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To investigate the effects of the middle atmosphere on climate, the World Climate Research Programme is supporting the project "Stratospheric Processes and their Role in Climate" (SPARC). A central theme of SPARC, to examine model simulations of the coupled troposphere-middle atmosphere system, is being performed through the initiative called GRIPS (GCM-Reality Intercomparison Project for SPARC). In this paper, an overview of the objectives of GRIPS is given. Initial activities include an assessment of the performance of middle atmosphere climate models, and preliminary results from this evaluation are presented here. It is shown that although all 13 models evaluated represent most major features of the mean atmospheric state, there are deficiencies in the magnitude and location of the features, which cannot easily be traced to the formulation (resolution or the parameterizations included) of the models. Most models show a cold bias in all locations, apart from the tropical tropopause region where they can be either too warm or too cold. The strengths and locations of the major jets are often misrepresented in the models. Looking at three-dimensional fields reveals, for some models, more severe deficiencies in the magnitude and positioning of the dominant structures (such as the Aleutian high in the stratosphere), although undersampling might explain some of these differences from observations. All the models have shortcomings in their simulations of the present-day climate, which might limit the accuracy of predictions of the climate response to ozone change and other anomalous forcing.

[1] The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics satellite has delivered over 1 year of radiance profile data from which middle atmosphere temperature profiles have been retrieved. Version 1.01 temperatures are precise and sufficiently accurate, such that one can obtain estimates of their synoptic distributions on pressure surfaces. A sequential estimation algorithm was used to generate daily, zonal Fourier coefficients of temperature (through zonal wave number 6), and maps on constant pressure surfaces were generated using those coefficients. Maps of temperature, geopotential height, and geostrophic winds are compared with products from the Met Office analyses. Stratospheric differences are within about 2 K for temperature and 160 m for geopotential height. The respective wind fields indicate flow patterns that are similar. Examples of the fields are shown for a period in February 2002 during a sudden stratospheric warming event that occurred in the Northern Hemisphere. A cooling of the middle mesosphere accompanies the warming. It is anticipated that large-scale, middle atmospheric dynamics and transport studies can be undertaken and that data assimilation products can be extended to near the mesopause using the SABER profiles.

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