HR: 10:50h
AN: A32A-03    [Abstracts]
TI: Spectral Nudging to Eliminate the Effects of Domain Position and Geometry in Regional Climate Model Simulations
AU: * Miguez-Macho, G
EM: gonzalo@envsci.rutgers.edu
AF: Department of Environmental Sciences, Rutgers University, 14 College Farm Rd. , New Brunswick, NJ 08901 United States
AU: stenchikov, G L
EM: gera@envsci.rutgers.edu
AF: Department of Environmental Sciences, Rutgers University, 14 College Farm Rd. , New Brunswick, NJ 08901 United States
AU: Robock, A
EM: robock@envsci.rutgers.edu
AF: Department of Environmental Sciences, Rutgers University, 14 College Farm Rd. , New Brunswick, NJ 08901 United States
AB: Previous regional climate simulations have exhibited great sensitivity to the size and position of the domain chosen for calculations. Using the Regional Atmospheric Modeling System (RAMS) we performed several experiments using a 7500 km x 5400 km grid over North America and 50 km resolution to investigate the physical and numerical mechanisms involved. The simulation period was June of 2000 and all experiments have NCAR/NCEP reanalysis as initial and boundary conditions and the same exact model settings. For each simulation we displaced the center of the grid in a different direction, always keeping the U.S. in the interior, out of the buffer zone. Circulation biases presented a large scale structure, organized by the Rocky Mountains, resulting from a systematic shifting of the synoptic wave trains that crossed the domain. The distortion of the large-scale circulation was produced by interaction of the modeled flow with the lateral boundaries of the nested domain and varied when the position of the grid was altered. This changed the large-scale environment among the different simulations and translated into diverse conditions for the development of the mesoscale processes that produce most of precipitation for the Great Plains in the summer season. As a consequence, precipitation results varied, sometimes greatly, among the experiments with the different grid positions. We performed additional experiments to assess the effect of the position of the domain on commonly studied sensitivities, such as those to soil moisture, and the response also showed variations among the simulations with different grid positions. To eliminate the dependence of results on the position of the domain we used a spectral nudging technique, where waves longer than 2,500 km above the boundary layer were relaxed to those from reanalysis. Moisture was not nudged at any level. This constrained the synoptic circulation to follow reanalysis while allowing the model to develop the small-scale dynamics responsible for the rainfall. We repeated the experiments with the different grid positions with spectral nudging and the sensitivity of precipitation to the position of the domain was virtually eliminated.
DE: 3329 Mesoscale meteorology
DE: 3337 Numerical modeling and data assimilation
DE: 3354 Precipitation (1854)
DE: 3319 General circulation
DE: 1620 Climate dynamics (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting