HR: 1340h
AN: A53A-0850    [Abstracts]
TI: Downscaling Ability Of NCEP Regional Spectral Model, Version 97: The Big Brother Experiment
AU: * Herceg, D
EM: dh2006@columbia.edu
AF: Department of Applied Physics and Applied Mathematics, Columbia University 292B S.W. Mudd Bldg. 500 W 120th Street, New York City, NY 10027
AU: Sobel, A
EM: ahs129@columbia.edu
AF: Department of Applied Physics and Applied Mathematics, Columbia University 217 S.W. Mudd Bldg. 500 W 120th Street, New York City, NY 10027
AU: Sun, L
EM: sun@iri.columbia.edu
AF: International Research Institute For Climate Prediction (IRI), Lamont-Doherty Earth Observatory 231 Monell Bldg. P.O. Box 1000, Palisades, NY 10964
AU: Zebiak, S
EM: steve@iri.columbia.edu
AF: International Research Institute For Climate Prediction (IRI), Lamont-Doherty Earth Observatory 226 Monell Bldg. P.O. Box 1000, Palisades, NY 10964
AB: Regional climate modeling has become an important tool for the prediction of climatic changes in the past few decades. Current General Circulation Models (GCMs) still have resolutions too low to be able to resolve small-scale atmospheric circulation features, such as may be produced by orography or regional land surface details. Instead, limited-area models have been used to produce climatic simulations of certain regions with boundary conditions derived from observational data or a global General Circulation Models. The Big Brother Experiment (BBE) consists of first providing the reference climate by performing the large domain high resolution regional climate model simulation (The Big Brother). Then, this reference simulation is degraded by filtering out short scales that still remain unresolved in the GCMs. This new, filtered reference climate is then used to drive the same regional climate model (RCM) integrated at the same resolution as the Big Brother, but over a smaller domain embedded in the larger domain. This smaller domain simulation is called the Little Brother. We then finally compare the climate statistics of the Little Brother with those of the Big Brother over the Little Brother Domain. Since the same model is used for both the Big Brother and Little Brother experiments, any difference in the solutions can only be attributed to the nesting strategy. A good comparison between the two solutions is a necessary, though not sufficient prerequisite for the use of the standard one-way nesting strategy for regional climate modeling. Our study extends that of Denis et al. (2001) by using a different model, and mainly focusing on tropical rather than extratropical experiment. Our primary domains are located in the tropics of the South America and the Atlantic Ocean, with spatial resolution of 60 km, 180 x 181 grid points for Big Brother, 90 x 91 grid points for the Little Brother, and vertically, 19 model levels (18 layers). The simulation was completed for April 1994. The Big Brother simulation was driven directly by the ECHAM4.5 global model data set, archived every 6 hours. The Big Brother output was saved every 6 hours as well, for the nesting of the Little Brother. The initial experiments yielded that the small-scale features that were absent from the initial conditions were almost fully recovered within the first 24 hrs in most variables, except for the precipitation. The time variability of the daily domain-averaged precipitation patterns was well reproduced. The results obtained in our primary experiment resulted in further experimentation over a midlatitudes of North American continent. These simulations have yielded a significant improvement in recovery of the small-scale features, especially in the precipitation field, which will be presented in more detail. The paper is expected to be in press this Fall.
DE: 9325 Atlantic Ocean
DE: 9360 South America
DE: 3337 Numerical modeling and data assimilation
DE: 3374 Tropical meteorology
DE: 3210 Modeling
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting