HR: 09:45h
AN: C31B-08    [Abstracts]
TI: The Influence of Cloud and Surface Properties on the Arctic Shortwave Radiation Budget in IPCC Coupled Model Simulations
AU: * Gorodetskaya, I V
EM: irina@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Tremblay, B
EM: tremblay@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Liepert, B
EM: liepert@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Cullather, R I
EM: cullat@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Cane, M A
EM: mcane@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: We analyze the impact of the Arctic sea ice concentrations, surface albedo, cloud amounts and cloud water content on the shortwave radiation budget at the surface and the top of atmosphere in the 20th century simulations of three coupled models participating in the IPCC 4th Assessment Report. The models are: Goddard Institute for Space Studies (GISS) ModelE, UK Met Office Hadley Centre Model (UKMO HadCM3), and National Center for Atmosphere Research Climate Community System Model (NCAR CCSM3). The modeled parameters over the Arctic Ocean during the 1959-1998 time period are compared to the observations where the latter are available. The models agree with each other and with observations on the high Arctic mean cloud amounts in summer. However, large discrepancies are found in the cloud ice and liquid water contents of the models. Recent ground-based observations showed that Arctic clouds have much larger liquid water contents than previously thought. Only CCSM model has large liquid water contents in Arctic clouds, while the clouds in GISS model are characterized by extremely high ice content and very little liquid water content, and HadCM3 model clouds hold small amounts of both. Differences in the model cloud properties cause disagreements in the cloud short wave forcing and thus solar radiation reaching the surface. Summer sea ice concentrations and surface albedo crucial for the surface net absorbed solar radiation also vary among the models. In June, the differences between GISS-Er and CCSM models in the surface short wave incoming flux and net absorbed flux averaged over the ocean north of 70°N are 52 and 27 W/m², respectively. In each model, the different repesentations of the surface and cloud properties compensate, reducing the errors in the radiative balance at the top of the atmosphere. Such compensating effects of the surface and cloud properties on the short wave radiation budget can cause large uncertainties in the prediction of the Arctic climate future changes. More observations are needed to validate the model representation of these essential climate parameters.
DE: 0750 Sea ice (4540)
DE: 3310 Clouds and cloud feedbacks
DE: 3337 Global climate models (1626, 4928)
DE: 3359 Radiative processes
SC: Cryosphere [C]
MN: Fall Meeting 2005