Ryan Maue has alerted us to a new paper
Dawson A., T. N. Palmer and S. Corti: 2012: Simulating Regime Structures in Weather and Climate Prediction Models. Geophyscial Research Letters. doi:10.1029/2012GL053284 In press.
This paper further documents the gross inadequacies of the CMIP5 model runs as I have summarized, for example, in my posts
See also my post on a 2008 paper by Tim Palmer
and my BAMS comment on his paper (and a related one by Jim Hurrell)
Pielke Sr., R.A., 2010: Comments on “A Unified Modeling Approach to Climate System Prediction”. Bull. Amer. Meteor. Soc., 91, 1699–1701, DOI:10.1175/2010BAMS2975.1,
The abstract of the Dawson et al 2012 GRL paper reads [highlight added]
It is shown that a global atmospheric model with horizontal resolution typical of that used in operational numerical weather prediction is able to simulate non-gaussian probability distributions associated with the climatology of quasi-persistent Euro-Atlantic weather regimes. The spatial patterns of these simulated regimes are remarkably accurate. By contrast, the same model, integrated at a resolution more typical of current climate models, shows no statistically significant evidence of such non-gaussian regime structures, and the spatial structure of the corresponding clusters are not accurate. Hence, whilst studies typically show incremental improvements in first and second moments of climatological distributions of the large-scale flow with increasing model resolution, here a real step change in the higher-order moments is found. It is argued that these results have profound implications for the ability of high resolution limited-area models, forced by low resolution global models, to simulate reliably, regional climate change signals.
Examples of key excerpts read
This paper presents a study of the ability of a state-of-the-art global atmospheric model, integrated in atmosphere-only mode at two different horizontal resolutions representative of NWP and climate models, to simulate Euro-Atlantic regime structures as found in reanalysis datasets. It is shown that whilst the NWP resolution model simulates the regimes well, the same model integrated at climate resolution has no statistically significant regimes at all.
This study supports the growing recognition that there is no more complex problem in computational science than that of simulating climate, and next generation climate simulators should be developed at current NWP resolutions – the need for Earth System complexity and ensemble capability notwithstanding.
We have shown that a low resolution atmospheric model, with horizontal resolution typical of CMIP5 models, is not capable of simulating the statistically significant regimes seen in reanalysis, yet a higher resolution configuration of the same model simulates regimes realistically. This result suggests that current projections of regional climate change may be questionable. This finding is also highly relevant to regional climate modelling studies where lower resolution global atmospheric models are often used as the driving model for high resolution regional models. If these lower resolution driving models do not have enough resolution to realistically simulate regimes, then then boundary conditions provided to the regional climate model could be systematically erroneous. It is therefore likely that the embedded regional model may represent an unrealistic realization of regional climate and variability.
This is a very convincing refutation of the claims in the Mears et al 2012 paper
Linda O. Mearns, Ray Arritt, Sébastien Biner, Melissa S. Bukovsky, Seth McGinnis, Stephan Sain, Daniel Caya, James Correia, Jr., Dave Flory, William Gutowski, Eugene S. Takle, Richard Jones, Ruby Leung, Wilfran Moufouma-Okia, Larry McDaniel, Ana M. B. Nunes, Yun Qian, John Roads, Lisa Sloan, Mark Snyder, 2012: The North American Regional Climate Change Assessment Program: Overview of Phase I Results. Bull. Amer.Met Soc. September issue. pp 1337-1362.
that I posted on in
“The North American Regional Climate Change Assessment Program: Overview of Phase I Results” By Mearns Et Al 2012 – An Excellent Study But It Overstates Its Significance In The Multi-Decadal Prediction Of Climate
As a final comment, the Dawson et al 2012 also confirms what I wrote in a paper in 1991
Pielke, R.A., 1991: Overlooked scientific issues in assessing hypothesized greenhouse gas warming. Environ. Software, 6, 100-107.
It is the recommendation, as I wrote in that paper with the title
INABILITY FOR GCM MODELS TO PROPERLY RESOLVE THE EVOLUTION OF EXTRATROPICAL AND TROPICAL CYCLONES DUE TO THEIR POOR SPATIAL RESOLUTION
with the text
The horizontal grid spacing of general circulation models is around 400 km. As shown by Pielke (1984), as least four grid increments are required to reasonably represent an atmospheric feature, thus this grid resolution would only permit features 1600 km or larger to be reasonably represented in the models, Since extratropical cyclones often are observed to have horizontal wavelengths as small as 500 km or so, they are poorly represented in these models, Since these features provide the major physical mechanism for the exchange of heat, moisture, and momenlum between the subtropics and the polar regions, the inability of GCM representations to adequately represent these exchanges is a serious shortcoming. Tropical cyclones, which also provide an important mechanism for exchanges between the tropics and higher latitude is even more poorly represented since its scales of important physical processes includes the eye wall which can be tens of kilometers in radial size. Pielke (1988) discusses this shortcoming further.
Pielke, R.A., 1984: Mesoscale meteorological modeling. Academic Press, New York, N.Y., 612 pp.
Pielke, R.A., 1988: Evaluation of climate change using numerical models. In “Monitoring Climate for the Effects of Increasing Greenhouse Gas Concentrations. Proceedings of a Workshop”. R.A.
Pielke and T. Kittel, Eds., Cooperative Institute for Research in lhe Almosphere (CIRA),