The results indicate the following. 1) There are problems for almost
all the models in capturing the seasonal variation of the precipitation
over the eastern United States. The models typically overemphasize the
summer/spring rainfall amounts. The PC analysis indicates that many of
the models tend to extend the precipitation regime typical of the central
United States too far to the east, resulting in a precipitation maxima
occurring in the summer for the eastern region. 2) The seasonal variation
of the West Coast is handled with the greatest fidelity. This result cuts
across all the models and may be attributable to the fact the SST forcing
is specified and common to all the simulations. The common SST forcing
is apparently a dominant factor in determining this region's precipitation
climatology. 3) On the space scales of the regions selected, there is little
consistent evidence that points to any specific model feature as a predictor
of model performance. None of the obvious candidates such as horizontal
resolution, convective closure schemes, or land surface schemes are reliable
discriminators of a model's ability to simulate precipitation. 4) For one
smaller subregion centered over Arizona, chosen because of the dominance
of the semiannual cycle, there is evidence that increased horizontal resolution
has an effect. For this inter mountain region the higher-resolution models
as a whole do better than the low resolution models. However, even in this
case there is enough variation among the individual simulations to obscure
the conclusion that increased horizontal resolution is a necessary or sufficient
quality to produce a reliable simulation. 5) The models tend to have less
interannual variation than the observations with more variance being explained
by the leading (annual cycle) PC, whereas the observations have a less
peaked spectrum.