A simple model for estimating the Bowen ratio from climatic factors for determining latent and sensible heat flux

Abstract. Twelve-years of eddy-covariance measurements conducted above a boreal Scots pine forest in Hyytiälä, Southern Finland, were analyzed to assess the seasonal and inter-annual variability of surface conductance (gs) and energy partitioning. The gs had distinct annual course, driven by the seasonal cycle of the Scots pine. Low gs (2–3 mm s−1 in April) restricted transpiration in springtime and caused the sensible heat flux to peak in May–June while evapotranspiration takes over later in July–August when gs is typically 5–7 mm s−1. Hence, during normal years Bowen ratio decreases from 4–6 in April to 0.7–0.9 in August. Sensitivity of gs to ambient vapor pressure deficit (D) was relatively constant but the reference value at D=1 kPa varied seasonally and between years. Only two drought episodes when volumetric soil moisture content in upper mineral soil decreased below 0.15 m3 m−3 occurred during the period. Below this threshold value transpiration was strongly reduced, which promoted sensible heat exchange increasing Bowen ratio to 3–4. Annual evapotranspiration varied between 218 and 361 mm and accounted between 50% and 90% of equilibrium evaporation. The forest floor contributed between 16 and 25% of the total evapotranspiration on annual scale. The fraction stayed similar over the observed range of environmental conditions including drought. The inter-annual variability of evapotranspiration could not be linked to any mean climate parameter while the summertime sensible heat flux and net radiation were well explained by global radiation. The energy balance closure varied annually between 0.66 and 0.95 and had a distinct seasonal cycle with worse closure in spring when large proportion of available energy is partitioned into sensible heat.

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

Atmospheric Measurement Techniques Discussions ◽

10.5194/amtd-2-1383-2009 ◽

2009 ◽

Vol 2 (3) ◽

pp. 1383-1417 ◽

Cited By ~ 1

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.

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Study of energy balance components at different growth stages of green gram grown in new alluvial zone of West Bengal

MAUSAM ◽

10.54302/mausam.v71i2.29 ◽

2021 ◽

Vol 71 (2) ◽

pp. 315-320

Author(s):

MONDAL SOUMEN ◽

BANERJEE SAON ◽

CHAKRABORTY SHAON ◽

SAHA SALIL ◽

MUKHERJEE ASIS

Keyword(s):

Heat Flux ◽

Energy Balance ◽

West Bengal ◽

Sensible Heat Flux ◽

Bowen Ratio ◽

Green Gram ◽

Growth Stages ◽

Sensible Heat ◽

Net Radiation ◽

Ground Heat Flux

An experiment was conducted in the experimental farm of Bidhan Chandra KrishiViswavidyalaya, Nadia, West Bengal to study the radiation pattern and its balance over green gram (Vignaradiata var. Samrat). The BREB method was used to determine the sensible heat flux and latent energy. The net radiation was measured through net radiometer and the ground heat flux was measured using Fourier's law. Both the diurnal and seasonal variation of net radiation were studied. Similarly, the energy balance components were studied regularly for different crop growth stages as well as on diurnal basis. It is observed that the net radiation varies from 6.32 Wm-2 to 606.43 Wm-2. The latent heat flux constitutes more than 50% of the net radiation for all growth stages as depicted by energy balance partitioning. The sensible heat flux is partitioned into 10% to 20% of total net radiation throughout the growth stages of green gram, which is the lowest in magnitude among all three energy fluxes. The relationship between Bowen ratio and Vapour pressure deficit (VPD), Bowen ratio and Canopy air temperature difference (CATD) was studied. It was found that Bowen ratio is negatively correlated with VPD but positively correlated with CATD. This study enables to monitor ET pattern through latent heat flux and microclimatic characteristics through sensible and ground heat flux.

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

Hydrology and Earth System Sciences ◽

10.5194/hess-22-819-2018 ◽

2018 ◽

Vol 22 (1) ◽

pp. 819-830 ◽

Cited By ~ 10

Author(s):

Bart Schilperoort ◽

Miriam Coenders-Gerrits ◽

Willem Luxemburg ◽

César Jiménez Rodríguez ◽

César Cisneros Vaca ◽

...

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Solar Radiation ◽

Sensible Heat Flux ◽

Bowen Ratio ◽

Temperature Sensing ◽

Sensible Heat ◽

Distributed Temperature Sensing ◽

Available Energy ◽

Air Column

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 ) 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, 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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Seasonal and inter-annual variability of energy exchange above a boreal Scots pine forest

Biogeosciences ◽

10.5194/bg-7-3921-2010 ◽

2010 ◽

Vol 7 (12) ◽

pp. 3921-3940 ◽

Cited By ~ 36

Author(s):

S. Launiainen

Keyword(s):

Heat Flux ◽

Scots Pine ◽

Seasonal Cycle ◽

Sensible Heat Flux ◽

Bowen Ratio ◽

Pine Forest ◽

Surface Conductance ◽

Sensible Heat ◽

Annual Variability ◽

Scots Pine Forest

Abstract. Twelve-years of eddy-covariance measurements conducted above a boreal Scots pine forest in Hyytiälä, Southern Finland, were analyzed to assess the seasonal and inter-annual variability of surface conductance (gs) and energy partitioning. The gs had distinct annual course, driven by the seasonal cycle of the Scots pine. Low gs (2–3 mm s−1 in April) cause the sensible heat flux to peak in May–June while evapotranspiration takes over later in July–August when gs is typically 5–7 mm s−1. Hence, during normal years Bowen ratio decreases from 4–6 in April to 0.7–0.9 in August. Sensitivity of gs to ambient vapor pressure deficit (D) was relatively constant but the reference value at D = 1 kPa varied seasonally and between years. Only two drought episodes when volumetric soil moisture content in upper mineral soil decreased below 0.15 m3 m−3 occurred during the period. Below this threshold value, transpiration was strongly reduced, which promoted sensible heat exchange increasing Bowen ratio to 3–4. Annual evapotranspiration varied between 218 and 361 mm and accounted between 50% and 90% of equilibrium evaporation. The forest floor contributed between 16 and 25% of the total evapotranspiration on annual scale. The fraction stayed similar over the observed range of environmental conditions including drought periods. The inter-annual variability of evapotranspiration could not be linked to any mean climate variable while the summertime sensible heat flux and net radiation were well explained by global radiation. The energy balance closure varied annually between 0.66 and 0.95 and had a distinct seasonal cycle with worse closure in spring when a large proportion of available energy is partitioned into sensible heat.

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

Raega - O Espaço Geográfico em Análise ◽

10.5380/raega.v46i3.66981 ◽

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.

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

Irriga ◽

10.15809/irriga.2007v12n3p281-296 ◽

2007 ◽

Vol 12 (3) ◽

pp. 281-296 ◽

Cited By ~ 1

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.

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

Atmospheric Measurement Techniques ◽

10.5194/amt-2-741-2009 ◽

2009 ◽

Vol 2 (2) ◽

pp. 741-753 ◽

Cited By ~ 27

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%).

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

Journal of Hydrometeorology ◽

10.1175/jhm-d-11-085.1 ◽

2012 ◽

Vol 13 (4) ◽

pp. 1317-1331 ◽

Cited By ~ 9

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.

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

MAUSAM ◽

10.54302/mausam.v52i4.1739 ◽

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.

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