HR: 08:00h
AN: A41B-01 INVITED     [Abstracts]
TI: Internal Variability in Nested Regional Climate Simulations
AU: * Arritt, R W
EM: rwarritt@bruce.agron.iastate.edu
AF: Iowa State University, 3010 Agronomy Hall, Ames, IA 50011 United States
AB: The high computational cost of regional climate simulations has meant that studies using regional climate models usually have relied on single realizations for each situation of interest. In some cases the sensitivity to different physical parameterizations, domain sizes, or other aspects of model configuration have been examined, but again there has almost always been only a single realization for each configuration. This raises the question of whether conclusions can reliably be drawn from a single realization; i.e., we must ask, What is the magnitude of internal variability in a regional climate model? Here we evaluate three realizations using the regional climate model RegCM3 to simulate the period 1986-2003 over a domain covering the continental U.S. and most of Mexico at 52 km grid spacing. Initial and lateral boundary conditions were taken from the NCEP-DOE Reanalysis 2. The three RegCM3 realizations were initialized one month apart but were otherwise identical in configuration, so that their collective behavior provides a measure of internal variability of the model. Internal variability is found to differ both by subregion and by season. Precipitation fields produced by the ensemble members tend to diverge during the warm season and then re-converge during the cool season. Spread of the ensemble precipitation is smallest for regimes that have a summer-dry (Mediterranean) climate. Reasons for internal variability are discussed, most notably the roles of soil moisture, convective precipitation, and feedbacks between moisture and precipitation.
DE: 3337 Numerical modeling and data assimilation
DE: 3354 Precipitation (1854)
DE: 1866 Soil moisture
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting