Barnett, T. P., K. Arpe, L. Bengtsson, M. Ji and A. Kumar,
1997: Potential Predictability and AMIP implications of midlatitude
climate variability in two general circulation models. Journal of Climate,10,
2321-2322.
Ensembles of extended Atmospheric Model Intercomparison Project (AMIP)
runs from the general circulation models of the National Centers for Environmental
Prediction (formerly the National Meteorological Center) and the Max-Planck
institute (Hamburg, Germany) are used to estimate the potential predictability
(PP) of an index of the Pacific-North America (PNA) mode of climate change.
The PP of this pattern in "perfect'' prediction experiments is 20-25 %
of the index's variance. The models, particularly that from MPI, capture
virtually all of this variance in their hindcasts of the winter PNA for
the period 1970-93.
The high levels of internally generated model noise in the PNA simulations
reconfirm the need for an ensemble averaging approach to climate prediction.
This means that the forecasts ought to be expressed in a probabilistic
manner It is shown that the models' skills are higher by about 50% during
strong SST events in the tropical Pacific, so the probabilistic forecasts
need to be conditional on the tropical SST.
Taken together with earlier studies, the present results suggest that
the original set of AMIP integrations (single 10-yr runs) is not adequate
to reliably test the participating models' simulations of interannual climate
variability in the midlatitudes.