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Summary of the CCMVal 2005 Workshop
on
“Process-Oriented Validation of Coupled Chemistry-Climate Models”
V. Eyring
(DLR, Germany), A. Gettelman (NCAR, USA), N.R.P. Harris (EORCU, UK), S.
Pawson
(NASA, USA), T.G. Shepherd (Univ. of Toronto, Canada), N. Butchart (Met
Office,
UK), M.P. Chipperfield (Univ. of Leeds, UK), M. Dameris (DLR, Germany),
D.W.
Fahey (NOAA, USA), P.M. de F. Forster (Univ. of Leeds, UK), P.A. Newman
(NASA,
USA), R.J. Salawitch (JPL, USA), B.D. Santer (LLNL, USA), and D.W.
Waugh (JHU, USA)
Introduction
The CCM Validation Activity for SPARC
(CCMVal) is a response to the need for consistent evaluation and
validation of
coupled chemistry-climate models (CCMs) with detailed descriptions of
the
stratosphere, which have been developed over the last 5-10 years. These CCMs provide valuable
indications of
how stratospheric ozone will evolve in the future as halogen
concentrations
decline in an atmosphere with a changing climate (e.g., WMO, 2003). The
high
complexity of CCMs requires a systematic evaluation process in order to
demonstrate that the models are representative of the atmosphere and to
quantify the uncertainty of the model results.
The first CCMVal workshop was held in
November 2003 in Grainau,
Germany,
to develop a more
comprehensive approach to CCM validation. The concept was based on
model inter-comparisons of the dynamical-radiative
state such as those within the GCM-Reality Intercomparison Project for
SPARC (GRIPS) (Pawson
et al. (Au, 2000) and on an assessment
of chemistry-climate models of the stratospherestin et al.,
2003). The strategy developed
was to identify the core processes that determine the stratospheric
state and
to select a number of diagnostics for each process within four main
categories:
dynamics, stratospheric transport, radiation, and stratospheric
chemistry and
microphysics. Processes associated with
the Upper Troposphere/Lower Stratosphere (UTLS) were also included
under these
categories. A full description of the
approach can be found in Eyring et al.
(2005). An essential part of the
strategy is that the diagnostics would evolve over time, e.g., as new
data sets
or approaches become available.
A second
CCMVal workshop was held at the National
Center for Atmospheric
Research
(NCAR), Boulder, USA, on 17 – 19 October
2005. The
goals of the workshop were to assess progress in the validation of CCMs
following the guidelines developed in the first CCMVal workshop and to
assess
how CCM model results can support upcoming UNEP/WMO and IPCC
Assessments.
Approximately 90 members of the atmospheric and climate communities
from
Europe, the United States,
Canada, Japan,
and New Zealand
attended the workshop to take stock of progress and to identify
near-term and
long-term goals within the validation framework. The
attendees included representatives from
nearly all the major stratospheric CCM groups in the world. The agenda
and a
list of participants can be found at the workshop’s website at http://www.pa.op.dlr.de/workshops/CCMVal2005/.
Main points of discussion
The
introductory session reviewed the background context for the CCMVal
activity, including WMO/UNEP and
IPCC assessments, discussed related activities in the tropospheric
climate modeling community, and emphasized the importance of
understanding uncertainties in corroborative measurements.
The central part of the workshop consisted
of oral and poster sessions on the progress made in the four main areas
of
CCMVal. The presentations and the
accompanying discussions showed that (a) good progress was being made
in the
evaluation of CCMs since the first CCMVal workshop; (b) the evaluation
needs to
be more quantitative in the future; and (c) a more detailed description
of the
individual diagnostics
is necessary in order to make the table more practical and to allow individual groups to perform the diagnostics themselves.
Some analyses compared the results of
several models with observed quantities based on model data submitted
to the
CCMVal/SCOUT-O3 database at the British Atmospheric Data Centre (BADC),
others
were ‘ad hoc’ inter-comparisons, while still other studies described
evaluations of single models, often based on new diagnostics that they
had
developed. While all approaches have
their merits, the advantages and need for a central data archive to
allow
consistent analyses between models was clearly identified during the
meeting.
It is important to maximize the resources
available to CCM groups. Most of the
meeting was spent discussing how to ensure that CCMs can be evaluated
better
and more consistently in the future, given the finite resources
available to
the stratospheric CCM groups. Each
diagnostic was considered in turn and most were refined considerably. This was done in a number of ways. In some cases precise descriptions of each
diagnostic will be produced, specifying the method of calculation, the
measurement set to be used for comparison, providing central software
tools for
more complicated diagnostics, etc. In
others, particularly for the chemistry assessment, individuals
volunteered to
analyze data placed on the database.
The diagnostics were prioritized again
according to whether they were considered to be: 1) core,
2) important, or 3)
useful. A core
diagnostic was considered to be proven, straightforward to
calculate, and
important for illuminating the model processes.
An important diagnostic was
important, but somewhat difficult to calculate or not well defined
and
requiring additional research. Finally,
a useful diagnostic was well defined
and of importance, but only complementary to the core diagnostics.
The core, important, and useful
categorization of the diagnostics will be updated. This CCMVal process
will
allow for future diagnostics to be added to our current tables. Additional new diagnostics will be added that
illuminate key model processes. In
addition, current important and useful diagnostics will be reevaluated
in
response to modeling and research results.
In particular, considerable discussion was
devoted at the workshop to two areas of great importance where further
research
is needed to define suitable core diagnostics: UTLS transport, and
polar
chemical ozone loss. These diagnostics are currently listed as
important but it
is expected that they will evolve into core diagnostics in the future.
The
up-to-date version of the CCMVal process table will be maintained on
the CCMVal
website (http://www.pa.op.dlr.de/CCMVal/).
Future plans
Several aspects of future plans related to CCMVal
activities were
actively discussed. The plans relate to
maintaining progress and awareness with CCMVal tasks, interacting with
the
broader atmospheric sciences and climate communities, and documenting
the
progress of CCMVal. The following were
considered of high priority:
·
Presentations
at international scientific meetings. Presenting the results of
model inter-comparison activities
is
considered valuable for documenting the skill of CCMs and their
improvements,
for creating awareness of CCMVal activities and thereby entraining new
participants, and for addressing the scientific understanding issues
that have
arisen in the model inter-comparisons.
Suggested meetings are those of the European Geophysical Union
and the
American Geophysical Union.
·
Documenting
the progress of CCMVal. Progress
matrices will be set up to document the state of the evaluation of the
listed
diagnostics and the participation of individual CCM groups. Again, the up-to-date version of the progress
matrices can be found at the CCMVal website.
·
Creating
an Ensemble and Central Archive of CCM runs. A central archive of CCM model runs for the 20th
and 21st
centuries which can be used to assess model performance and to support
upcoming
WMO/UNEP and IPCC assessments has been created as part of CCMVal and
the
European Integrated Project SCOUT-O3. At some time in the future this
archive
will be made available to the community as an ‘ensemble of opportunity’.
·
CCMVal
2007 Workshop. A
third CCMVal workshop is tentatively
planned for 2007. The workshops have
been very effective at bringing together climate modelers to discuss
and plan
for evaluation and validation activities.
The workshop goals at this early stage are: (i) show analysis of
recent
model results using CCMVal diagnostics, (ii) update CCMVal model
diagnostics,
(iii) review scientific results from the 2006 UNEP/WMO Scientific
Assessment of
Ozone Depletion, (iv) form an outline and a team to write a model
evaluation
report for SPARC, and (v) make recommendations for forcing scenarios
that could
support the expected 2010 UNEP/WMO assessment.
·
SPARC
Report in 2008/2009.
A SPARC Report on CCMVal results was proposed
for the 2008/2009 time period. The
Report would be a comprehensive summary of the progress and results
obtained
from CCM inter-comparisons and the use of CCMs in the ozone and climate
assessment activities. The Report would
document the CCMVal approach and discuss the table of processes and
diagnostics
that have been developed and used over a period of years since the
inception of
CCMVal. The Report would be
peer-reviewed by the atmospheric sciences community.
·
In addition, the
possibility of
using some of the approaches developed for assessing climate models at
PCMDI
will be considered in order to make the evaluation more quantitative
and to
have a better understanding of the overall stratospheric CCM ensemble.
In summary,
good progress was made during the second CCMVal workshop.
Several people agreed to take the lead for specific diagnostics
and analyses, and it is hoped that all CCM groups will have joined in
the inter-comparison by the next CCMVal workshop in 2007 so that a more
quantitative evaluation will be reached. Participation in and comments
on CCMVal are requested from the international community. For full
details on CCMVal activities and contacts see http://www.pa.op.dlr.de/CCMVal/.
Acknowledgements
The 2005
Workshop was held under the auspices of the CCM Validation Activity for
WCRP's
(World Climate Research Programme) SPARC (Stratospheric Processes and
their
Role in Climate), the National
Center for
Atmospheric
Research (NCAR), and the National Oceanic and Atmospheric
Administration
(NOAA). We thank Andrew Gettelman, David Fahey, Christina Book and
Suzette
Milano-Schoser for the local organization and all the workshop
participants for
their valuable contributions.
References
Austin, J., et al.
Uncertainties
and assessments of chemistry-climate models of the stratosphere, Atmos. Chem. Phys., 3, 1-27, 2003.
Eyring V., et
al.
, 2005: A strategy for process-oriented validation of coupled
chemistry-climate models. Bull. Am.
Meteorol. Soc., 86, 1117–1133.
Pawson, S., et
al.
The GCM-Reality Intercomparison Project for SPARC: Scientific
Issues and
Initial Results, Bull. Am. Meteorol. Soc.,
81, 781-796, 2000.
WMO, Scientific Assessment
of Ozone Depletion: 2002, Global Ozone Research and Monitoring Project
- Report
No. 47, 498 pp, Geneva,
2003.
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