scholarly journals Urban Energy Fluxes in Built-Up Downtown Areas and Variations across the Urban Area, for Use in Dispersion Models

2011 ◽  
Vol 50 (6) ◽  
pp. 1341-1353 ◽  
Author(s):  
Steven Hanna ◽  
Edson Marciotto ◽  
Rex Britter
Keyword(s):  
Heat Flux ◽  
Rural Areas ◽  
Sensible Heat Flux ◽  
Tall Buildings ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Dispersion Models ◽  
Energy Fluxes ◽  
Downtown Area ◽  
Ground Heat Flux

AbstractSurface energy fluxes, at averaging times from 10 min to 1 h, are needed as inputs to most state-of-the-art dispersion models. The sensible heat flux is a major priority, because it is combined with the momentum flux to estimate the stability, the wind profile, and the turbulence intensities. Because of recent concerns about dispersion in built-up downtown areas of large cities, there is a need to estimate sensible heat flux in the midst of tall buildings. In this paper, the authors work with some high-quality and relevant but arguably underutilized data. The results of analysis of urban heat flux components from 10 locations in suburban and built-up downtown areas in Oklahoma City, Oklahoma, during the Joint Urban 2003 (JU2003) field experiment are presented here. At street level in the downtown area, in the midst of tall skyscrapers, the ground heat flux and the sensible heat flux are relatively large and the latent heat flux is relatively small when compared with concurrent fluxes observed in the upwind suburban areas. In confirmation of measurements in other cities, the sensible heat flux in the downtown area is observed to be slightly positive (10–20 W m−2) at night, indicating nearly neutral or slightly unstable conditions. Also in agreement with observations in other cities is that the ground heat flux in the downtown area has a magnitude that is 3 or 4 times that in suburban or rural areas. These results should permit improved parameterizations of sensible heat fluxes in the urban downtown area with tall buildings.

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

2020 ◽  
Vol 66 (258) ◽  
pp. 543-555 ◽  
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.

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

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.

scholarly journals Urban signals in high-resolution weather and climate simulations: role of urban land-surface characterisation

2020 ◽  
Vol 142 (1-2) ◽  
pp. 701-728
Author(s):  
Denise Hertwig ◽  
Sue Grimmond ◽  
Margaret A. Hendry ◽  
Beth Saunders ◽  
Zhengda Wang ◽  
...  
Keyword(s):  
Heat Flux ◽  
Land Cover ◽  
Sensible Heat Flux ◽  
Urban Land ◽  
Heat Fluxes ◽  
Anthropogenic Heat ◽  
Urban Surface ◽  
City Centre ◽  
Sensible Heat ◽  
Climate Simulations

Abstract Two urban schemes within the Joint UK Land Environment Simulator (JULES) are evaluated offline against multi-year flux observations in the densely built-up city centre of London and in suburban Swindon (UK): (i) the 1-tile slab model, used in climate simulations; (ii) the 2-tile canopy model MORUSES (Met Office–Reading Urban Surface Exchange Scheme), used for numerical weather prediction over the UK. Offline, both models perform better at the suburban site, where differences between the urban schemes are less pronounced due to larger vegetation fractions. At both sites, the outgoing short- and longwave radiation is more accurately represented than the turbulent heat fluxes. The seasonal variations of model skill are large in London, where the sensible heat flux in autumn and winter is strongly under-predicted if the large city centre magnitudes of anthropogenic heat emissions are not represented. The delayed timing of the sensible heat flux in the 1-tile model in London results in large negative bias in the morning. The partitioning of the urban surface into canyon and roof in MORUSES improves this as the roof tile is modelled with a very low thermal inertia, but phase and amplitude of the grid box-averaged flux critically depend on accurate knowledge of the plan-area fractions of streets and buildings. Not representing non-urban land cover (e.g. vegetation, inland water) in London results in severely under-predicted latent heat fluxes. Control runs demonstrate that the skill of both models can be greatly improved by providing accurate land cover and morphology information and using representative anthropogenic heat emissions, which is essential if the model output is intended to inform integrated urban services.

The progress on the observation and modeling of surface heat fluxes and evapotranspiration over heterogeneous landscapes of the Third Pole region

2020 ◽  
Author(s):  
Yaoming Ma
Keyword(s):  
Heat Flux ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Sensible Heat Flux ◽  
Surface Heat ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Surface Heat Fluxes ◽  
The Third ◽  
Land Surface Heat Fluxes

<p>The exchange of heat and water vapor between land surface and atmosphere over the Third Pole region (Tibetan Plateau and nearby surrounding region) plays an important role in Asian monsoon, westerlies and the northern hemisphere weather and climate systems. Supported by various agencies in the People’s Republic of China, a Third Pole Environment (TPE) observation and research Platform (TPEORP) is now implementing over the Third Pole region. The background of the establishment of the TPEORP, the establishing and monitoring plan of long-term scale (5-10 years) of it will be shown firstly. Then the preliminary observational analysis results, such as the characteristics of land surface energy fluxes partitioning and the turbulent characteristics will also been shown in this study. Then, the parameterization methodology based on satellite data and the atmospheric boundary layer (ABL) observations has been proposed and tested for deriving regional distribution of net radiation flux, soil heat flux, sensible heat flux and latent heat flux (evapotranspiration (ET)) and their variation trends over the heterogeneous landscape of the Tibetan Plateau (TP) area. To validate the proposed methodology, the ground measured net radiation flux, soil heat flux, sensible heat flux and latent heat flux of the TPEORP are compared to the derived values. The results showed that the derived land surface heat fluxes over the study areas are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface feature. And the estimated land surface heat fluxes are in good agreement with ground measurements, and all the absolute percent difference in less than 10% in the validation sites. The sensible heat flux has increased slightly and the latent heat flux has decreased from 2001 to 2016 over the TP. It is therefore conclude that the proposed methodology is successful for the retrieval of land surface heat fluxes and ET over heterogeneous landscape of the TP area. Further improvement of the methodology and its applying field over the whole Third Pole region and Pan-Third Pole region were also discussed.</p>

scholarly journals A New Technique to Estimate Sensible Heat Fluxes around Micrometeorological Towers Using Small Unmanned Aircraft Systems

2017 ◽  
Vol 34 (9) ◽  
pp. 2103-2112 ◽  
Author(s):  
Temple R. Lee ◽  
Michael Buban ◽  
Edward Dumas ◽  
C. Bruce Baker
Keyword(s):  
Heat Flux ◽  
Land Surface ◽  
Spatial Scales ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Unmanned Aircraft ◽  
Unmanned Aircraft Systems ◽  
Sensible Heat ◽  
Aircraft Systems ◽  
Convection Initiation

AbstractUpscaling point measurements from micrometeorological towers is a challenging task that is important for a variety of applications, for example, in process studies of convection initiation, carbon and energy budget studies, and the improvement of model parameterizations. In the present study, a technique was developed to determine the horizontal variability in sensible heat flux H surrounding micrometeorological towers. The technique was evaluated using 15-min flux observations, as well as measurements of land surface temperature and air temperature obtained from small unmanned aircraft systems (sUAS) conducted during a one-day measurement campaign. The computed H was found to be comparable to the micrometeorological measurements to within 5–10 W m−2. Furthermore, when comparing H computed using this technique with H determined using large-eddy simulations (LES), differences of <10 W m−2 were typically found. Thus, implementing this technique using observations from sUAS will help determine sensible heat flux variability at horizontal spatial scales larger than can be provided from flux tower measurements alone.

Observed Impact of Atmospheric Aerosols on the Surface Energy Budget

2013 ◽  
Vol 17 (14) ◽  
pp. 1-22 ◽  
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.

scholarly journals Evaluation of a Two-Source Snow–Vegetation Energy Balance Model for Estimating Surface Energy Fluxes in a Rangeland Ecosystem

2014 ◽  
Vol 15 (1) ◽  
pp. 143-158 ◽  
Author(s):  
Cezar Kongoli ◽  
William P. Kustas ◽  
Martha C. Anderson ◽  
John M. Norman ◽  
Joseph G. Alfieri ◽  
...  
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Surface Energy ◽  
Snow Cover ◽  
Sensible Heat Flux ◽  
Energy Balance Model ◽  
Balance Model ◽  
Sensible Heat ◽  
Energy Fluxes ◽  
Surface Energy Fluxes

Abstract The utility of a snow–vegetation energy balance model for estimating surface energy fluxes is evaluated with field measurements at two sites in a rangeland ecosystem in southwestern Idaho during the winter of 2007: one site dominated by aspen vegetation and the other by sagebrush. Model parameterizations are adopted from the two-source energy balance (TSEB) modeling scheme, which estimates fluxes from the vegetation and surface substrate separately using remotely sensed measurements of land surface temperature. Modifications include development of routines to account for surface snowmelt energy flux and snow masking of vegetation. Comparisons between modeled and measured surface energy fluxes of net radiation and turbulent heat showed reasonable agreement when considering measurement uncertainties in snow environments and the simplified algorithm used for the snow surface heat flux, particularly on a daily basis. There was generally better performance over the aspen field site, likely due to more reliable input data of snow depth/snow cover. The model was robust in capturing the evolution of surface energy fluxes during melt periods. The model behavior was also consistent with previous studies that indicate the occurrence of upward sensible heat fluxes during daytime owing to solar heating of vegetation limbs and branches, which often exceeds the downward sensible heat flux driving the snowmelt. However, model simulations over aspen trees showed that the upward sensible heat flux could be reversed for a lower canopy fraction owing to the dominance of downward sensible heat flux over snow. This indicates that reliable vegetation or snow cover fraction inputs to the model are needed for estimating fluxes over snow-covered landscapes.

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 Footprint issues in scintillometry over heterogeneous landscapes

2009 ◽  
Vol 6 (2) ◽  
pp. 2099-2127 ◽  
Author(s):  
W. J. Timmermans ◽  
Z. Su ◽  
A. Olioso
Keyword(s):  
Heat Flux ◽  
Time Series ◽  
Sensible Heat Flux ◽  
Simulated Data ◽  
Heat Fluxes ◽  
Two Dimensional ◽  
Sensible Heat ◽  
Heterogeneous Landscapes ◽  
Heterogeneous Landscape ◽  
Potential Tool

Abstract. Scintillometry is widely recognized as a potential tool for obtaining spatially aggregated sensible heat fluxes. Although many investigations have been made over contrasting component surfaces, few aggregation schemes consider footprint contributions. In this paper an approach is presented to infer average sensible heat flux over a very heterogeneous landscape by using a large aperture scintillometer. The methodology is demonstrated on simulated data and tested on a time series of measurements obtained during the SPARC2004 experiment in Barrax, Spain. Results show that the two-dimensional footprint approach yields more accurate results of aggregated sensible heat flux than traditional methods.

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.

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