scholarly journals Uncertainty analysis of computational methods for deriving sensible heat flux values from scintillometer measurements

2009 ◽  
Vol 2 (3) ◽  
pp. 1383-1417 ◽  
Author(s):  
P. A. Solignac ◽  
A. Brut ◽  
J.-L. Selves ◽  
J.-P. Béteille ◽  
J.-P. Gastellu-Etchegorry ◽  
...  
Keyword(s):  
Heat Flux ◽  
Classical Method ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Eddy Correlation ◽  
Time Averaging ◽  
Sensible Heat ◽  
Ratio Measurement ◽  
The Impact

Abstract. The use of scintillometers to determine sensible heat fluxes is now common in studies of land-atmosphere interactions. The main interest in these instruments is due to their ability to quantify energy distributions at the landscape scale, as they can calculate sensible heat flux values over long distances, in contrast to Eddy Correlation systems. However, scintillometer data do not provide a direct measure of sensible heat flux, but require additional data, such as the Bowen ratio (β), to provide flux values. The Bowen ratio can either be measured using Eddy Correlation systems or derived from the energy balance closure. In this work, specific requirements for estimating energy fluxes using a scintillometer were analyzed, as well as the accuracy of two flux calculation methods. We first focused on the classical method (used in standard software). We analysed the impact of the Bowen ratio according to both time averaging and ratio values; for instance, an averaged Bowen ratio (β) of less than 1 proved to be a significant source of measurement uncertainty. An alternative method, called the "β-closure method", for which the Bowen ratio measurement is not necessary, was also tested. In this case, it was observed that even for low β values, flux uncertainties were reduced and scintillometer data were well correlated with the Eddy Correlation results.

scholarly journals Uncertainty analysis of computational methods for deriving sensible heat flux values from scintillometer measurements

2009 ◽  
Vol 2 (2) ◽  
pp. 741-753 ◽  
Author(s):  
P. A. Solignac ◽  
A. Brut ◽  
J.-L. Selves ◽  
J.-P. Béteille ◽  
J.-P. Gastellu-Etchegorry ◽  
...  
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Classical Method ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Ratio Measurement ◽  
The Impact ◽  
Closure Method

Abstract. The use of scintillometers to determine sensible heat fluxes is now common in studies of land-atmosphere interactions. The main interest in these instruments is due to their ability to quantify energy distributions at the landscape scale, as they can calculate sensible heat flux values over long distances, in contrast to Eddy Covariance systems. However, scintillometer data do not provide a direct measure of sensible heat flux, but require additional data, such as the Bowen ratio (β), to provide flux values. The Bowen ratio can either be measured using Eddy Covariance systems or derived from the energy balance closure. In this work, specific requirements for estimating energy fluxes using a scintillometer were analyzed, as well as the accuracy of two flux calculation methods. We first focused on the classical method (used in standard softwares) and we analysed the impact of the Bowen ratio on flux value and uncertainty. For instance, an averaged Bowen ratio (β) of less than 1 proved to be a significant source of measurement uncertainty. An alternative method, called the "β-closure method", for which the Bowen ratio measurement is not necessary, was also tested. In this case, it was observed that even for low β values, flux uncertainties were reduced and scintillometer data were well correlated with the Eddy Covariance results. Besides, both methods should tend to the same results, but the second one slightly underestimates H while β decreases (<5%).

scholarly journals The impact of broadleaved woodland on water resources in lowland UK: II. Evaporation estimates from sensible heat flux measurements over beech woodland and grass on chalk sites in Hampshire

2005 ◽  
Vol 9 (6) ◽  
pp. 607-613 ◽  
Author(s):  
J. Roberts ◽  
P. Rosier ◽  
D. M. Smith
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Excellent Agreement ◽  
Sensible Heat Flux ◽  
Late Summer ◽  
Eddy Correlation ◽  
Sensible Heat ◽  
Flux Measurements ◽  
Shallow Soils ◽  
The Impact

Abstract. The impact on recharge to the Chalk aquifer of substitution of broadleaved woodland for pasture is a matter of concern in the UK. Hence, measurements of energy balance components were made above beech woodland and above pasture, both growing on shallow soils over chalk in Hampshire. Latent heat flux (evaporation) was calculated as the residual from these measurements of energy balances in which sensible heat flux was measured with an eddy correlation instrument that determined fast response vertical wind speeds and associated temperature changes. Assessment of wind turbulence statistics confirmed that the eddy correlation device performed satisfactorily in both wet and dry conditions. There was excellent agreement between forest transpiration measurements made by eddy correlation and stand level tree transpiration measured with sap flow devices. Over the period of the measurements, from March 1999 to late summer 2000, changes in soil water content were small and grassland evaporation and transpiration estimated from energy balance-eddy flux measurements were in excellent agreement with Penman estimates of potential evaporation. Over the 18-month measurement period, the cumulative difference between broadleaved woodland and grassland was small but evaporation from the grassland was 3% higher than that from the woodland. In the springs of 1999 and 2000, evaporation from the grassland was greater than that from the woodland. However, following leaf emergence in the woodland, the difference in cumulative evaporation diminished until the following spring.

scholarly journals Improving Computation of Sensible Heat Flux over a Water Surface Using the Variational Method

2006 ◽  
Vol 7 (4) ◽  
pp. 678-686 ◽  
Author(s):  
Zuohao Cao ◽  
Jianmin Ma ◽  
Wayne R. Rouse
Keyword(s):  
Heat Flux ◽  
Variational Method ◽  
Gradient Method ◽  
Similarity Theory ◽  
Sensible Heat Flux ◽  
Open Water ◽  
Heat Fluxes ◽  
Eddy Correlation ◽  
Sensible Heat ◽  
Flux Gradient

Abstract In this study, the authors have performed the variational computations for surface sensible heat fluxes over a large northern lake using observed wind, temperature gradient, and moisture gradient. In contrast with the conventional (Monin–Obukhov similarity theory) MOST-based flux-gradient method, the variational approach sufficiently utilizes observational meteorological conditions over the lake, where the conventional flux-gradient method performs poorly. Verifications using direct eddy-correlation measurements over Great Slave Lake, the fifth largest lake in North America in terms of surface area, during the open water period of 1999 demonstrate that the variational method yields good agreements between the computed and the measured sensible heat fluxes. It is also demonstrated that the variational method is more accurate than the flux-gradient method in computations of sensible heat flux across the air–water interface.

scholarly journals DYNAMICS OF HEAT FLUXES BY BOWEN AND MATMNXFLX AND NOAH FLDAS PRODUCTS IN THE PANTANAL OF MATO GROSSO.

2019 ◽  
Vol 46 (3) ◽  
pp. 07
Author(s):  
Leilane Gomes Duarte ◽  
Kelly Souza Romera ◽  
Marlus Sabino ◽  
Leone Francisco Amorim Curado ◽  
Rafael Da Silva Palácios ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Absolute Error ◽  
Soil Heat Flux ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Seasonal Behavior ◽  
Mato Grosso

This paper aimed to analyze the dynamics of the energy budget components: latent heat flux (LE), sensible heat flux (H) and soil heat flux (G), in the Mato Grosso Pantanal. The estimates of LE, H, and G were obtained by the Bowen ratio methods, using data from the micrometeorological tower located in the Baía das Pedras Park of SESC-Pantanal Ecological Resort, for the years 2011 to 2013. The normality of the variables Rn, LE, H and G, were tested by Kolmogorov-Smirnov test at 5% significance, and the seasonal differences of the fluxes were verified by the KruskalWallis test, α = 0.05. LE and H data from the remote sensing products MATMNXFLX and FLDAS_NOAH of the MERRA model was also acquired, and their comparison with the tower data was performed by the statistics of Spearman correlation (r), Mean Absolute Error (MAE), Root Mean Squared Erro (RMSE), bias, and Willmott's Concordance Index (d). It was observed that most of the available energy is used for evapotranspiration (latent heat), followed by sensible heat and soil heat flux. In the rainy season there is an increase in the partition of LE and G and reduction of H. Only the estimates of LE of MATMNXFLX and FLDAS_NOAH products correlate with the data observed in the meteorological tower. It is concluded that the energy partitions have a seasonal behavior and that the MATMNXFLX and FLDAS_NOAH products, after being calibrated, can be used to estimate LE in the Mato Grosso Pantanal.

scholarly journals ESTUDO DO CALOR SENSÍVEL E LATENTE OBTIDOS POR INTERMÉDIO DA RAZÃO DE BOWEN EM UMA CULTURA DE SOJA IRRIGADA.

Irriga ◽  
2007 ◽  
Vol 12 (3) ◽  
pp. 281-296 ◽  
Author(s):  
Edemo João Fernandes
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Vertical Displacement ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Soybean Crop ◽  
The Mean ◽  
Soil Water Conditions

ESTUDO DO CALOR SENSÍVEL E LATENTE OBTIDOS POR INTERMÉDIO DA RAZÃO DE BOWEN EM UMA CULTURA DE SOJA IRRIGADA.  Edemo João FernandesDepartamento de Engenharia Rural, Universidade Estadual Paulista, Campus de Jaboticabal, SP,[email protected]  1 RESUMO O experimento teve por objetivo estudar as variações dos fluxos de calor sensível e latente sobre uma cultura de soja irrigada, obtidos com a utilização da razão de Bowen. Foi construída uma estação micrometeorológica, com deslocamento vertical dos sensores para manter o mesmo nível de medidas acima da cobertura vegetal. A estação foi instalada na parte central da parcela, distante130 mda margem principal da direção dos ventos predominantes. Os fluxos foram calculados em função dos gradientes verticais de temperaturas determinadas a 0,15 e1,15 mde altura acima da cultura de soja. Em condições de bom suprimento de água e com a cultura cobrindo totalmente o solo o fluxo de calor latente é o maior consumidor da energia disponível na vegetação. O fluxo de calor sensível foi maior no início do desenvolvimento da cultura, quando o índice de área foliar foi menor. A cobertura vegetal é preponderante no consumo da energia disponível na vegetação em forma de calor latente. UNITERMOS: fluxos de calor, radiação líquida, temperatura do ar.  FERNANDES, E. J. F. STUDY OF SENSIBLE AND LATENT HEAT OBTAINED BY BOWEN RATIO FROM IRRIGATED SOYBEAN CROP  2 ABSTRACT                                       The goal of this experiment was to study the latent and sensible heat variation determined by Bowen ratio from an irrigated soybean crop. A micrometeorological station with vertical displacement was constructed to maintain the same level of all measures over the canopy. The station was installed in the center of the crop, and it was over130 maway from the main edge of the predominant wind direction. Fluxes were calculated by vertical temperature gradient determined at 0.15 and1.15 mover the canopy. The latent heat flux was the mean energy consumer when the canopy covered the soil totally, and there were good soil water conditions. The sensible heat flux was greater when the soil was not totally covered by the canopy. The canopy was essential on the amount of latent heat dissipated by the crop. KEYWORDS: heat fluxes, net radiation, air temperature.

scholarly journals An Application of the Variational Method to Computation of Sensible Heat Flux over a Deciduous Forest

2005 ◽  
Vol 44 (1) ◽  
pp. 144-152 ◽  
Author(s):  
Zuohao Cao ◽  
Jianmin Ma
Keyword(s):  
Heat Flux ◽  
Variational Method ◽  
Forest Canopy ◽  
Deciduous Forest ◽  
Sensible Heat Flux ◽  
Meteorological Conditions ◽  
Heat Fluxes ◽  
Eddy Correlation ◽  
Sensible Heat ◽  
Variance Method

Abstract A variational method is employed to compute surface sensible heat fluxes over a deciduous forest using observed temperature, temperature variance, and wind. Because the variational approach is able to take into account comprehensive observational meteorological conditions over a heterogeneous surface, it is applicable to the computations of sensible heat flux over a forest canopy in which the conventional flux-variance method is difficult to use. Verifications using the direct eddy-correlation measurements over a deciduous forest during the fully leafed summer of 1988 and the leafless winter of 1990 show that the variational method yields very good agreements between the computed and the measured sensible heat fluxes. It is also shown that the variational method is much more accurate than the flux-variance method in computations of sensible heat flux over a forest canopy.

scholarly journals Scintillometer-Based Estimates of Sensible Heat Flux Using Lidar-Derived Surface Roughness

2012 ◽  
Vol 13 (4) ◽  
pp. 1317-1331 ◽  
Author(s):  
Hatim M. E. Geli ◽  
Christopher M. U. Neale ◽  
Doyle Watts ◽  
John Osterberg ◽  
Henk A. R. De Bruin ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Roughness ◽  
Weighting Function ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Climatic Conditions ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Topographic Map ◽  
Vegetation Height

Abstract The estimation of sensible heat flux, H, using large aperture scintillometer (LAS) under varying surface heterogeneity conditions was investigated. Surface roughness features characterized by variable topography and vegetation height were represented using data derived from the highly accurate light detection and range (lidar) techniques as well as from traditional vegetation survey and topographic map methods. The study was conducted at the Cibola National Wildlife Refuge, Southern California, over a riparian zone covered with natural vegetation dominated by tamarisk trees interspersed with bare soil in a region characterized by arid to semiarid climatic conditions. Estimates of H were obtained using different representations of surface roughness features derived from both traditional and lidar methods to estimate LAS beam height [z(u)] at each increment u along its path, vegetation height (hc), displacement height (d), and roughness length (z0) combined with the LAS weighing function, W(u), along the path. The effect of the LAS 3D footprint was examined to account for the contribution from the individual patches in the upwind direction, hence on the estimates of H. The results showed better agreement between LAS and Bowen ratio sensible heat fluxes when lidar-derived surface roughness was used, especially when considering the LAS 3D footprint effects. It was also found that, under certain conditions, the LAS path weighted hc and d obtained using the LAS weighting function W(u) is a good approximation of the 3D weighted footprint values.

scholarly journals Bowen ratio determination of sensible and latent heat fluxes in a humid tropical environment at Ile- Ife, Nigeria

MAUSAM ◽  
2022 ◽  
Vol 52 (4) ◽  
pp. 669-678
Author(s):  
O. O. JEGEDE ◽  
Th. FOKEN ◽  
A. A. BALOGUN ◽  
O. J. ABIMBOLA
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Bowen Ratio ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Night Time ◽  
Forest Zone ◽  
Surface Conditions

The Bowen ratio energy balance (BREB) method is the most widely used for estimating the fluxes of sensible heat and latent heat near the surface largely because of its conceptual simplicity and the robustness of instrumentation required. We have adopted the same technique here to study partitioning of measured available energy (difference of net radiation and soil heat flux) over bare soil at a humid tropical location in Ile-Ife, Nigeria (7° 33' N, 4° 34' E) between 7 and 10 March, 1999. Results obtained of the diurnal variations of the both fluxes in relation to the changing surface conditions (case studies) are quite satisfactory. For dry days, the sensible heat flux is comparatively of the same magnitude as the latent heat flux but it is less, about 10-60% for the wet surface conditions. It is clear from the present study that for the tropical forest zone, evaporation is the next important factor after radiation in the energy balance due to the humid conditions that usually prevail. Except for the few instances when very weak gradients exist, particularly of moisture, during transition periods (at sunrise or sunset), the technique has worked satisfactorily for day as well as night time periods regardless of prevailing weather conditions.

scholarly journals Lidar Measurement of Boundary Layer Evolution to Determine Sensible Heat Fluxes

2005 ◽  
Vol 6 (6) ◽  
pp. 840-853 ◽  
Author(s):  
W. E. Eichinger ◽  
H. E. Holder ◽  
R. Knight ◽  
J. Nichols ◽  
D. I. Cooper ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Potential Temperature ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Eddy Correlation ◽  
High Time Resolution ◽  
Lidar Measurement ◽  
Sensible Heat ◽  
Creek Watershed

Abstract The Soil Moisture–Atmosphere Coupling Experiment (SMACEX) was conducted in the Walnut Creek watershed near Ames, Iowa, over the period from 15 June to 11 July 2002. A main focus of SMACEX is the investigation of the interactions between the atmospheric boundary layer, surface moisture, and canopy. A vertically staring elastic lidar was used to provide a high-time-resolution continuous record of the boundary layer height at the edge between a soybean and cornfield. The height and thickness of the entrainment zone are used to estimate the surface sensible heat flux using the Batchvarova–Gryning boundary layer model. Flux estimates made over 6 days are compared to conventional eddy correlation measurements. The calculated values of the sensible heat flux were found to be well correlated (R2 = 0.79, with a slope of 0.95) when compared to eddy correlation measurements in the area. The standard error of the flux estimates was 21.4 W m−2 (31% rms difference between this method and surface measurements), which is somewhat higher than a predicted uncertainty of 16%. The major sources of error were from the estimates of the vertical potential temperature gradient and an assumption that the entrainment parameter A was equal to the ratio of the entrainment flux and the surface heat flux.

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