Turbulent sensible heat flux in Łódź, Central Poland, obtained from scintillometer and eddy covariance measurements

2013 ◽  
Vol 22 (5) ◽  
pp. 603-613 ◽  
Author(s):  
Mariusz Zieliński ◽  
Krzysztof Fortuniak ◽  
Włodzimierz Pawlak ◽  
Mariusz Siedlecki
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Central Poland ◽  
Eddy Covariance Measurements

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

2013 ◽  
Vol 13 (9) ◽  
pp. 4645-4666 ◽  
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.

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

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 299
Author(s):  
Noman Ali Buttar ◽  
Hu Yongguang ◽  
Josef Tanny ◽  
M Waqar Akram ◽  
Abdul Shabbir
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Latent Heat ◽  
Sensible Heat Flux ◽  
Soil Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Effect Of Temperature ◽  
Sensible Heat ◽  
Fine Wire

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.

scholarly journals Four-year (2006–2009) eddy covariance measurements of CO<sub>2</sub> flux over an urban area in Beijing

2012 ◽  
Vol 12 (17) ◽  
pp. 7881-7892 ◽  
Author(s):  
H. Z. Liu ◽  
J. W. Feng ◽  
L. Järvi ◽  
T. Vesala
Keyword(s):  
Heat Flux ◽  
Urban Area ◽  
Eddy Covariance ◽  
Sensible Heat Flux ◽  
Source Area ◽  
Carbon Dioxide Flux ◽  
Heat Fluxes ◽  
Urban Surface ◽  
Sensible Heat ◽  
Main Component

Abstract. Long-term measurements of carbon dioxide flux (Fc) and the latent and sensible heat fluxes were performed using the eddy covariance (EC) method in Beijing, China over a 4-yr period in 2006–2009. The EC setup was installed at a height of 47 m on the Beijing 325-m meteorological tower in the northwest part of the city. Latent heat flux dominated the energy exchange between the urban surface and the atmosphere in summer, while sensible heat flux was the main component in the spring. Winter and autumn were two transition periods of the turbulent fluxes. The source area of Fc was highly heterogeneous, which consisted of buildings, parks, and highways. It was of interest to study of the temporal and spatial variability of Fc in this urban environment of a developing country. Both on diurnal and monthly scale, the urban surface acted as a net source for CO2 and downward fluxes were only occasionally observed. The diurnal pattern of Fc showed dependence on traffic and the typical two peak traffic patterns appeared in the diurnal cycle. Also Fc was higher on weekdays than on weekends due to the higher traffic volumes on weekdays. On seasonal scale, Fc was generally higher in winter than during other seasons likely due to domestic heating during colder months. Total annual average CO2 emissions from the neighborhood of the tower were estimated to be 4.90 kg C m−2 yr−1 over the 4-yr period. Total vehicle population was the most important factor controlling the inter-annual variability of Fc in this urban area.

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%).

Progress in Preliminary Processing of Eddy Covariance Flux Data

2013 ◽  
Vol 807-809 ◽  
pp. 1909-1914
Author(s):  
Xin Ying Tang ◽  
Lin Han ◽  
Ge Wang
Keyword(s):  
Heat Flux ◽  
Eddy Covariance ◽  
Sensible Heat Flux ◽  
Observation Data ◽  
Sensible Heat ◽  
Data Quality Control ◽  
Flux Data ◽  
Preliminary Processing ◽  
Processing Software ◽  
The Difference

The eddy covariance (EC) technique of observation is a standard method for direct measurement of CO2, H2O and energy flux between vegetation and the atmosphere, the calculation formula of which is based on a series of assumptions. In reality, the assumed conditions are usually not satisfied, and the flux data is subject to significant deviation, thus the measured result should be corrected. The difference in data processing may lead to obvious difference in the calculated results of sensible heat flux and latent heat flux, while the universality of existing flux processing software is not verified. On the basis of domestic and foreign literature, this paper systematically summarizes and evaluates the preliminary processing of EC observation data in the aspects of principle and method of flux observation, rejection and interpolation of flux data, quality control and evaluation of flux data.

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