1. The Eta Regional Climate Model: Model Development and Its Sensitivity in NAMAP Experiments to Gulf of California Sea Surface Temperature Treatment Rongqian Yang and Kenneth Mitchell Environmental Modeling Center National Centers for Environmental Prediction

2. The Eta Regional Climate Model Development at NCEP Developed: uses very recent version of Eta Model physics As implemented in operational NCEP Eta on 24 Jul 01 Virtually exact match to Eta model in Regional Reanalysis (R/R) R/R domain and grid (32-km, 45-levels, large R/R domain) R/R Eta model physics, e.g. NOAH Version 2.3 with R/R 4 soil layers NCEP will provide as a community workstation Eta RCM

3. Executions: summer seasonal simulations (32-km) Summers 1990 (NAME choice, with and without Baja) and 1991 Temporal lateral boundary conditions: Used NCEP/NCAR Global Reanalysis II (6-hourly) Daily updates of several surface boundary fields: Daily observed 1-deg weekly Reynolds/Stokes SST (NCEP) Satellite NDVI-based 0.15-degree monthly greenness (NESDIS) Seasonal 1.0-deg snow-free albedo climatology (NASA) Initial land states of soil moisture and soil temperature Soil moist/temp from Global Reanalysis II --- plan to repeat with Regional Reanalysis land states Snow depth: USAF operational 47-km daily global snow depth Model Simulations

5. GoC SST Treatment 1x1 degree Reynolds/NCEP SST treatment does not capture observed summer warming of GOC Correction method developed by David Stensrud for use with the Penn State/NCAR mesoscale model, modified for Eta model by Tom Black 1. Alter SSTs in the Gulf of California to a areal mean value, valid near Guaymas, Mexico 2. This treatment defines mean GoC SST values valid at the beginning of each month. Then performs temporal interpolation to get SST at any date

6. GoC Land Sea Mask and SST Treatment

19. Discussions The GoC is only a small area relative to the model domain. Both treatments in the GoC SST can make a difference in the local circulation and precipitation patterns in the GoC region, demonstrating that the model can capture the difference arising from using both treatments although the model has great inherent internal variability The results suggest that SST (resolution and quality) play an important role in regional climate modeling. Need to test the impact of domain size on model results

20. Conclusions The GoC SST treatment has important impact to local low- level circulations and precipitation pattern in the GoC region The GoC SST treatment has relatively small impact on large scale and upper level circulations The results suggest that the GoC SST must be taken into account in order to model North American Monsoon correctly