Understanding Stratospheric Processes and their Role in Climate The Ninth Annual Meeting of the SPARC Scientific Steering Group

T he IPRC played host to the 9th annual meeting of the Scientific Steering Group (SSG) of the SPARC (Stratospheric Processes and their Role in Climate) program last December. SPARC is one of the six main initiatives of the World Climate Research Programme and focuses on understanding and modeling the circulation and chemistry of the stratosphere, and how these influence and are influenced by tropospheric climate and climate change. The meeting participants discussed a range of current issues relating to stratospheric circulation and climate. In the 1990s, SPARC undertook major assessments of trends observed in stratospheric temperature, ozone, and water vapor over the last few decades. The SSG considered how to update these assessments and formulated plans for assessing the observed trends in stratospheric aerosol concentration. Preliminary plans were discussed for a more integrative assessment of the consistency of the observed temperature trends and the coincident changes in atmospheric composition. In addition to these assessment efforts, the SSG reviewed some other activities SPARC has undertaken in order to advance understanding of certain key physical processes. A notable example among these is the effort to apply routinely collected, operational upper-air weather data to the study of the gravity-wave field in the upper tro-posphere and lower stratosphere. Modern radiosonde systems actually record data at quite fine vertical resolution (~100 m, or better). Unfortunately, the standard practice has been to archive only the data at the levels mandated by the World Meteorological Organization (WMO). By saving only the WMO-mandated data, the national meteorological services are discarding potentially important information about the atmosphere. For some years now, Kevin Hamilton (IPRC) with his colleague Robert Vincent (Adelaide University) have led a SPARC-sponsored working group to " rescue, " archive, and analyze the very fine vertical resolution wind and temperature data from operational balloon-borne radiosondes. They have coordinated the accumulation and analysis of the raw data, and through their effort, suitable data have been obtained from over 190 stations provided by the national meteorological services of 12 countries. The SSG reviewed these achievements along with preliminary scientific analyses that have examined the geographical and seasonal variability in the wave-like fluctuations seen in these data. The activities of other SPARC working groups were reviewed, including one devoted to understanding the dynamical and chemical structure of the tropopause region, and another that is conducting a series of intercomparisons of results from several global simulation models with substantial resolution …