CHARACTERISTICS OF STRATOSPHERIC WINDS AND TEMPERATURES PRODUCED BY DATA ASSIMILATION

Data assimilation is a vital technique in modem meteorology, allowing information from a wide range of observations to be combined to produc e synoptic analyses of the atmospheric circulation. Data assimilation has a number of advantages over conventional analysis methods that ste m from the use of a numerical model of the atmosphere as an integral p art of the technique. The model provides a framework which allows info rmation from observations to be combined with our understanding of the atmosphere, as embodied in the model, so that a consistent, evolving, three-dimensional picture of the atmospheric circulation may be const ructed. The aim of this paper is to compare results from two different stratospheric data assimilation systems (from Goddard Space Flight Ce nter and the U.K. Meteorological Office) to assess the reliability of analyses derived by using assimilation techniques. In particular, this paper concentrates on assessing the quality of the analyses for long- term transport studies. First, the zonal mean circulations are compare d, with emphasis on the consistency of the residual circulation. Secon d, horizontal transport processes are compared, with particular emphas is on the representation of features in the neighborhood of the winter time polar vortex. It is shown that the two analyses give a broadly co nsistent picture of the atmospheric circulation. Where differences are identified, they can often be attributed to particular shortcomings i n one of the assimilation systems. The results presented here stress t he usefulness of data assimilation for stratospheric studies.