S P A R C Stratospheric Processes And their Role in Climate A project of the World Climate Research Programme Home Initiatives Organisation Publications Meetings Acronyms and Abbreviations Useful Links

1. Introduction

The goal of the WCRP's (World Climate Research Programme) SPARC (Stratospheric Processes and Their Role in Climate) project is to understand and model stratospheric impacts on climate. To accomplish this goal, SPARC is taking a three-pronged approach. SPARC efforts are underway to document and interpret indicators of stratospheric change such as trends in temperature, ozone, water vapour, and dynamics. There are also SPARC efforts to improve our understanding of stratospheric processes that are needed for proper modelling of the climate system. These processes include stratospheric dynamics and transport, upper troposphere-lower stratosphere chemistry and microphysics, and gravity wave processes. Finally, there are SPARC efforts to improve climate prediction by properly including the stratosphere. To accomplish this, there is a SPARC group focused on understanding and improving general circulation models that include the troposphere and stratosphere. There is another group that is compiling climatology statistics for the stratosphere for comparison with models as well as documenting the behaviour of the troposphere-stratosphere system. Part of this climatology is documenting the modes of stratospheric variability, both natural and that arising from anthropogenic influences. The stratospheric quasi-biennial oscillation (QBO) is a dominant mode of interannual variation of the equatorial lower stratosphere, but it also has global influences. One topic that is receiving attention in SPARC is to understand the role of the QBO in coupling the tropical and extra-tropical stratosphere as well as the stratosphere and troposphere. Another SPARC effort is to assemble the stratospheric aspects of climate forcing. A number of modelling studies have been published using different assumptions about the height distribution of ozone changes, for example. This activity will assemble the best estimates of past changes in such parameters as ozone and aerosol concentrations to facilitate better understanding of the modelling uncertainties by making available common inputs for these studies.

To successfully implement this SPARC programme requires activities in several areas. We must fully exploit existing data. We must develop better theories and models for stratosphere/climate interactions. This activity must include ways of assessing which models are closer to reality. There must be laboratory measurement programs to obtain proper parameter values for use in stratosphere/climate models. Finally, there must be measurement programs to obtain needed data for understanding and characterising the atmosphere. Such measurements include both satellite and field observational programs. It is mainly this latter category that SPARC will seek to organise, given the high level of activity of national and international satellite agencies.

SPARC does not operate in a vacuum. Substantial national and international research efforts exist relating to the stratosphere and SPARC does not wish to duplicate existing programs where they are adequate, nor to undertake the international organisation of existing programs, where these programs are already interacting well. Rather, SPARC focuses on areas which are important for stratosphere/climate science but which, for some reason, are not receiving adequate attention.

This document is SPARC's first Implementation Plan. It seeks to explain the rationale for its programs, to present our progress to-date, and to indicate what resources are needed to carry out SPARC's activities. It is organised around its three themes :

• to document and understand indicators of stratospheric change;
• to understand the stratospheric processes needed for proper modelling of the climate system; and
• to improve climate modelling by properly including the stratosphere.

The writing of this Implementation Plan, as well as the research described, would not have been possible without the support of the different national and international funding agencies and research bodies, thanks to whom SPARC-related research is carried out, and who permitted the scientists involved in SPARC to dedicate so much of their time to the programme.