The Canadian Global Data Assimilation System: Description and Evaluation

A global data assimilation system has been in operation at the Canadian Meteorological centre (CMC) since March 1991 when it replaced the previous hemispheric system. This paper describes the system and presents an evaluation of its performance from several points of view, including the fit of the analyses and short-range forecasts to observations, the relative roles of various components of the system, the functioning of some specific subcomponents in a particular case, and the ability of the system to represent important aspects of the mean monthly general circulation. This latter part of the evaluation includes comparisons with the corresponding statistics derived from the analyses of the National Meteorological Center.The global data assimilation system is found to be functioning well, especially in extratropical regions with reasonable data coverage. Problems and weaknesses of the system are discussed.