ATMOSPHERIC OBSERVATIONS AND EXPERIMENTS TO ASSESS THEIR USEFULNESS IN DATA ASSIMILATION

Atmospheric observations consist of a mixture of in situ, visual, and remotely sensed observations. These provide an extensive database for research and numerical weather prediction. However, significant data d eficiencies still exist, and new observing systems are continually bei ng proposed. Observing system experiments (OSE's) are conducted to ass ess the usefulness of different types of existing atmospheric observat ions. Observing system simulation experiments (OSSE's) are conducted t o evaluate the potential impact of proposed observing systems, as well as to determine tradeoffs in their design, and to evaluate data assim ilation methodology. This paper contains a review of the development o f the global atmospheric observing system, a description of the princi pal types of data, an overview of OSE and OSSE methodology, and result s from recent experiments to evaluate the relative utility of the prin cipal atmospheric observing systems and the potential for new observin g systems. These experiments show the critical contributions being mad e by both conventional and space-based observations, and indicate cons iderable potential for future satellite observing systems to improve d ata assimilation.