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  • Author or Editor: Piers J. Sellers x
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Piers J. Sellers
,
W. James Shuttleworth
,
Jeff L. Dorman
,
Amnon Dalcher
, and
John M. Roberts

Abstract

This paper describes the operation and calibration of the simple biosphere model (SiB) of Sellers et al. using micrometeorological and hydrological measurements taken in and above tropical forest in the central Amazon basin. The paper provides:

(i) an overview of the philosophy, structure and assumptions used in the model with particular reference to the tropical forest;

(ii) a review of the experimental systems and procedures used to obtain the field data; and

(iii) a specification of the physiological parameterization required in the model to provide an adequate average description of the data.

In the course of this study, it was found that some of the existing literature on stomatal behavior for tropical tropical species is inconsistent with the observed behavior of the complete canopy in Amazonia and that the rainfall interception store of the canopy is considerably smaller than originally specified in SiB. Also the turbulent transfer model used in SiB was modified to account for the effects of height-varying foliage density. Finally, it was demonstrated that there is a distinct annual cycle in the biophysical properties of the forest canopy which influences the partitioning of energy into sensible and latent heat fluxes.

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Yongkang Xue
,
Heidi G. Bastable
,
Paul A. Dirmeyer
, and
Piers J. Sellers

Abstract

The simplified Simple Biosphere model (SSiB) has been validated using observed meteorological, turbulent flux, and vegetation property data from the Anglo-Brazilian Amazonian Climate Observation Study (ABRACOS) over a forest clearing site. The results show that SSiB is able to simulate the observed fluxes realistically. The differences between the simulated and observed latent and sensible heat fluxes are less than 10 W m−2. Compared to previous deforestation experiments, the new vegetation dataset produces significantly different latent heat fluxes and surface temperatures in off-line and general circulation model (GCM) simulation. Using the new dataset the GCM simulated surface temperature is about 2 K higher, and the simulated latent heat flux is about 25 W m−2 lower than that generated using a previous dataset. These differences can be expected to result in substantially different responses in rainfall and atmosphere circulation. The parameters that are most significant in producing such large differences are leaf area index and soil properties. This study again demonstrates that to realistically assess the climatic impact of land surface degradation a realistic specification of the land surface conditions within GCMs is crucial.

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