15B.4
Cloud Radiative Effects and Tropical Intraseasonal Variability
Sandrine Bony, Laboratoire de Meteorologie Dynamique, Paris, France; and K. A. Emanuel
Theories of tropical intraseasonal oscillations that rely on positive feedbacks between convection and the large-scale flow and/or between the surface flow and surface enthalpy fluxes generally produce disturbances that propagate eastward somewhat faster than is observed. On the other hand, recent observations show that interactions between clouds and radiation strongly modulate the radiative cooling of the tropical atmosphere. Here we investigate the role of these interactions, and more generally of radiative feedbacks associated with water vapor and cloud variations, in the intraseasonal variability of the Tropics. For this purpose, we carry out two-dimensional numerical simulations using an aqua-planet equatorial general circulation model including detailed parameterizations of cumulus convection, clouds and radiation that have been optimized using data from TOGA-COARE. This model spontaneously generates eastward propagating 30-60 day oscillations of planetary scale when cloud-radiation interactions are turned on, while it generates much faster oscillations when the cloud radiative forcing is turned off or kept constant. These results are analyzed and interpreted further by using a linear model of the tropical atmosphere to investigate how the radiative feedbacks affect the growth rate and the phase speed of unstable modes of the tropical atmosphere.
Session 15B, Intraseasonal variability (Parallel with Sessions 15A and 15D)
Thursday, 2 May 2002, 4:00 PM-5:15 PM
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