The New Seasonal Forecast Model at NCEP

A new global coupled atmosphere-ocean forecast model (CFS03) has recently been developed at the U.S. National Centers for Environmental Prediction (NCEP). CFS03 consists of a T62L64 version of the operational NCEP Atmospheric Global Forecast System (GFS03) and the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model version 3 (MOM3). CFS03 is expected to replace the current NCEP operational coupled seasonal forecast model this year. The coupled model has been integrated for over 30 years without flux corrections in an effort to examine the model climatology. Increasing the number of vertical levels in the atmospheric model from 28 to 64 levels resulted in substantially better simulation of equatorial sea surface temperatures (SST). The model is capable of simulating the earth’s climate with a very small bias in the equatorial SST of less than 1 K. The CFS03 realistically simulates ENSO variability with amplitude and frequency comparable to that observed. The model reproduces the observed ENSO seasonal phase locking with the peak phase near the end of the year, although the initial warming from January to May of the simulated El Nino events is somewhat too strong.

We are currently generating a 23-year database of hind-casts to provide the model climatology for real-time prediction bias corrections and to provide estimates of real-time forecast reliability. Results from the hind-casts indicate more skill in forecasting SSTs in the equatorial Pacific than the current operational seasonal forecast system. Results from the hind-casts and from CMIP integrations will be presented. Plans for further development of the seasonal forecast system will be discussed.