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The 26th Session of the Joint Steering Committee of the WCRP

A. O'Neill, University of Reading, UK (alan@met.rdg.ac.uk)
N. McFarlane, SPARC IPO, University of Toronto, Canada (Norm.McFarlane@ec.gc.ca)

The 26th session of the Joint Steering Committee (JSC) was held at the Escuela Superior Politecnica del Litoral (ESPOL) in Guayaquil, Ecuador. A.
O’Neill and N. McFarlane attended on behalf of SPARC. Although an important aspect of the JSC sessions involves reviewing progress toward achieving WCRP objectives, particularly within the core projects (CliC, CLIVAR, GEWEX, and SPARC), these sessions also provide an ideal opportunity to examine new approaches and ideas.An important part of this year’s meeting involved consideration of the report of the Task Force that was set up at the 25th session to further development of the WCRP strategic framework entitled Coordinated Observation and Prediction of the Earth System (COPES). A Modelling Panel and a Working Group on Observation and Assimilation of the Climate System were also set up to support the COPES and facilitate coordination of modelling and observational activities across the WCRP.

A number of special topics were also placed on the agenda for discussion at the JSC session this year. The topic of Atmospheric Chemistry and Climate was among these. SPARC, in collaboration with IGAC, has developed a high level of expertise and experience in this area and consequently was asked to lead the discussion. To facilitate discussion, a short report entitled “Chemistry-Climate Interactions” was submitted by the SPARC Co-Chairs for consideration of the JSC prior to the session. In his presentation on this topic A. O’Neill emphasized the importance and breadth of atmospheric chemistry and climate interactions as a WCRP issue, noting among other things that (a) the link between air pollution and climate is a key issue for society, (b) chemical processes affecting atmospheric composition are, in general, coupled and nonlinear. He then posed the following questions for consideration by the JSC in regard to Atmospheric Chemistry and Climate (AC&C):

• What are the concrete objectives: chemical weather and climate prediction and scientific underpinning within the seamless prediction of COPES?
• Besides SPARC, what will other WCRP Projects do?
• Should SPARC continue to take the lead? What about tropospheric chemical modelling?
• How is the link with IGAC working? IGBP view?
• Is progress fast enough?
• What should happen now?

The JSC thanked A. O’Neill for his presentation on AC&C. In reply, it reaffirmed the importance of AC&C issues to WCRP’s objectives and stressed the need for developing a roadmap for chemistry-climate models, observations and process studies. For this purpose, the JSC proposed the establishment of a Joint WCRP-IGBP Task Force (TF) involving WCRP core projects and working groups and IGBP (IGAC), led by SPARC and IGAC as the core-organizers. IPCC and possibly IHDP should be kept informed. The immediate task for the TF is to organize a workshop; outcomes of this workshop should be the terms of reference and suggestions for the way forward.

In his presentation to the JSC on SPARC, A. O’Neill summarized developments within the last year, noting that the Third SPARC General Assembly was very successful and that there was a smooth transition of the SPARC Office from Paris to Toronto. The main part of the presentation was devoted to highlighting a number of scientific and technical issues of concern to SPARC and putting before the JSC a number of questions pertaining to them. The first two of these questions relate to the SPARC theme of chemistry- climate interactions and to the earlier presentation and discussion on atmospheric chemistry and climate. They are also motivated in part by the current uncertainty in predictions of the Antarctic ozone minimum by chemistry-climate models (e.g. as reported in the paper by Austin et al., 2003):

• What is SPARC’s role in the chemistry climate initiative?
• Should SPARC’s Chemistry-Climate Modelling Validation project lead to another AMIP-like experiment, and how should it be facilitated?

The JSC affirmed that SPARC should play a leading role in the Joint WCRP-IGBP Task Force. It encouraged SPARC to open discussions with PCMDI to determine if it could help in facilitating an AMIP like experiment for GCMs with well resolved stratospheres and relatively comprehensive treatments of chemistry.

Validation of models places heavy reliance on global observational data sets and/or analyses. Changes in observing systems may give rise to spurious apparent changes in physical variables such as temperature, prompting the following question:

• What needs to be done at a “high level” to ensure that the temperature record derived from satellites is cross-calibrated between satellites?

The JSC noted that the importance of this calibration issue has been recognised by GCOS and the former WCRP satellite working group, leading to the “reprocessing project” now proposed under WOAP.

Analysis and modelling of patterns of climate change and variability are cross-cutting issues with the WCRP and are being examined within several of the core projects. These are also key issues within the COPES framework, and therefore prompt a question on how to foster desirable collaborative activities:

• How should SPARC work with CLIVAR on “modes of atmospheric variability” and how they will change in a changing climate (and thereby
respond to a COPES priority)?

The JSC strongly encouraged joint SPARC and CLIVAR activities on “modes of atmospheric variability” and their change in a changing climate and was pleased that this topic is included in joint CLIVAR/SPARC session at the upcoming AMS meeting in June. The ideas exchanged there could be used to plan a joint SPARC/CLIVAR Workshop on Stratosphere-Troposphere coupling and modes of variability for early 2006, the scope also to be guided by the discussions at the SPARC SSG meeting.

A number of papers and posters were presented at the Third SPARC General Assembly dealing with key processes in the tropopause transition layer (TTL) using combinations of observational and modelling approaches. Use of cloud resolving models (CRM) is proving to be an innovative and potentially powerful approach to studying key processes within the TTL. Extensive use and analysis of the performance of CRMs for tropospheric applications has been carried out in the context of the GEWEX Cloud System Study and this suggests another avenue for fruitful collaborations within the WCRP:

• Should SPARC partner with GEWEX on a new initiative to exploit cloud resolving models to understand processes in the tropopause transition layer?

The JSC encouraged partnering of SPARC and GEWEX to develop a new initiative to exploit cloud resolving models to understand processes in the tropopause transition layer. The Pan-GCSS workshop in Athens provides an opportunity to begin development of this initiative.

An outcome of the SPARC Aerosol Assessment Project (ASAP) has been the development of a number of valuable data sets. The potential importance (and uncertainty) of the radiative effects of aerosols is widely known. However, the sensitivity of radiative transfer codes to the treatment of aerosols remains a potentially important source of uncertainty suggesting the question:

• Should SPARC partner with GEWEX to initiate an intercomparison of how aerosols are treated in radiative transfer codes (with IPCC in mind)?

The JSC also encouraged partnering of SPARC and GEWEX on issues pertaining to the radiative effects of aerosols. A merger of aerosol data sets is needed and a comparison of the treatment of aerosols in radiative transfer codes should be carried out.

Evaluating the influences of solar variability on climate is important for understanding climate change. A goal of the joint SPARC-CAWSES activity on this topic is to elucidate the effects of solar variability on atmospheric composition, for example on ozone. However the effect of solar variability on the radiation budget of the whole atmosphere and the surface and its impact on the oceans and cryosphere is of broader interest and has been regarded as an important factor in modelling and evaluation of climate change. The effects of changes in atmospheric composition are not addressed in most GCMs and this may be an important shortcoming. The question for the JSC prompted by this issue is:

• What should SPARC do and how should we work with WGCM (with IPCC in mind)?

In regard to solar forcing WGCM has focused on the radiative effects of long term variations in solar forcing at the top of the atmosphere (TOA) in the absence of directly attributable changes in atmospheric composition.

The JSC recommended that SPARC should work with WGCM in updating TOA solar forcing data while continuing to pursue its current interest and activities in regard to the effects of solar forcing variations on atmospheric composition.

Data Assimilation issues are important for SPARC for several reasons. There is now a wealth of stratospheric chemical data available from satellites. Stratospheric analyses are now being produced by major operational weather prediction centres and these have been used in off line chemical transport models. Some of the presentations given in the SPARC General Assembly highlighted encouraging developments as well as challenges associated with issues of bias, noise, and inaccuracies inherent in transport algorithms. The questions posed to the JSC in this regard were the following:

• Should the SPARC Working Group on Data Assimilation (WGDA) combine with activity in the Working Group on Numerical Experimentation (WGNE)?
• What can the SPARC WGDA do for the WCRP Observations and Assimilation Panel (WOAP)?

The issue of the cooperation between the SPARC WGDA, WGNE, and WOAP was left for later consideration. A variety of further actions need to be considered. Both of the SPARC presentations were very well received by the JSC. The consensus was that they were very timely in highlighting
key issues for the WCRP as a whole and posing clear questions for discussion.

Reference: Austin, J. et al. Uncertainties and assessments of chemistry-climate models of the stratosphere. Atmos. Chem. Phys., 3(1), 1-27, 2003.

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