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  • Stowasser, M., and K. Hamilton, 2006: Relationships between cloud radiative forcing and local meteorological variables compared in observations and several global climate models. J. Climate, 19, 43444359, DOI: 10.1175/JCLI3875.1.

The relations between local monthly-mean shortwave cloud radiative
forcing and aspects of the resolved-scale meteorological fields
are investigated in hindcast simulations performed with 12 of the
global coupled models included in the model intercomparison conducted
as part of the preparation for IPCC Fourth Assessment Report (AR4).
In particular, the connection of the cloud forcing over tropical
and subtropical ocean areas with resolved midtropospheric vertical
velocity and with lower level relative humidity are investigated
and compared among the models. The model results are also compared
with observational determinations of the same relationships
using satellite data for the cloud forcing and global reanalysis
products for the vertical velocity and humidity fields.
In the analysis the geographical variability in the long-term
mean among all gridpoints and the interannual variability of
the monthly-mean at each gridpoint are considered separately.
The shortwave cloud radiative feedback (SWCRF) plays a crucial role
in determining the predicted response to large-scale climate
forcing (such as from increased greenhouse gas concentrations),
and it is thus important to test how the cloud representations in
current climate models respond to unforced variability.

Overall there is considerable variation among the results for the
various models, and all models show some substantial differences
from the comparable observed results. The most notable deficiency
is a weak representation of the cloud radiative response to
variations in vertical velocity in cases of strong ascending or
strong descending motions. While the models generally perform
better in regimes with only modest upward or downward motions,
even in these regimes there is considerable variation among the
models in the dependence of SWCRF on vertical velocity. The
largest differences between models and observations when SWCRF
values are stratified by relative humidity are found in either
very moist or very dry regimes. Thus the largest errors in the
model simulations of cloud forcing are prone to be in the western
Pacific warm pool area, which is characterized by very moist
strong upward currents, and in the rather dry regions where the
flow is dominated by descending mean motions.


Last Updated: 2007-05-31

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