Global Model Simulation of Clouds in CMIP5 and CMIP3
Axel Lauer and Kevin Hamilton
J. Climate, in press
The Coupled Model Intercomparison
Project phase 3 (CMIP3) and 5 (CMIP5)
results allow evaluation of state-of-the art
global climate models from the world’s
major research centers circa 2005 and
2011. A major challenge is simulation of
realistic cloud fields. Figure 1 shows
observed annual mean cloud properties
and biases in the CMIP simulations
representing the late 20th century.
Fig. 1. Biases in simulated long term annual mean cloud liquid water path (top) and fractional cloud
amount (bottom). Satellite observations are shown at right, and the biases from the observations are
shown for the multimodel mean for CMIP3 (left) and CMIP5 (center).
Fig. 2. Comparison of the CMIP5
multimodel mean bias of simulated
cloud liquid water path in the full
coupled
atmosphere-ocean models
(left) and in experiments run with
prescribed observed ocean surface
temperatures (right).
Although the multi-model mean
results shown are better than the
individual model results (not shown),
they still display very large biases.
Overall the CMIP5 model results are
improved only modestly over those from
the older CMIP3 models. The simulated
biases in cloud liquid water path in fully
coupled ocean-atmosphere models and in
“AMIP” experiments with imposed
observed ocean temperatures are shown
in Figure 2. The coupled and AMIP runs
have remarkably similar biases, directly
implicating the treatments of subgridscale cloud and boundary layer processes
in the poor cloud simulations by state-ofthe-art global models.