Collaborative Research: An Optimality Principle of Evaporation over the Land Surface

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Bras0309594The working hypothesis of this research is that evaporation at the earth-atmosphere interface is always maximized, given radiative energy input in a particular environment. Under the hypothesis, evaporation is uniquely determined as a result of an optimization exercise in terms of surface temperature, surface soil moisture and sensible heat flux (a measure of turbulent transport) given an energy input.Intellectual Merits:The ideas presented here will allow the independent verification of models, will lead to improved parameterization of surface hydrology and, more importantly, will provide a framework in which the sensitivity of land evaporation to changes in radiation, earth surface properties etc. could be evaluated independently of the traditional empirical models. The research strategy includes: 1. further theoretical and empirical study to include the dependence of long wave radiation on surface temperature; 2. show the lack of sensitivity of evaporation to atmospheric moisture; 3. carry out field work to test the concepts with more appropriate data sets over bare soils; 4. investigate the validity of existing evaporation models; 5. initiate the extension of the concepts to vegetated surfaces.Broader Impacts:This work represents a broad interdisciplinary collaboration between hydrologists and ecologists with theoretical and experimental expertise. The work supports unique experimental infrastructure at the University of Iowa. Undergraduate students will have the opportunities to do theoretical and field work. Several graduate students will get their masters/doctoral degrees based on their work in this proposal. All students will be encouraged and financed to present findings in professional meetings. All work will be published in the refereed literature in a timely manner. This proposal is being submitted under the umbrella of the new MIT Earth System Initiative. This research and educational effort is intended to promote the understanding of the ``body earth'' in order to define the appropriate science to develop sound sustainability policies. The Principal Investigator is one of the leaders of this initiative, a member of its executive council, and teaches one of the require courses under the initiative's freshman core alternative program: Terrascope.