CAPT is a joint
project of the
Atmospheric Radiation Measurement (
ARM)
and Climate Change Prediction
Programs (
CCPP)
of the U.S. Department of Energy's Office of Science/Biological and
Energy Research (
BER).
We are using analyses of global weather from numerical weather
prediction (NWP) centers, in conjunction with field observations
such as those provided by ARM, to evaluate parameterizations of
sub-gridscale processes in global climate models.
Simply
stated, we run realistically initialized climate models in
forecast mode to determine their initial drift from the NWP analyses
and/or from the available field data,
thereby gaining insights
on model parameterization deficiencies.
See our
publications
for further details on the work of the CAPT project.
- Origins
From the
1999 Report of the
Working Group on Numerical Experimentation (WGNE) on
"Transpose AMIP":
"WGNE is continuing to develop the concept
of what is termed a
"Transpose AMIP", in which climate models would be run in NWP mode, and
the evolution of the forecast and of various variables examined, as
well as the behaviour of parameterizations before the forecast state
diverges too far from the truth. More specifically, predicted variables
will be compared with values from reanalyses over regions where these
variables are known to be correct from comparison with observations
(i.e. data rich areas over the US and/or Europe) in forecasts of only a
few days during which the state may be considered 'correct'. The
intention is to try and learn why there are model errors, rather than
just what the errors are. WGNE recognized that the initialization and
spin up of the forecasts were likely to be critical aspects of whether
useful results could be obtained, especially in trying to assess model
treatments of cloud and radiation. Nevertheless, a pilot project is
being undertaken at NCAR with the CCM model using initial data provided
by ECMWF (which then have to be interpolated to the CCM grid)."
and from the 1999-2009
Plan of the European Centre for Medium-Range Weather Forecasts (ECMWF):
"One can have confidence in simulated
climate scenarios only if one
has confidence in the physical formulations and feed-back loops of the
GCMs. A strong case could be made that every GCM should be equipped
with a data assimilation system, so that one can diagnose its
performance with field experiment data and in medium- and
extended-range forecasts."
- Tony Hollingsworth
Methodology
The CAPT
protocol (see schematic) is
analagous to a common NWP approach for
development of forecast models. It is also potentially
useful for
diagnosing parameterization problems that may produce systematic model
errors on climate time scales . Our goal is to adapt this NWP-inspired
technique for its practical application in the development cycles of
climate models (Phillips
et al. 2004).
