Tuesday, 15 January 2002: 4:45 PM
Validating the Radiative and Dynamical Feedbacks in NCAR CCM3
Using seasonal and interannual signals in the equatorial SST, the radiative and dynamical feedbacks in the equatorial atmosphere are calculated using both observations and outputs from the NCAR CCM3. The results show that the positive feedback from the greenhouse effect of water vapor agrees well with that from the ERBE observations. The dynamical feedback from atmospheric transport in the model is also comparable with that from the NCEP reanalysis. However, the greenhouse effect of clouds is significantly larger than the observed while the negative feedback from the solar forcing of clouds in the model is significantly weaker. Consequently, the net atmospheric feedback--the response of the surface heat flux to the SST in the model is nearly positive while the net feedback in the observed atmosphere is strongly negative. The effect of the bias in the atmospheric feedbacks on the the coupling between the atmosphere and ocean is investigated using a box model of the equatorial ocean-atmosphere system. The results suggest that the bias in the atmospheric feedbacks can be further amplified by the coupling process--the Bjerknes positive feedback loop in particular--and result in large errors in the equilibrium SST of the coupled system.