Code 0224 9500 Gilman Drive, La Jolla, CA 92093-0224
AU: Somerville, R
EM: rsomerville@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, Mail Code 0224 9500 Gilman Drive, La Jolla, CA 92093-0224
AB: Airborne mineral dust can influence the climate by altering the radiative properties of the atmosphere. However, the sign and magnitude of climate forcing and response are not well known. An idealized global model is developed to study processes and feedbacks within the dust-climate system. The model is solved numerically for equilibrium climate states defined by zonal average surface and atmospheric temperatures as a function of latitude. Radiative, latent, and sensible heating are parameterized. The model includes a variable lapse rate, based on moist convection in the tropics and baroclinic eddies in high latitudes, and parameterizations of the major dynamical mechanisms responsible for meridional heat transport: the Hadley cell, midlatitude baroclinic eddies, and ocean circulation. The model determines the longwave and shortwave dust forcing, as well as the resulting climate change, based on the specified dust distribution and optical properties. The model reproduces both the observed mean variation of temperature with latitude and the global average heat budget. The model also produces realistic radiative forcing values for the present day dust distribution. Modeled radiative, temperature, and hydrological changes caused by the Mount Pinatubo eruption compare favorably to observations and general circulation model results. For a reference set of dust optical properties, the modeled global average top-of-atmosphere (TOA) shortwave dust forcing is -0.73 W/m$^2$, and the longwave forcing is 0.23 W/m$^2$. For plausible ranges in dust optical properties, the net forcing varies from -2.0 W/m$^2$ to +3.1 W/m$^2$. Studies which use a shortwave single scattering albedo corresponding to World Climate Program dust optical properties may be underestimating the effect of dust. Dust decreases the surface and atmospheric temperatures by about 0.1 K and reduces latent and sensible heat fluxes by 1%. Based on the range of optical property values used, the surface temperature change ranges from -0.3 K to 0.6 K. The latent heat change ranges from -1.9 W/m$^2$ to 0.5 W/m$^2$. In addition, temporal variations in dust concentration contribute to interannual climate variability.
DE: 3359 Radiative processes
DE: 3367 Theoretical modeling
DE: 1620 Climate dynamics (3309)
DE: 0305 Aerosols and particles (0345, 4801)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting