A Multiseason Climate Forecast System at the National Meteorological Center

Abstract

The Coupled Model Project was established at the National Meteorological Center(NMC)in January l991 to develop a multiseason forecast system 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 expertise in atmospheric modeling and data assimilation in the Development Division. Since the inception of the project, considerable progress has been made toward establishing a coupled forecast system. A T40 version of NMC's operational global medium-range forecast model (MRF) has been modified so as to have improved response to boundary forcing from the Tropics. In extended simulations, which are forced with observed historical global sea surface temperature (SST) fields, the model reproduces much of the observed tropical Pacific and North American rainfall and temperature variability. An ocean reanalysis has been performed for the Pacific basin starting from July 1982 to present and uses a dynamical model-based as assimilation system. This also provides the ocean initial conditions for coupled fore cast experiments. The current coupled forecast model consists of an active Pacific Ocean model coupled to the T4Oversion of the NMC's MRF. In the future, a global ocean model will be used to include climato information from other ocean basins. 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 experiments. Work is currently under way to quantity the skill in predicting climatic variability over North America.