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Reflections on the surface energy imbalance problem

Leuning, Ray ; van Gorsel, Eva ; Massman, William J. ; Isaac, Peter R.

Agricultural and forest meteorology, 2012-04, Vol.156, p.65-74 [Periódico revisado por pares]

Amsterdam: Elsevier B.V

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  • Título:
    Reflections on the surface energy imbalance problem
  • Autor: Leuning, Ray ; van Gorsel, Eva ; Massman, William J. ; Isaac, Peter R.
  • Assuntos: Advective flux divergence ; Agricultural and forest climatology and meteorology. Irrigation. Drainage ; Agronomy. Soil science and plant productions ; air ; Biological and medical sciences ; biomass ; eddy covariance ; Eddy covariance flux measurements ; energy balance ; Energy balance closure ; Fundamental and applied biological sciences. Psychology ; General agronomy. Plant production ; heat transfer ; humidity ; Micrometeorology ; radiometers ; soil ; temperature profiles
  • É parte de: Agricultural and forest meteorology, 2012-04, Vol.156, p.65-74
  • Notas: http://dx.doi.org/10.1016/j.agrformet.2011.12.002
  • Descrição: ► Three factors contributing to the lack of energy closure in micrometeorological measurements are identified. ► Incorrect measurements of energy storage in soil and biomass causes hysteresis in half-hourly measurements. ► Incorrect co-ordinate rotation causes u′T′ covariance to contaminate w′T′ covariance. ► Incorrect measurement of net radiation on non-horizontal surfaces. The ‘energy imbalance problem’ in micrometeorology arises because at most flux measurement sites the sum of eddy fluxes of sensible and latent heat (H+λE) is less than the available energy (A). Either eddy fluxes are underestimated or A is overestimated. Reasons for the imbalance are: (1) a failure to satisfy the fundamental assumption of one-dimensional transport that is necessary for measurements on a single tower to represent spatially-averaged fluxes to/from the underlying surface, and (2) measurement errors in eddy fluxes, net radiation and changes in energy storage in soils, air and biomass below the measurement height. Radiometer errors are unlikely to overestimate A significantly, but phase lags caused by incorrect estimates of the energy storage terms can explain why H+λE systematically underestimates A at half-hourly time scales. Energy closure is observed at only 8% of flux sites in the La Thuile dataset (http://www.fluxdata.org/DataInfo/default.aspx) with half-hourly averages but this increases to 45% of sites using 24h averages because energy entering the soil, air and biomass in the morning is returned in the afternoon and evening. Unrealistically large and positive horizontal gradients in temperature and humidity are needed for advective flux divergences to explain the energy imbalance at half-hourly time scales. Imbalances between H+λE and A still occur in daily averages but the small residual energy imbalances are explicable by horizontal and vertical advective flux divergences. Systematic underestimates of the vertical heat flux also occur if horizontal u′T′ covariances contaminate the vertical w′T′ signal due to incorrect coordinate rotations. Closure of the energy balance is possible at half-hourly time scales by careful attention to all sources of measurement and data processing errors in the eddy covariance system and by accurate measurement of net radiation and every energy storage term needed to calculate available energy.
  • Editor: Amsterdam: Elsevier B.V
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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