HR: 08:15h
AN: A41B-02 INVITED     [Abstracts]
TI: The Development of the Eta Regional Climate Model and its Application to Warm Season Precipitation Simulation
AU: * Mitchell, K
EM: Kenneth.Mitchell@noaa.gov
AF: NCEP Environmental Modeling Center, NOAA Science Center (Room 207) 5200 Auth Road, Camp Springs, MD 20746-4304
AU: Yang, R
EM: Rongqian.Yang@noaa.gov
AF: NCEP Environmental Modeling Center, NOAA Science Center (Room 207) 5200 Auth Road, Camp Springs, MD 20746-4304
AB: To examine seasonal climate predictability using a regional model, in this study we developed and tested a high resolution, Eta model-based, Regional Climate Model (Eta RCM). The model was based on the NCEP operational Eta model (as of the spring of 2003, namely, the Eta model version in the NCEP 25-year Regional Reanalysis), with changes made to make the model run over a longer time period and to update the sea surface temperature (SST), sea ice, green vegetation fraction, and surface albedo fields on a daily basis. For this study, we executed the Eta RCM on the same large domain as used in both the operational Eta model and the Regional Reanalysis (RR), and using a resolution identical to that of the RR (32 km horizontally and 45 levels vertically). Presently, the model can be executed off of analyzed lateral boundary conditions of the NCEP Global Reanalysis 1 and 2, or predicted lateral boundary conditions from NCEP's global Coupled Forecast System (CFS) used for seasonal climate prediction. To examine the impact of the chosen source of initial land states and to test the skill of the Eta RCM in summer precipitation simulations, two interannual pairs of summer cases were chosen, namely, 1990 versus 1991 and 1988 versus 1993. The years 1990 and 1991 were wet and dry years, respectively, in the southwest U.S. monsoon region of interest to the North American Monsoon Experiment (NAME). The years 1988 and 1993 are known for their central U.S. drought and flood episodes, respectively. Most previous studies of RCM seasonal simulations driven by global reanalysis lateral boundary conditions and observed SST utilize one single member initialized from one single date. In contrast, we executed six members whose starting dates vary by one and a half days. The simulation period is from late May through September. In addition to executing an ensemble of realizations, we tested two different sources for the initial land states (soil moisture and soil temperature), namely, one from the NCEP/DOE Global Reanalysis 2 (GR2) and one from the NCEP Regional Reanalysis (RR). We examine the resulting Eta RCM seasonal simulations of precipitation to a) demonstrate the impact of the source of initial land states, b) illustrate whether the simulations capture reasonable interannual variability, and c) examine the extent of member-to-member variability. The results show that the use of RR rather than GR2 initial land states significantly increases the precipitation amounts in the monsoon region of the southwest U.S. and northwest Mexico. Additionally the 1990 versus 1991 simulations capture a meaningful signature of the observed interannual precipitation difference over the monsoon region. Similarly, the 1988 (drought) versus 1993 (flood) simulations reasonably capture the observed interannual precipitation difference over the central U.S. Lastly, significant spread in the precipitation patterns is evident among the six members, indicating that previous RCM studies that employed only one member may be misleading by failing to represent the inherent internal variability in the simulations of RCMs executed over large domains.
DE: 0315 Biosphere/atmosphere interactions
DE: 0325 Evolution of the atmosphere
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting