A land-atmosphere interaction theory for the tropical deforestation problem

Ning Zeng and J. David Neelin
J. Climate, 12, 857-872, 1999.

Paper (PDF 185Kb)
© Copyright 1999 by the American Meteorological Society.

Abstract. A theoretical framework is developed in understanding the mechanisms and processes determining the response of the land-atmosphere to tropical deforestation. The analytical approach is made possible by simplifications in the vertical from the quasi-equilibrium moist convective closure, and in the horizontal from the dynamical temperature homogenization process. The theory emphasizes the energy and water balance. It highlights the interaction among processes of moist convection, cloud, radiation and surface hydrology while each individual process is simplified.

Results from a wet-season surface albedo change case compare well with a recent RCCM2/BATS simulation, with the theory depicting the mechanisms and roles of the intertwining processes. The zero surface energy flux condition, due to the small heat capacity of the land, makes land-atmosphere interaction distinctly different from ocean-atmosphere interaction. Consequently, land surface temperature is largely a response to the energy and water balance, rather than a forcing as in the case of sea surface temperature. This imposes a constraint on the sensitivity to the details of surface energy partitioning. The precipitation has a significant decrease, initiated by ground radiative forcing as increased surface albedo reflects more solar radiation into space. A positive feedback by moisture convergence is essential for this tendency, with another positive feedback from reduced evaporation providing further enhancement. These are opposed by a negative feedback due to the reduced magnitude of negative cloud radiative forcing as cloud cover decreases. This sheds light on the higher sensitivity in some GCM studies with prescribed clouds. The cloud radiative forcing also has a negative feedback on the initial cooling tendency in ground temperature. Sensitivities of precipitation and ground temperature changes to individual processes are found to depend on the reference state parameter values, implying a sensitivity of anomaly response to simulated climatology for GCMs. The analysis here also serves as an example of the tight coupling between convection, large-scale atmospheric dynamics and land processes in the tropical land-atmosphere system.

Citation. Zeng, Ning, and J. D. Neelin, 1999: A land-atmosphere interaction theory for the tropical deforestation problem. J. Climate, 12, 857-872.

Acknowledgements. This work was supported in part by National Science Foundation grant ATM-9521389 and National Oceanographic and Atmospheric Administration grant NA46GP-0244.

© Copyright 1999 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be "fair use" under Section 107 of the U.S. Copyright Act September 2010 Page 2 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS's permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyrights@ametsoc.org.