Fetch Effect on Flux-Variance Estimations of Sensible and Latent Heat Fluxes of Camellia Sinensis

Precise estimation of surface-atmosphere exchange is a major challenge in micrometeorology. Previous literature presented the eddy covariance (EC) as the most reliable method for the measurements of such fluxes. Nevertheless, the EC technique is quite expensive and complex, hence other simpler methods are sought. One of these methods is Flux-Variance (FV). The FV method estimates sensible heat flux (H) using high frequency (~10Hz) air temperature measurements by a fine wire thermocouple. Additional measurements of net radiation (Rn) and soil heat flux (G) allow the derivation of latent heat flux (LE) as the residual of the energy balance equation. In this study, the Flux Variance method was investigated, and the results were compared against eddy covariance measurements. The specific goal of the present study was to assess the performance of the FV method for the estimation of surface fluxes along a variable fetch. Experiment was carried out in a tea garden; an EC system measured latent and sensible heat fluxes and five fine-wire thermocouples were installed towards the wind dominant direction at different distances (fetch) of TC1 = 170 m, TC2 = 165 m, TC3 = 160 m, TC4 = 155 m and TC5 = 150 m from the field edge. Footprint analysis was employed to examine the effect of temperature measurement position on the ratio between 90% footprint and measurement height. Results showed a good agreement between FV and EC measurements of sensible heat flux, with all regression coefficients (R2) larger than 0.6; the sensor at 170 m (TC1), nearest to the EC system, had highest R2 = 0.86 and lowest root mean square error (RMSE = 25 Wm−2). The estimation of LE at TC1 was also in best agreement with eddy covariance, with the highest R2 = 0.90. The FV similarity constant varied along the fetch within the range 2.2–2.4.

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Observed Impact of Atmospheric Aerosols on the Surface Energy Budget

Earth Interactions ◽

10.1175/2013ei000523.1 ◽

2013 ◽

Vol 17 (14) ◽

pp. 1-22 ◽

Cited By ~ 27

Author(s):

Allison L. Steiner ◽

Dori Mermelstein ◽

Susan J. Cheng ◽

Tracy E. Twine ◽

Andrew Oliphant

Keyword(s):

Heat Flux ◽

Surface Energy ◽

Latent Heat ◽

Atmospheric Aerosols ◽

Sensible Heat Flux ◽

Surface Fluxes ◽

Heat Fluxes ◽

Surface Energy Budget ◽

Environmental Drivers ◽

Sensible Heat

Abstract Atmospheric aerosols scatter and potentially absorb incoming solar radiation, thereby reducing the total amount of radiation reaching the surface and increasing the fraction that is diffuse. The partitioning of incoming energy at the surface into sensible heat flux and latent heat flux is postulated to change with increasing aerosol concentrations, as an increase in diffuse light can reach greater portions of vegetated canopies. This can increase photosynthesis and transpiration rates in the lower canopy and potentially decrease the ratio of sensible to latent heat for the entire canopy. Here, half-hourly and hourly surface fluxes from six Flux Network (FLUXNET) sites in the coterminous United States are evaluated over the past decade (2000–08) in conjunction with satellite-derived aerosol optical depth (AOD) to determine if atmospheric aerosols systematically influence sensible and latent heat fluxes. Satellite-derived AOD is used to classify days as high or low AOD and establish the relationship between aerosol concentrations and the surface energy fluxes. High AOD reduces midday net radiation by 6%–65% coupled with a 9%–30% decrease in sensible and latent heat fluxes, although not all sites exhibit statistically significant changes. The partitioning between sensible and latent heat varies between ecosystems, with two sites showing a greater decrease in latent heat than sensible heat (Duke Forest and Walker Branch), two sites showing equivalent reductions (Harvard Forest and Bondville), and one site showing a greater decrease in sensible heat than latent heat (Morgan–Monroe). These results suggest that aerosols trigger an ecosystem-dependent response to surface flux partitioning, yet the environmental drivers for this response require further exploration.

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Estimation of the Latent Heat Flux over Irrigated Short Fescue Grass for Different Fetches

Atmosphere ◽

10.3390/atmos12030322 ◽

2021 ◽

Vol 12 (3) ◽

pp. 322

Author(s):

Francesc Castellví ◽

Pedro Gavilán

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Sensible Heat Flux ◽

Surface Fluxes ◽

Heat Fluxes ◽

The Other ◽

Sensible Heat ◽

Surface Renewal ◽

Residual Method ◽

Flux Footprints

Often in agrometeorology the instrumentation required to estimate turbulent surface fluxes must be installed at sites where fetch is not sufficient for a sector of wind directions. For different integrated flux-footprints (IFFP) thresholds and taking as a reference the half-hourly latent heat fluxes (LE) measured with a large weighing lysimeter (LELys), the eddy covariance (EC) method and two methods based on surface renewal (SR) analysis to estimate LE were tested over short fescue grass. One method combined SR with the flux-gradient (profile) relationship, SR-P method, and the other with the dissipation method, SR-D method. When LE was estimated using traces of air moisture, good performances were obtained using the EC and the SR-P methods for samples with IFFP higher than 85%. However, the closest LE estimates were obtained using the residual method. For IFFP higher than 50%, the residual method combined with the sensible heat flux estimates determined using the SR-P method performed close to LELys and using the SR-D method good estimates were obtained for accumulated LELys. To estimate the sensible heat flux, the SR-D method can be recommended for day-to-day use by farmers because it is friendly and affordable.

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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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Comparing Aircraft-Based Remotely Sensed Energy Balance Fluxes with Eddy Covariance Tower Data Using Heat Flux Source Area Functions

Journal of Hydrometeorology ◽

10.1175/jhm467.1 ◽

2005 ◽

Vol 6 (6) ◽

pp. 923-940 ◽

Cited By ~ 63

Author(s):

JoséL. Chávez ◽

Christopher M. U. Neale ◽

Lawrence E. Hipps ◽

John H. Prueger ◽

William P. Kustas

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Eddy Covariance ◽

Latent Heat ◽

Latent Heat Flux ◽

Sensible Heat Flux ◽

Source Area ◽

Soil Heat Flux ◽

Sensible Heat ◽

Atmospheric Conditions

Abstract In an effort to better evaluate distributed airborne remotely sensed sensible and latent heat flux estimates, two heat flux source area (footprint) models were applied to the imagery, and their pixel weighting/integrating functionality was investigated through statistical analysis. Soil heat flux and sensible heat flux models were calibrated. The latent heat flux was determined as a residual from the energy balance equation. The resulting raster images were integrated using the 2D footprints and were compared to eddy covariance energy balance flux measurements. The results show latent heat flux estimates (adjusted for closure) with errors of (mean ± std dev) −9.2 ± 39.4 W m−2, sensible heat flux estimate errors of 9.4 ± 28.3 W m−2, net radiation error of −4.8 ± 20.7 W m−2, and soil heat flux error of −0.5 ± 24.5 W m−2. This good agreement with measured values indicates that the adopted methodology for estimating the energy balance components, using high-resolution airborne multispectral imagery, is appropriate for modeling latent heat fluxes. The method worked well for the unstable atmospheric conditions of the study. The footprint weighting/integration models tested indicate that they perform better than simple pixel averages upwind from the flux stations. In particular the flux source area model (footprint) seemed to better integrate the resulting heat flux image pixels. It is suggested that future studies test the methodology for heterogeneous surfaces under stable atmospheric conditions.

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Influence of a New Turbulence Regime on the Global Air–Sea Heat Fluxes

Journal of Climate ◽

10.1175/2008jcli2279.1 ◽

2008 ◽

Vol 21 (22) ◽

pp. 5925-5941 ◽

Cited By ~ 7

Author(s):

Erik Sahlée ◽

Ann-Sofi Smedman ◽

Anna Rutgersson ◽

Ulf Högström

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Latent Heat Flux ◽

Sensible Heat Flux ◽

Sensitivity Study ◽

Surface Fluxes ◽

Heat Fluxes ◽

Turbulence Structure ◽

Sensible Heat ◽

Monsoon Period

Abstract Recent research has found that boundary layer turbulence changes its organization as the stratification approaches neutral from the unstable side. When the thermal forcing weakens in combination with wind speed above approximately 10 m s−1, detached eddies are formed in the upper part of the surface layer. These eddies effectively transport drier and colder air from aloft to the surface as they move downward, thereby enhancing the surface fluxes of sensible and latent heat. This effect has been observed over both land and sea; that is, it is not dependent on the nature of the underlying surface. Here the authors perform a sensitivity study of how this reorganization of the turbulence structure influences the global air–sea heat fluxes. Using modified bulk formulations incorporating this effect, the magnitude of the enhancement in a climatic sense was estimated by the use of 40-yr ECMWF Re-Analysis (ERA-40) data in the bulk formulas. It is found that for the 1979–2001 period, the global increase of the latent and sensible heat fluxes over the ice-free oceans is 3.6 and 1.2 W m−2, respectively. These numbers suggest that this effect is of some significance. The results also indicate that the regional and seasonal variability may be large. The largest annual increases are found over the southern oceans between 30° and 60°S where the sensible heat flux increases by 2.3 W m−2 and the latent heat flux by 6.5 W m−2. Ocean areas close to the equator experience almost no increase, whereas the latent heat flux from the Arabian Sea during the monsoon period is enhanced by 11.5 W m−2.

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Comparison of turbulent structures and energy fluxes over exposed and debris-covered glacier ice

Journal of Glaciology ◽

10.1017/jog.2020.23 ◽

2020 ◽

Vol 66 (258) ◽

pp. 543-555 ◽

Cited By ~ 2

Author(s):

Lindsey Nicholson ◽

Ivana Stiperski

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Similarity Theory ◽

Sensible Heat Flux ◽

Heat Fluxes ◽

Temperature Fields ◽

Sensible Heat ◽

Energy Fluxes ◽

Glacier Surface ◽

Debris Cover

AbstractWe present the first direct comparison of turbulence conditions measured simultaneously over exposed ice and a 0.08 m thick supraglacial debris cover on Suldenferner, a small glacier in the Italian Alps. Surface roughness, sensible heat fluxes (~20–50 W m−2), latent heat fluxes (~2–10 W m−2), topology and scale of turbulence are similar over both glacier surface types during katabatic and synoptically disturbed conditions. Exceptions are sunny days when buoyant convection becomes significant over debris-covered ice (sensible heat flux ~ −100 W m−2; latent heat flux ~ −30 W m−2) and prevailing katabatic conditions are rapidly broken down even over this thin debris cover. The similarity in turbulent properties implies that both surface types can be treated the same in terms of boundary layer similarity theory. The differences in turbulence between the two surface types on this glacier are dominated by the radiative and thermal contrasts, thus during sunny days debris cover alters both the local surface turbulent energy fluxes and the glacier component of valley circulation. These variations under different flow conditions should be accounted for when distributing temperature fields for modeling applications over partially debris-covered glaciers.

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Comparison of energy fluxes from eddy covariance and scintillometer over an agricultural field

10.5194/egusphere-egu2020-10168 ◽

2020 ◽

Author(s):

Matěj Orság ◽

Milan Fischer ◽

Josef Eitzinger ◽

Miroslav Trnka

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Eddy Covariance ◽

Latent Heat ◽

Soil Heat Flux ◽

Radiation Balance ◽

Energy Balance Closure ◽

Sensible Heat ◽

Agricultural Field ◽

Available Energy

In this study we compare turbulent energy fluxes obtained from eddy covariance (EC) (LI-7500A, LI-COR + Windmaster, Gill Instruments) and large aperture scintillometer (BLS900, Scintec) over an agricultural field (wheat field, straw and bare soil). As the EC method provides direct measurements of sensible heat (HEC) and latent heat (LEEC) fluxes we use it as a reference method. The EC method enables to determine fluxes within a footprint centered around the point of measurement in the middle of the field. The scintillometer provides an estimation of sensible heat flux (HSC), derived from air refractive index fluctuation integrated over the measurement path length, in this case 570 m diagonally across whole field. The reference measurements of the radiation balance components consist of 4-component net radiometer for net radiation (Rn) (NR01, Hukseflux), three soil heat flux plates for soil heat flux (G) monitoring (HFP01, Hukseflux), including thermocouples for quantification of the heat storage above the soil heat flux plates. The scintillometer-based latent heat (LESC) is calculated as a residuum from available energy (Rn-G) and HSC, provided by scintillometer. The measurement of radiation balance components was located at the top of 3.5 m mast with the EC system, while the soil heat flux plates were collocated around in 5 cm depth. The site is a flat, rectangular agricultural field (app. 16.5 ha), in the north-eastern Austria, Danube river lowland (48.21N, 16.622E), sown with winter wheat during growing season 2019. The measurement campaign was established in February 2019 with aim for multi-seasonal monitoring. The EC measurement height is 2.7 m, the scintillometer transmitter and receiver are fixed on 4 m masts, facing towards each other from NW and SE corners of the field.Comparison of the EC-based turbulent fluxes (HEC+LEEC) and the available energy (Rn-G) during the period March to Mid-June showed a very good agreement, resulting in the energy balance closure of 0.96 (R2 = 0.93). This suggest high accuracy and robustness of the measurement setup together with the ability of the EC method to capture all scales of eddies responsible for energy transport at this site. The comparison of methods indicates that HSC overestimated HEC by 10 % (R2 = 0.74) and LESC underestimated LEEC by 13 % (R2 = 0.81). Related to Rn, the HEC, LEEC and G fluxes accounted for 22 % (R2 = 0.53), 59 % (R2 = 0.70) and 15% (R2 = 0.62) of the Rn flux, respectively. We assume that the combination of EC and scintillometer method has a potential to bring deeper insight into the analysis of the energy balance closure problem.

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Multi-season eddy covariance observations of energy, water and carbon fluxes over a suburban area in Swindon, UK

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-4645-2013 ◽

2013 ◽

Vol 13 (9) ◽

pp. 4645-4666 ◽

Cited By ~ 56

Author(s):

H. C. Ward ◽

J. G. Evans ◽

C. S. B. Grimmond

Keyword(s):

Heat Flux ◽

Eddy Covariance ◽

Latent Heat ◽

Sensible Heat Flux ◽

Significant Proportion ◽

Suburban Area ◽

Anthropogenic Heat ◽

Surface Conductance ◽

Sensible Heat ◽

Anthropogenic Heat Flux

Abstract. Eddy covariance measurements of the turbulent sensible heat, latent heat and carbon dioxide fluxes for 12 months (2011–2012) are reported for the first time for a suburban area in the UK. The results from Swindon are comparable to suburban studies of similar surface cover elsewhere but reveal large seasonal variability. Energy partitioning favours turbulent sensible heat during summer (midday Bowen ratio 1.4–1.6) and latent heat in winter (0.05–0.7). A significant proportion of energy is stored (and released) by the urban fabric and the estimated anthropogenic heat flux is small but non-negligible (0.5–0.9 MJ m−2 day−1). The sensible heat flux is negative at night and for much of winter daytimes, reflecting the suburban nature of the site (44% vegetation) and relatively low built fraction (16%). Latent heat fluxes appear to be water limited during a dry spring in both 2011 and 2012, when the response of the surface to moisture availability can be seen on a daily timescale. Energy and other factors are more relevant controls at other times; at night the wind speed is important. On average, surface conductance follows a smooth, asymmetrical diurnal course peaking at around 6–9 mm s−1, but values are larger and highly variable in wet conditions. The combination of natural (vegetative) and anthropogenic (emission) processes is most evident in the temporal variation of the carbon flux: significant photosynthetic uptake is seen during summer, whilst traffic and building emissions explain peak release in winter (9.5 g C m−2 day−1). The area is a net source of CO2 annually. Analysis by wind direction highlights the role of urban vegetation in promoting evapotranspiration and offsetting CO2 emissions, especially when contrasted against peak traffic emissions from sectors with more roads. Given the extent of suburban land use, these results have important implications for understanding urban energy, water and carbon dynamics.

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Energy balance in a renewal sugarcane area with fallow period and soybean cultivation

Ciência e Natura ◽

10.5902/2179460x53222 ◽

2020 ◽

Vol 42 ◽

pp. e39

Author(s):

Rubmara Ketzer Oliveira ◽

Luciano Sobral Fraga Junior ◽

Larissa Brêtas Moura ◽

Debora Regina Roberti ◽

Felipe Gustavo Pilau

Keyword(s):

Heat Flux ◽

Energy Balance ◽

Latent Heat ◽

Latent Heat Flux ◽

Sensible Heat Flux ◽

Heat Fluxes ◽

Rainfall Regime ◽

Sensible Heat ◽

Energy Fluxes ◽

Fallow Period

Brazil is the main sugarcane producer in the world, which is intended for various purposes, from food to power generation. Soybean cultivation in areas of sugarcane under renewal has been growing progressively in Brazil. Quantifying energy fluxes at different stages of this process is essential for better management. The work was carried out in Piracicaba city, with the objective of analyzing the behavior of energy fluxes and the closing of the energy balance in a sugarcane renewal area with a fallow period followed by soybean cultivation. The latent and sensitive heat fluxes were obtained with the “Eddy covariance” method. The closing of the energy balance in the fallow period with straw-covered uncovered and soybean-cultivated soil presented a correlation coefficient of 0.88, 0.78 and 0.71, respectively. In the period without cultivation, the sensible heat flux was predominant in relation to the latent heat flux, varying according to the rainfall regime. The presence of straw under the soil in the fallow period affected the latent heat flux. With soybean cultivation, the latent heat flux surpassed the sensible heat flux.

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Study on the Land-Atmosphere Interaction in the Coordination Effect of Westerly Wind and Monsoon

10.5194/egusphere-egu21-2318 ◽

2021 ◽

Author(s):

Maoshan Li ◽

Lingzhi Wang ◽

Wei Fu ◽

Ming Gong ◽

Na Chang

Keyword(s):

Heat Flux ◽

Latent Heat ◽

Wind Direction ◽

Wind Field ◽

Sensible Heat Flux ◽

Heat Fluxes ◽

Specific Humidity ◽

Sensible Heat ◽

Mount Everest ◽

Convective Boundary

&#160;Different underlying surfaces have differing diversities, complex compositions and uneven distributions and contribute to diverse and complex land surfaces. As the main input factor for atmospheric energy, the surface greatly affects the various interactions between the ground and the atmosphere and even plays a key role in local areas on the Tibetan Plateau. The characteristics of the atmospheric boundary layer structure of the plateau and the land-atmosphere interaction under the control of different wind fields in the south branch of the westerly wind and the plateau monsoon are discussed. Results show that the height of the atmospheric boundary layer at each station under the westerly south branch wind field is higher than that under the summer monsoon wind field. The height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River in the southwest wind field are 3250 m, 2250 m, 2760 m and 3500 m. while the height of the convective boundary layers of Mount Everest, Nyingchi, Nagqu and Shiquan River under the plateau monsoon field are 2000 m, 2100 m, 1650 m and 2000 m. The specific humidity of the surface layer at all site is larger on July than it on other months. The specific humidity of the surface layer in Linzhi area is larger than that of the other three regions, and it reaches 12.88 g&#183;kg-1 at the maximum. The wind direction on Mount Everest over 1200 m is dominated by westerly winds in May and October. The wind direction on Nyingchi above 1500 m is dominated by westerly winds in May and October, and in July, winds above 1200 m is dominated by southerly winds. The wind direction of Shiquan River in May and October is dominated by west-southwest wind, and the wind direction of Shiquan River in July is dominated by west-northwest wind. Secondly, variation characteristics of surface fluxes were analyzed by using the eddy covariance observations from four stations of Pailong(entrance of Canyon), Danka (middle of Canyon), Kabu (end of Canyon) , and Motuo (end of Canyon) in the southeastern gorge area of Tibet. The changing trend of monthly averaged daily sensible heat flux at Kabu station is fluctuating. Sensible heat flux and latent heat flux at Motuo station have the same variation characteristics. Latent heat fluxes increase first and then decrease at all four stations. Seasonal variations of soil heat flux are obvious, characterizing positive values in spring and summer and negative values in autumn and winter. The diurnal variation intensity of net radiation flux is summer>spring>autumn>winter.&#160; &#160;Energy closure rates of Danka, Pailong, Motuo, and Kabu stations are 70.86%, 68.91%, 69.29%, and 67.23%, respectively. Latent heat fluxes and soil heat fluxes increase, and sensible heat fluxes decrease as increasing precipitation at the four stations. The sensible heat flux and soil heat flux respond synchronously to precipitation changes, and the changes in latent heat have a significant lag in response to precipitation changes.

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