Impacts of land surface processes on the South American Monsoon System simulations: A GCM study

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Thursday, 21 January 2010: 12:00 PM
B216 (GWCC)
Hsi-Yen Ma, Univ. of California, Los Angeles, CA; and C. R. Mechoso, Y. Xue, H. Xiao, C. M. Wu, and F. De Sales

This research examines the impact of land surface processes on the climatology of the South American Monsoon System (SAMS). Our methodology is based on the comparison between observation datasets and simulations by the UCLA Atmospheric General Circulation Model (AGCM) coupled to either the Simplified Simple Biosphere Model (SSiB) or a simple land surface model. The SSiB allows for consideration of vegetation biophysical process effects.

Several significant improvements are found in the simulation when SSiB is included. The most notable improvement is at the lee of the Andes, where including SSiB results in a more realistic low-level southward flow that connects the sub-tropics with the extra-tropics. This is due to a better representation of the Chaco Low position, and more realistic surface heat fluxes. The partition between the latent and sensible heat fluxes (Bowen Ratio) is also more realistic. The monsoonal precipitation including convection in central Amazonia and the South Atlantic Convergence Zone is also more realistic. In particular, the amount and distribution of precipitation in central Amazonia is improved. The overestimation of convection is reduced and the precipitation bias is reduced up to 70%.