A MULTISEASON CLIMATE FORECAST SYSTEM AT THE NATIONAL-METEOROLOGICAL-CENTER

The Coupled Model Project was established at the National Meteorologic al Center (NMC) in January 1991 to develop a multiseason forecast syst em based on coupled ocean-atmosphere general circulation models. This provided a focus to combine expertise in near real-time ocean modeling and analyses situated in the Climate Analysis Center (CAC) with exper tise in atmospheric modeling and data assimilation in the Development Division. Since the inception of the project, considerable progress ha s been made toward establishing a coupled forecast system. A T40 versi on of NMC's operational global medium-range forecast model (MRF) has b een modified so as to have improved response to boundary forcing from the Tropics. In extended simulations, which are forced with observed h istorical global sea surface temperature (SST) fields, the model repro duces much of the observed tropical Pacific and North American rainfal l and temperature variability. An ocean reanalysis has been performed for the Pacific basin starting from July 1982 to present and uses a dy namical model-based assimilation system. This also provides the ocean initial conditions for coupled forecast experiments. The current coupl ed forecast model consists of an active Pacific Ocean model coupled to the T40 version of the NMC's MRF. In the future, a global ocean model will be used to include climate information from the other ocean basi ns. The initial experiments focused on forecasting Northern Hemisphere winter SST anomalies in the tropical Pacific with a lead time of two seasons. The coupled model showed considerable skill during these expe riments. Work is currently under way to quantify the skill in predicti ng climatic variability over North America.