Relative Efficiency of Surface Energy Partitioning Over Different Land Covers.
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Date
2013-01
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Abstract
Aims: In this paper, we aim to assess different parameterization schemes for quantifying
the surface energy portioning process, in particular, the latent and sensible heat fluxes,
and their applicability to various surface cover types.
Study Design: This study intercompares theoretical models that predict the relative
efficiency of the latent heat (evapotranspiration) with respect to the sensible heat flux.
Model predictions are compared with field measurements over surface covers with
different physical characteristics and soil water availability.
Place and Duration of Study: This study was carried out at the Arizona State University,
Tempe, AZ, between August 2012 and December 2012.
Methodology: Three theoretical models for prediction of the relative efficiency of the
latent heat were investigated, based on the lumped heat transfer (Priestley), the linear
stability analysis (LSA) and the maximum entropy principle (MEP), respectively. Model
predictions were compared against field measurements over three different land cover
types, viz. water, grassland and suburban surfaces. An explicit moisture availability
parameter β is incorporated in the MEP model, to facilitate direct comparison against the
LSA and field measurements. Standard post-processing and quality control were applied to field measured turbulent fluxes using the eddy-covariance (EC) technique. To be
consistent with the premise of all theoretical models, diurnal series of sensible and latent
heat fluxes were filtered such that only data points under convective conditions were
selected.
Results: Among all three models, the application of Priestley model is restricted to
saturated land surfaces, and generally overestimates the relative efficiency of the latent
heat for water-limited surfaces. The LSA and MEP models predict similar β ranges, i.e.,
0.05-0.3 in summer and 0.1-0.7 in winter over suburban area, and 0.1 to 0.5 over lake
surface. Over vegetated surfaces, the MEP model predicts a reasonable β range around
unity by taking transpiration into consideration, while the LSA model consistently
underestimated the relative efficiency.
Conclusion: Moisture availability plays an essential role in regulating the surface energy
partitioning process. The introduction of the moisture availability parameter enables
versatile theoretical models for latent heat (and evapotranspiration) predictions over a
wide range of land cover types. This study provides a physical insight into the
thermodynamics mechanism governing the surface energy balance, and the potential to
develop novel surface energy parameterization schemes based on the concept of relative
efficiency. The MEP model is found to have the greatest potential in terms of future
theoretical model development.
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Keywords
Relative efficiency, surface energy partitioning, Bowen Ratio, land cover, evapotranspiration, land-atmospheric interactions
Citation
Yang Jiachuan, Wang Zhi-Hua, Lee T –W. Relative Efficiency of Surface Energy Partitioning Over Different Land Covers. British Journal of Environment and Climate Change. 2013 Jan-Mar; 3(1): 86-102.