HR: 09:00h
AN: A31D-04    [Abstracts]
TI: Surface convergence and vertical motion profiles in the central-eastern Pacific Intertropical Convergence Zone: why is the convection so "bottom-heavy?"
AU: * Back, L
EM: larissa@atmos.washington.edu
AF: Dept. of Atmospheric Sciences University of Washington, Box 351640, Seattle, WA 98103, United States
AU: Bretherton, C
EM: breth@atmos.washington.edu
AF: Dept. of Atmospheric Sciences University of Washington, Box 351640, Seattle, WA 98103, United States
AB: Recent work has shown that in parts of the eastern Pacific ITCZ, large-scale vertical motion profiles are "bottom- heavy" with strong boundary-layer horizontal convergence, maximum vertical motion around 850mb, and divergence above. This contrasts with rainy regions over the western Pacific, where boundary-layer horizontal convergence is weak and mean horizontal convergence extends to above 400mb. Thus, for a given time-mean conditional instability, e.g. as measured by the difference of boundary-layer and mid-tropospheric moist static energy (MSE), the convection tends to be more bottom-heavy where there is strong boundary-layer convergence. Our ultimate goal is to explain this correlation using column MSE budget analysis, but a preliminary step is to see if we can explain the climatological pattern of boundary-layer convergence across the Pacific with a simple model. We use a linear mixed layer model (Stevens et al. 2002) to diagnose the extent to which observed surface convergence can be explained by SST-driven pressure gradients and friction. The model is forced with 850mb horizontal winds and pressure gradients from the ERA40 reanalysis. We find that differences between surface convergence in the east and west Pacific are predominantly associated with boundary layer temperature gradients and SST, not deeper tropospheric processes.
DE: 3307 Boundary layer processes
DE: 3314 Convective processes
DE: 3367 Theoretical modeling
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly