HR: 0800h
AN: A31A-0020    [Abstracts]
TI: Coupled versus Uncoupled Atmospheric Model Integrations
AU: * Shin, S
EM: Sangik.Shin@noaa.gov
AF: Climate Diagnostics Center/CIRES/University of Colorado and Physical Sciences Division/ESRL/NOAA, R/PSD1, 325 Broadway, Boulder, CO 80305,
AU: Sardeshmukh, P D
EM: Prashant.D.Sardeshmukh@noaa.gov
AF: Climate Diagnostics Center/CIRES/University of Colorado and Physical Sciences Division/ESRL/NOAA, R/PSD1, 325 Broadway, Boulder, CO 80305,
AB: The utility of atmospheric general circulation model (GCM) integrations with prescribed sea surface temperatures (SSTs) is increasingly being questioned in the contexts of climate diagnosis, climate model error diagnosis, and short-term climate predictions. The basic issue is to what extent the errors in surface heat fluxes caused by decoupling air-sea interactions in this manner affect climate variability and the mean climate. This issue is addressed here by generating and comparing multi-century coupled GCM simulations with corresponding atmospheric GCM simulations with prescribed SSTs obtained from the coupled simulations. When the SST time series is prescribed at the full (half-hourly) temporal resolution of the coupled model output, the uncoupled simulations have a negligibly small mean climate bias, small variance errors on subseasonal scales, and slightly larger variance errors on interannual and decadal scales. Even on decadal scales, however, the errors are notably smaller than anticipated from altered local thermal damping considerations alone. When the SSTs are prescribed at monthly temporal resolution, the mean bias remains small but the variance errors become larger, especially on subseasonal scales. When only the long-term mean SST seasonal cycle is prescribed, the variance errors become large, not surprisingly, also on the interannual and decadal scales. There is now also an appreciable mean bias, arising mainly from the atmospheric GCM's response to El Nino SST anomalies being larger than that to La Nina SST anomalies. Overall, these results show that the errors introduced by prescribing SSTs in atmospheric GCMs, though not negligible, are generally much smaller than the atmospheric response to the SSTs themselves. To that extent, they justify performing and using such uncoupled integrations for diagnostic and prediction purposes.
DE: 1620 Climate dynamics (0429, 3309)
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3319 General circulation (1223)
DE: 3334 Middle atmosphere dynamics (0341, 0342)
DE: 3362 Stratosphere/troposphere interactions
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting