ALBERT

Description / Table of Contents: One of the largest uncertainties in determining the effect of CFC’s on stratospheric ozone has been the magnitude of the trends in the altitude region between 15 and 20 km. In the 1994 WMO-UNEP ozone assessment, SAGE was reported as giving trends up to -0± 8% per decade at northern mid-latitudes, while the ozonesonde stations gave a trend of -± 3% per decade. In 1996 the SPARC panel on Understanding Ozone Trends and the International Ozone Commission decided to collaborate, under the auspices of the World Climate Research Programme and the World Meteorological Organisation, on a study to carefully re-evaluate the ground-based and satellite data to resolve this discrepancy. The philosophy of the study was similar to that of the International Ozone Trends Panel of 1988 which addressed the total ozone measurements. The published literature was not simply reviewed, but a critical re-analysis and interpretation of the vertical profiles of ozone was performed. One of the principal aims of the report was to determine if there was sufficient confidence in the long-term measurement systems to use them for accurate determination of ozone trends in the stratosphere and troposphere. A major purpose of the study was to validate the quality of the data including quantification of the errors and to determine if there were any limitations in altitude or latitude. The report is divided into three main chapters. Chapter 1 contains a description of how the various instruments work, and how ozone concentrations are calculated from the raw measurement. Particular attention is paid to the true vertical resolution of each instrument’s measurement and to its long term calibration drift as well as to its precision and accuracy. Chapter 2 assesses how well the various measurements agree through a series of rigorous data comparisons. Traditional techniques based on zonal averages and on close matches in time and space are augmented by new techniques which classify the air mass according to its dynamic history. Chapter 3 discusses and uses the various methods available for calculating trends, as well as investigating how well the causes of the trends can be determined by statistical approaches.

Description / Table of Contents: This scientific assessment has been carried out by the WCRP project on Stratospheric Processes and their Role in Climate (SPARC). The objective of the report is to critically review measurements of water vapour in the stratosphere and upper troposphere, in order to consolidate our knowledge and understanding of the distribution of water vapour and its variability on time scales ranging from the seasonal to the long-term inter-annual. Considering the fundamental role of water vapour in climate, and the scarcity of information concerning its distribution, variability and long-term evolution, the need for such an assessment was recognised by the SPARC Scientific Steering Group. The lack of knowledge on water vapour also leads to a large uncertainty in the prediction of climate change. One of the objectives of the assessment was therefore to support the Third IPCC Assessment Report on Climate Change due to be published in 2001. Great effort has been made to prepare the best data sets possible, to retrieve historical data sets, and to make them all available to the assessment team. This report contains an extensive description of the measurements and their associated uncertainties, an assessment of data quality based on comparison studies of the various data sets, and a description of the understanding of the distribution and variability of water vapour in the stratosphere and upper troposphere which ensues from the data. Finally, recommendations are made to ensure that the difficulties met during this work are overcome in order that the remaining uncertainties in our knowledge and understanding can be resolved. The preceding summary also appears in SPARC Newsletter number 16 (January 2001). The outline of the assessment was determined during an international workshop held at NCAR, Boulder, Colorado, USA, 26-28 August 1998. The drafts of the chapters were prepared in the following year and a number of new data sets were produced. The first draft report was examined by an international panel of reviewers both by mail peer review and at a meeting in Paris, France in January 2000. During the review meeting the responses to the mail review comments were proposed by the authors and discussed by the participants. This rigorous review greatly improved the report, the contribution of the reviewers being significant. A second draft report was reviewed by mail review in August 2000. The success in producing the Report is the result of the intensive work and enthusiastic cooperation of a large number of scientists world-wide who have worked towards improving the quality of the measurements and our understanding of the observations. The work of the contributors and reviewers was generously supported by many organisations and agencies including WMO, WCRP, SPARC, DG Research of the European Commission, NASA, NOAA, NCAR, CNRS, CNES, Forschungszentrum Jülich, Imperial College and other national research programmes and institutions. We take this opportunity to express our gratitude to all the scientists (authors, contributors and reviewers) who helped in the preparation of this assessment and to the SPARC scientific steering group who have been supportive since its inception. Our special gratitude is due to the lead authors of the chapters. Particular thanks must be given to: Petra Udelhofen at the SPARC Data Center for setting up the data archive, Sam Oltmans who organised the workshop at NCAR, Boulder, Colorado; Computational Physics Inc., for hosting the workshop in Washington D.C.; François Dulac from the CNES for hosting the review meeting in Paris, and Céline Phillips for her co-editorship. We also thank Marie-Christine Gaucher at the SPARC office for her help in the organisation of the review meeting in Paris and in the final editing of the report and Catherine Michaut at the SPARC office for her help in editing the second peerreview draft and the final draft of the report.

Description / Table of Contents: Assessments of stratospheric ozone have been conducted for nearly two decades and have evolved from describing ozone morphology to estimating ozone trends, and then to attribution of those trends. Stratospheric aerosol has only been integrated in assessments in the context of their effects on ozone chemistry and has not been critically evaluated itself. As a result, the Assessment of Stratospheric Aerosol Properties (ASAP) has been carried out by the WCRP project on Stratospheric Process and their Role in Climate (SPARC). The objective of this report is to present a systematic analysis of the state of knowledge of stratospheric aerosols including their precursors. It includes an examination of precursor concentrations and trends, measurements of stratospheric aerosol properties, trends in those properties, and modeling of aerosol formation, transport, and distribution in both background and volcanic conditions. The scope of this report is extensive; however, some aspects of stratospheric aerosol science have been deliberately excluded. For instance, we have not attempted to include an examination of polar stratospheric clouds (PSCs) or other clouds (such as cirrus clouds) occurring at or above the tropopause except in as much as they influence aerosol observations. Polar stratospheric clouds are the subject of a separate SPARC activity. We have produced a gap-free aerosol data base for use beyond this report. This required some new analysis that has not previously appeared in the technical literature. Similarly, the trend analysis required the development of a new analysis technique that is the subject of an article published in the Journal of Geophysical Research. New work is clearly identified in the present report. ASAP began with a general kick-off meeting in November 2001 at CNES in Paris, France. There were also three chapter lead meetings in Nice, France (April 2003), in Frankfurt, Germany (July 2003) and in Lexington, Massachusetts, USA (January 2004). The final report is the result of concerted effort by scientists world-wide who continue to work toward understanding the measurements and processes controlling stratospheric aerosol. Their work was supported by their host institutions and funding agencies that include the WCRP and the SPARC Office (in Paris and Toronto), as well as Atmospheric and Environmental Research, Inc., NASA, the Universities of Frankfurt and Wyoming, and ETH Zurich. An initial overview of ASAP appeared in the SPARC Newsletter No. 23 in July 2004.

Description / Table of Contents: SPARC has from its outset been concerned with “Stratospheric Indicators of Climate Change,” “Stratospheric Processes,” and “Troposphere/Stratosphere Modelling.” The SPARC project GRIPS (GCM Reality Intercomparison Project) has focused on comparing troposphere/stratosphere general circulation models with one another, both in terms of their technical formulations and in their results. Of course, another aspect of GRIPS is to examine how well model results compare to observations. Direct model/data comparisons are not so straightforward, however. For instance, the stratosphere displays a great deal of interannual variability, so that model-data comparisons necessarily include statistics of both means and variances over comparable time periods. Additionally, stratospheric data are obtained from complicated inversions of radiances derived from satellite measurements, from direct but sparse balloon or rocket measurements, from time continuous but geographically sparse ground-based remote sensing instruments, and finally from analysis of stratospheric measurements either by statistical techniques or from data assimilation methods. The climatologies derived by these different methods do not agree in all respects. Finally, the entire concept of stratospheric trends means that stratospheric climatology is itself time varying. The SPARC Reference Climatology Group was established to update and evaluate existing middle atmosphere climatologies for use in GRIPS, and in other SPARC activities. Rather than create a single new “super climatology,” it was decided that a valuable contribution would be to (1) compile existing climatologies and make them easily available to the research community, and (2) carefully compare and evaluate the existing climatologies. The SPARC Data Center was established (in part) as a response to item (1), and this Report is a response to item (2). Here we present detailed intercomparisons of climatological wind and temperature data sets that are currently used in the research community, which are derived from a variety of meteorological analyses and satellite data sets. Special attention is focused on tropical winds and temperatures, where large differences exist among separate analyses. We also include comparisons between the global climatologies and historical rocketsonde temperature and wind measurements, and also with more recent lidar temperature data. These comparisons highlight differences and uncertainties in contemporary middle atmosphere data sets, and allow biases in particular analyses to be isolated. In addition, a brief atlas of zonal mean wind and temperature statistics is provided to highlight data availability and as a quick-look reference. This Report is intended as a companion to the climatological data sets held in archive at the SPARC Data Center (http://www.sparc.sunysb.edu).

Description / Table of Contents: Three-dimensional climate models with a fully interactive representation of stratospheric ozone chemistry — otherwise known as stratosphere-resolving chemistry-climate models (CCMs) — are key tools for the attribution and prediction of stratospheric ozone changes arising from the combined effects of changes in the amounts of greenhouse gases (GHG) and ozone-depleting substances (ODS). These models can also be used to infer potential effects of stratospheric changes on the climate of the troposphere. In order to know how much confi dence can be placed in the results from the CCMs, both individually and collectively, it is necessary to assess their performance by comparison with observations and known physical constraints. The Stratospheric Processes And their Role in Climate (SPARC) core project of the World Climate Research Programme (WCRP) initiated the CCM Validation (CCMVal) activity in 2003 to coordinate exactly such an evaluation. The CCMVal concept (see Chapter 1) takes as a starting point the premise that model performance is most accurately assessed by examining the representation of key processes, rather than just the model’s ability to reproduce long-term ozone trends, as the latter can be more easily tuned and can include compensating errors. Thus a premium is placed on high-quality observations that can be used to assess the representation of key processes in the models. This Report does not provide a detailed assessment of the quality of the observational databases; the compilation and assessment of data sets suitable for model evaluation is the focus of a future SPARC activity, which has been motivated by this Report. The fi rst round of CCMVal (CCMVal-1) evaluated only a limited set of key processes in the CCMs, focusing mainly on dynamics and transport. This Report, which describes the second round of CCMVal (CCMVal-2), represents a more complete effort by CCMVal to assess CCM performance. As with CCMVal-1, it also includes an assessment of the extent to which CCMs are able to reproduce past observations in the stratosphere, and the future evolution of stratospheric ozone and climate under one particular scenario. A key aspect of the model evaluation within this Report is the application of observationally-based performance metrics to quantify the ability of models to reproduce key processes for stratospheric ozone and its impact on climate. The Report is targeted at a variety of users, including: (1) international climate science assessments, including the WMO/ UNEP Ozone Assessments and the IPCC Assessment Reports; (2) the CCM groups themselves; (3) users of CCM simulations; (4) measurement and process scientists who wish to help improve CCM evaluation; (5) space agencies and other bodies involved in the Global Climate Observing System. The Report was prepared by dozens of scientists and underwent several revisions and extensive peer review, culminating in a Final Review Meeting in Toledo, Spain on November 9-11, 2009.