|Paw U, K.t.|
Submitted to: Boundary Layer Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2011
Publication Date: 6/27/2012
Publication URL: http://www.springerlink.com/content/6504412770325664/
Citation: Shapland, T.M., Mcelrone, A.J., Snyder, R.L., Paw U, K. 2012. Structure function analysis of two-scale Scalar Ramps. Part I: Theory and Modeling. Boundary Layer Meteorology. DOI: 10.1007/s10546-012-9742-5. Interpretive Summary: In these paired studies, we describe the theoretical basis (part 1) and practical application (part 2) of a new mathematical method to determine heat and water exchange from crop surfaces obtained from surface renewal (SR) energy balance measurements. The SR technique uses measurements of sensible (i.e. the temperature rise when an air parcel is heated) and soil heat fluxes and net irradiance at the ground or crop canopy surface to estimate latent energy exchange (i.e. heat flux from the Earth’s surface to the atmosphere associated with evaporation or transpiration of water from a crop surface). To date SR has been unable to serve as a stand-alone technique capable of describing energy exchange process above agricultural surfaces (i.e. crop fields, vineyards, orchards). The new method described here works well over bare ground and short canopies under unstable conditions, and should form the foundation for analysis over taller and more complex surfaces. The advances reported here should enable SR to become a widely used and relatively inexpensive technique for better quantifying water flux and irrigation needs for crop land across the region.
Technical Abstract: Structure functions are used to study the dissipation and inertial range scales of turbulent energy, to parameterize remote turbulence measurements, and to characterize ramp features in the turbulent field. The ramp features are associated with turbulent coherent structures, which dominate energy and mass fluxes in the atmospheric surface layer. The analysis of structure functions for indentifying the ramp characteristics is used in surface renewal methods. It is unclear how different scales of coherent structures (i.e., smaller ramps embedded in larger ramps) that are commonly observed in data influence structure function analysis. In this paper, we examine the effects of multiple ramp scales on structure functions and their analysis by using both artificially generated multi-scale ramp series and high frequency temperature observations from above bare ground and two types of short plant canopies. We used structure function lags ranging in scale from isotropic to larger than the characteristic turbulent coherent structures and special analysis of structure functions to detect different scales of coherent structures. The frequencies of the coherent structure scales increase with mean wind shear, but the size of the scales relative to one another is fairly constant. The new objective method reported here for obtaining surface renewal-based scalar exchange works well over bare ground and short canopies under unstable conditions, and should form the foundation for analysis over taller and more complex surfaces.