HR: 1340h
AN: A43B-0043    [Abstracts]
TI: The Causes of Tropical Atlantic Precipitation Biases in AGCMs: in Search of a Comprehensive Diagnosis.
AU: * biasutti, m
EM: biasutti@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Sobel, A
EM: ahs129@columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Sobel, A
EM: ahs129@columbia.edu
AF: Department of Applied Physics and Applied Mathematics, S.W. Mudd, Room 217 Columbia University 500 W 120th St, new york, NY 10027 United States
AU: Kushnir, Y
EM: kushnir@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AB: This study focuses on the biases in monthly mean Atlantic marine ITCZ (AMI) in reanalyses and AMIP-like GCM simulations. We establish a set of diagnostics that provides a comprehensive, multi-variable description of the thermodynamical and dynamical characteristics of precipitation and its response to changes in local and remote conditions. Maps, vertical profiles, and budget analysis of key variables provide a description of the large scale environment; joint probability density functions and correlation analysis document the relationship between precipitation and its local environment. Comparisons between the Atlantic and the Pacific ITCZs in each model, among different models, and between models and observations allow us to hypothesize explanations for biases in the simulation of AMI. For example, convection in CCM3 responds more strongly to surface humidity than to the integrated humidity in a deeper boundary layer. In turn, surface humidity is determined to a large extent by SST and evaporation, and not mostly by convergence. In both cases, CCM3 is at odds with observations, reanalysis products, and other models. Thus, we hypothesize that biases in the CCM3 simulation of AMI are due both to the way the convection scheme responds to its environment (i.e., the weak dependance on lower tropospheric humidity), and to the way the environment is simulated (what determines the surface humidity).
DE: 3379 Turbulence
DE: 3309 Climatology (1620)
DE: 3319 General circulation
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting