Climate Systems Interaction Group

Reduction of tropical land region precipitation variability via transpiration

Jung-Eun Lee, Benjamin R. Lintner, J. David Neelin, Xianan Jiang, Pierre Gentine, C. Kevin Boyce, Joshua B. Fisher, J. Taylor Perron, Terence L. Kubar, Jeonghoon Lee, and John Worden

Geophys. Res. Lett., 39, L19704, doi:10.1029/2012GL053417.

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Abstract Tropical rainforests are known to exhibit low intraseasonal precipitation variability compared with oceanic areas with similar mean precipitation in observations and models. In the present study, the potential role of transpiration for this difference in precipitation variability is investigated using the National Center for Atmospheric Research (NCAR) atmospheric general circulation model. Comparing model results with and without transpiration shows that in the absence of transpiration, mean precipitation decreases as may be expected. However the incidence of both higher daily total column water and more intense precipitation increases without transpiration; consequently the variability of precipitation increases substantially. These results can be understood in terms of the complex interplay of local near- surface and remote moist dynamical processes with both local positive (boundary-layer drying) and large-scale negative (increased large-scale convergence) feedbacks when transpiration is disabled in the model. It is also shown that surface turbulent fluxes over tropical rainforests are highly correlated with incoming solar energy but only weakly correlated with wind speed, possibly decoupling land precipitation from large-scale disturbances like Madden-Julian Oscillation.

Citation Reduction of tropical land region precipitation variability via transpiration. Lee, J.-E., B. R. Lintner, J. D. Neelin, X. Jiang, P. Gentine, C. K. Boyce, J. B. Fisher, J. T. Perron, T. L. Kubar, J. Lee, and J. Worden. Geophys. Res. Lett., 39, L19704, doi:10.1029/2012GL053417.

Acknowledgments. The authors thank I.Held and R. Pierrehumbert for their encouragement and A. Sobel, H. -S. Park and anonymous reviewers for reviewing earlier versions of this paper. The work described here is performed at the Jet Propulsion Laboratory, California Institute of Technology under contracts from the National Aeronautics and Space Administration. BRL acknowledges support from National Science Foundation (NSF) grant AGS-1035968, JDN acknowledgment to NSF AGS-1102838, and PG acknowledges support from NSF AGS-1035843.