On the Equality Assumption of Latent and Sensible Heat Energy Transfer Coefficients of the Bowen Ratio Theory for Evapotranspiration Estimations: Another Look at the Potential Causes of Inequalities

Irmak, Suat; Kiliç, Ayşe; Chatterjee, Sumantra

doi:10.3390/cli2030181

Cited by 7 publications

(5 citation statements)

References 30 publications

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“…It is possible that the large biases observed in the BR method could be related to the inequality of the eddy diffusivities for temperature (K H ) and water vapour (K V ) that have been suggested by various studies (e.g. Blad and Rosenberg, 1974;Irmak et al, 2014), but evaluation of this hypothesis was outside of the scope of this study. The BR method has the benefit of providing turbulent fluxes without the need for making turbulence measurements or estimating the atmospheric stability and snow surface roughness.…”

Section: Limitations Of Methods For Determining Surface Sublimationmentioning

confidence: 66%

Comparison of methods for quantifying surface sublimation over seasonally snow‐covered terrain

Sexstone

Clow

Stannard

et al. 2016

Hydrological Processes

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Abstract:Snow sublimation can be an important component of the snow-cover mass balance, and there is considerable interest in quantifying the role of this process within the water and energy balance of snow-covered regions. In recent years, robust eddy covariance (EC) instrumentation has been used to quantify snow sublimation over snow-covered surfaces in complex mountainous terrain. However, EC can be challenging for monitoring turbulent fluxes in snow-covered environments because of intensive data, power, and fetch requirements, and alternative methods of estimating snow sublimation are often relied upon. To evaluate the relative merits of methods for quantifying surface sublimation, fluxes calculated by the EC, Bowen ratio-energy balance (BR), bulk aerodynamic flux (BF), and aerodynamic profile (AP) methods and their associated uncertainty were compared at two forested openings in the Colorado Rocky Mountains. Biases between methods are evaluated over a range of environmental conditions, and limitations of each method are discussed. Mean surface sublimation rates from both sites ranged from 0.33 to 0.36 mm day À1 , 0.14 to 0.37 mm day À1 , 0.10 to 0.17 mm day À1 , and 0.03 to 0.10 mm day À1 for the EC, BR, BF and AP methods, respectively. The EC and/or BF methods are concluded to be superior for estimating surface sublimation in snowcovered forested openings. The surface sublimation rates quantified in this study are generally smaller in magnitude compared with previously published studies in this region and help to refine sublimation estimates for forested openings in the Colorado Rocky Mountains.

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Section: Limitations Of Methods For Determining Surface Sublimationmentioning

confidence: 66%

Comparison of methods for quantifying surface sublimation over seasonally snow‐covered terrain

Sexstone

Clow

Stannard

et al. 2016

Hydrological Processes

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“…In reality these eddy diffusivities can be dissimilar (Irmak et al, 2014). This can cause an error (both a bias and extra noise) in the Bowen ratio as measured by the temperature and vapour pressure gradients compared to the EC Bowen ratio.…”

Section: Bowen Ratio Verificationmentioning

confidence: 99%

Technical note: Using distributed temperature sensing for Bowen ratio evaporation measurements

Schilperoort

Coenders-Gerrits

Luxemburg

et al. 2018

Hydrol. Earth Syst. Sci.

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Abstract. Rapid improvements in the precision and spatial resolution of distributed temperature sensing (DTS) technology now allow its use in hydrological and atmospheric sciences. Introduced by Euser et al. (2014) is the use of DTS for measuring the Bowen ratio (BR-DTS), to estimate the sensible and latent heat flux. The Bowen ratio is derived from DTS-measured vertical profiles of the air temperature and wet-bulb temperature. However, in previous research the measured temperatures were not validated, and the cables were not shielded from solar radiation. Additionally, the BR-DTS method has not been tested above a forest before, where temperature gradients are small and energy storage in the air column becomes important.In this paper the accuracy of the wet-bulb and air temperature measurements of the DTS are verified, and the resulting Bowen ratio and heat fluxes are compared to eddy covariance data. The performance of BR-DTS was tested on a 46 m high tower in a mixed forest in the centre of the Netherlands in August 2016. The average tree height is 26 to 30 m, and the temperatures are measured below, in, and above the canopy. Using the vertical temperature profiles the storage of latent and sensible heat in the air column was calculated.We found a significant effect of solar radiation on the temperature measurements, leading to a deviation of up to 3 K. By installing screens, the error caused by sunlight is reduced to under 1 K. Wind speed seems to have a minimal effect on the measured wet-bulb temperature, both below and above the canopy. After a simple quality control, the Bowen ratio measured by DTS correlates well with eddy covariance (EC) estimates (r 2 = 0.59). The average energy balance closure between BR-DTS and EC is good, with a mean underestimation of 3.4 W m −2 by the BR-DTS method. However, during daytime the BR-DTS method overestimates the available energy, and during night-time the BR-DTS method estimates the available energy to be more negative. This difference could be related to the biomass heat storage, which is neglected in this study.The BR-DTS method overestimates the latent heat flux on average by 18.7 W m −2 , with RMSE = 90 W m −2 . The sensible heat flux is underestimated on average by 10.6 W m −2 , with RMSE = 76 W m −2 . Estimates of the BR-DTS can be improved once the uncertainties in the energy balance are reduced. However, applying, for example, Monin-Obukhov similarity theory could provide independent estimates for the sensible heat flux. This would make the determination of the highly uncertain and difficult to determine net available energy redundant.

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“…One drawback of the DTS based Bowen ratio, is the assumption that the eddy diffusivity of heat and water vapour are the same. In reality these eddy diffusivities can be dissimilar (Irmak et al, 2014). This can cause an error (both a bias and extra noise) in the Bowen ratio as measured by the temperature and vapour pressure gradients compared to the eddy covariance Bowen ratio.…”

Section: Bowen Ratio Verificationmentioning

confidence: 99%

Technical note: using Distributed Temperature Sensing for Bowen ratio evaporation measurements

Schilperoort¹,

Coenders-Gerrits²,

Luxemburg³

et al. 2017

Preprint

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Abstract. Rapid improvements in the precision and spatial resolution of Distributed Temperature Sensing (DTS) technology now allows its use in hydrological and atmospheric sciences. Introduced by Euser [Hydrol. Earth Syst. Sci., 18, 2021–2032 (2014)] is the use of DTS for measuring the Bowen ratio (BR-DTS), to estimate the sensible and latent heat flux. The Bowen ratio is derived from DTS measured vertical profiles of the air temperature and wet-bulb temperature. However, in previous research the measured temperatures were not validated, and the cables were not shielded from solar radiation. Additionally, the BR-DTS method has not been tested above a forest before, where temperature gradients are small and energy storage in the air column becomes important. In this paper the accuracy of the wet-bulb and air temperature measurements of the DTS are verified, and the resulting Bowen ratio and heat fluxes are compared to eddy covariance data. The performance of BR-DTS was tested on a 46 m high tower in a mixed forest in the centre of the Netherlands in August 2016. The average tree height is 26 to 30 m, and the temperatures are measured below, in, and above the canopy. Using the vertical temperature profiles the storage of latent and sensible heat in the air column was calculated. We found a significant effect of solar radiation on the temperature measurements, leading to a deviation of up to 3 K. By installing screens, the error caused by sunlight is reduced to under 1 K. Wind speed seems to have a minimal effect on the measured wet-bulb temperature, both below and above the canopy. After a simple quality control, the Bowen ratio measured by DTS correlates well with eddy covariance (EC) estimates (r2 = 0.59). The average energy balance closure between BR-DTS and EC is good, with a mean underestimation of 3.4 W m−2 by the BR-DTS method. However, during daytime the BR-DTS method overestimates the available energy, and during night-time the BR-DTS method estimates the available energy to be more negative. This difference could be related to the biomass heat storage, which is neglected in this study. The BR-DTS method overestimates the latent heat flux on average by 18.7 W m−2, with RMSE = 90 W m−2. The sensible heat flux is underestimated on average by 10.6 W m−2, with RMSE = 76 W m−2. Estimates of the BR-DTS can be improved once the uncertainties in the energy balance are reduced. However, applying e.g. Monin-Obukhov similarity theory could provide independent estimates for the sensible heat flux. This would make the determination of the highly uncertain and difficult to determine net available energy redundant.

show abstract

On the Equality Assumption of Latent and Sensible Heat Energy Transfer Coefficients of the Bowen Ratio Theory for Evapotranspiration Estimations: Another Look at the Potential Causes of Inequalities

Cited by 7 publications

References 30 publications

Comparison of methods for quantifying surface sublimation over seasonally snow‐covered terrain

Comparison of methods for quantifying surface sublimation over seasonally snow‐covered terrain

Technical note: Using distributed temperature sensing for Bowen ratio evaporation measurements

Technical note: using Distributed Temperature Sensing for Bowen ratio evaporation measurements

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