HR: 08:03h
AN: A31C-01 INVITED    [Abstracts]
TI: Radiative Transfer in a Climate GCM: Or how to Optimize, Maximize, and Blend Computational Speed, Accuracy, Physical Realism, and Diagnostic Capability of Radiative Transfer Calculations
AU: * Lacis, A A
EM: alacis@giss.nasa.gov
AF: NASA-GISS, 2880 Broadway, New York, NY 10025, United States
AB: Climate modeling is a computational effort in deciphering a boundary value problem in physics. Absorbed solar radiation is the energy input to the Earth-atmosphere system, while thermal radiation emitted to space is the sink. Global energy balance, modulated by clouds, aerosols, absorbing gases, atmospheric and ocean heat transports, and their interacting heat capacities, produces the prevailing climate at the Earth's surface. Radiative heating and cooling determines the atmospheric temperature distributions which in turn provide the ultimate driving force behind atmospheric motions. The physics of radiative transfer is well understood, so that in principle, accurate heating and cooling rates could be calculated for any specified state of the atmosphere. The task of the GCM radiative transfer model is to perform these calculations fast enough to be practical in climate simulations, while retaining as much of the attainable accuracy as possible. For tractability, the physical realism of the model atmosphere is described in terms of idealized plane-parallel geometry. The GCM radiation model also provides diagnostic information by means of which the GCM performance can be evaluated against available observations. These objectives can be achieved using the correlated k-distribution for modeling thermal radiation, and the single gauss point doubling/adding for modeling solar radiation. Results show that CO2 is the principle non-condensable core-component of the terrestrial greenhouse, accounting for about 20 per cent of the total (33 K) terrestrial greenhouse effect, while the principal feedback components, water vapor and clouds, account for about 50 and 25 per cent, respectively. In the context of current climate, doubled CO2 by itself increases the terrestrial greenhouse by 1.2 K, while feedback contributions, due primarily to water vapor, add an additional 1.5 K.
DE: 0360 Radiation: transmission and scattering
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting