Wednesday, 17 January 2007: 8:30 AM
Seasonal Precipitation Predictions over North American using the Eta RegionalClimate Model
214B (Henry B. Gonzalez Convention Center)
To examineclimatepredictability on seasonal timescales using regionalclimate models, in this study we continue our advancement and testing of a high resolution, Eta model based Regional Climate Model. The model is an adaptation of the NCEP operational Eta NWP model as of 24 July, 2001, with changes made to make the configuration of the model execution consistent with the longer time scales of seasonal forecasts, including daily updates to the fields of sea surface temperature, sea ice cover, green vegetation cover, and albedo. To test the skill of the Eta RCM in predicting both cold and warm season anomalies of precipitation, the 1999-2004 summercases were chosen. In contrast to many previous RCM studies driven by analysis lateral boundary conditions and initialized from one single date, we used an ensemble approach in both a simulation mode, using observed SSTs and analyzed boundary conditions from the NCEP Global Reanalysis II, and a seasonal prediction mode, usingthe predicted SSTs and lateral boundary conditions from the latest NCEP Coupled Forecast System (CFS). The Eta RCM was run from ten different initial dates starting from Mid-April for the summer runs, and seven different initial dates for the winter runs. Our focus in this study is the seasonal predictability of both summer and winter season precipitation and to what extent the Eta RCM predictability does or does not show improved skill or value-added attributes via downscaling,relative to the driving CFS global model ensemble predictions.
We examine the resulting ensemble mean and individual members to demonstrate a) whetherthe Eta RCM successfully simulates/predicts total precipitation over the U.S. by using the regional climate modeling approach compared to the original CFS runs, and b) the predictability in terms of the choice of both SSTs and lateral boundary conditions. The results show that the Eta RCM has notable sensitivity to the choice of SSTs and lateral boundary conditions,with substantial member-to-member variability.