Coupled convective modes in the tropics and intraseasonal oscillation

One of the great questions in tropical meteorology that has emerged during the last decade revolves around the vertical scales of motion associated with intraseasonal variability. Equivalent depths matching the vertical scale of deep large-scale convection are order 200-300m. However, coupled convective modes appear to match much smaller equivalent depths. Either the theory is incorrect, the problem is ill-posed or the tropics has to be described as a two-scale phenomena. We approach each of these issues from a theoretical and modeling perspective.

We use a multi-layer dry spectral model to study the response of the tropical atmosphere to a variety of spatial and temporal scales of forcing. In a second set of experiments, the WRF model in tropical strip mode is used. Differences in the forced modes are discussed, and special attention is given to the vertical structure that develops. A critical element appears to be the scale of the horizontal and vertical scale forcing. The experiments also allow us to test the Roundy-Frank hypothesis that the Andes and the East African highlands are important in the initiation and character of intraseasonal variability.