Abstract
An analysis of the climatic feedbacks in the NCAR Community Climate Model, version 3 (CCM3) over the
equatorial Pacific cold tongue is presented. Using interannual signals in the underlying SST, the radiative and
dynamical feedbacks have been calculated using both observations and outputs from the NCAR CCM3. The
results show that the positive feedback from the greenhouse effect of water vapor in the model largely agrees
with that from observations. The dynamical feedback from the atmospheric transport in the model is also
comparable to that from observations. However, the negative feedback from the solar forcing of clouds in the
model is significantly weaker than the observed, while the positive feedback from the greenhouse effect of
clouds is significantly larger. Consequently, the net atmospheric feedback in the CCM3 over the equatorial cold
tongue region is strongly positive (5.1 W m22 K21), while the net atmospheric feedback in the real atmosphere
is strongly negative (26.4 W m22 K21). A further analysis with the aid of the International Satellite Cloud
Climatology Project (ISCCP) data suggests that cloud cover response to changes in the SST may be a significant
error source for the cloud feedbacks. It is also noted that the surface heating over the cold tongue in CCM3 is
considerably weaker than in observations. In light of results from a linear feedback system, as well as those
from a more sophisticated coupled model, it is suggested that the discrepancy in the net atmospheric feedback
may have contributed significantly to the cold bias in the equatorial Pacific in the NCAR Climate System Model
(CSM).