scholarly journals Accuracy of Measurements of Turbulent Phenomena in the Surface Layer with an Ultrasonic Anemometer

2006 ◽  
Vol 23 (6) ◽  
pp. 785-801 ◽  
Author(s):  
D. Contini ◽  
A. Donateo ◽  
F. Belosi
Keyword(s):  
Surface Layer ◽  
Wind Velocity ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Design Parameters ◽  
Sensible Heat ◽  
Random Uncertainty ◽  
Accuracy Of Measurements ◽  
Ultrasonic Anemometer ◽  
Averaging Time

Abstract Ultrasonic anemometers are widely used to investigate turbulence in the surface layer. Some of their advantages are high-frequency sampling, the ability to work for long periods without a resident operator (even in adverse meteorological conditions), and their calibration related only to design parameters. In this paper an analysis of the random uncertainty associated with ultrasonic anemometer measurements is reported. The analysis is based on a statistical procedure that compares the simultaneous data taken with two identical anemometers operating in nominally identical conditions. Postprocessing of data has been carried out in different reference systems in order to evaluate how the random uncertainties change according to the postprocessing procedure used. Results show that uncertainty on wind velocity decreases with averaging time, and it can be as low as 1 cm s−1 for a typical averaging time of 30 min. The random uncertainty on average vertical wind velocity 〈w〉 could also be as low as 1 cm s−1, and it is very sensitive to the effects of vertical misalignment. The analysis is based on six different measurement sets in which the anemometers have been deployed on a single mast or in two separate masts with and without additional detectors placed near the anemometers themselves. Results indicate that the uncertainty of all the measured parameters increases when the anemometer is used in configurations in which they are placed on separate masts. Several parameters also show an additional increase of uncertainty if other detectors are placed nearby. The relative random uncertainty on momentum and sensible heat fluxes, for typical averaging time, can be as low as 6%–7% and it could increase to a factor of 2–3 when they are placed on separate masts. Only small effects due to the influence of flow distortions caused by the presence of additional sensors have been found on fluxes and are mainly related to sensible heat flux.

scholarly journals Sensible Heat Fluxes in the Nearly Neutral Boundary Layer: The Impact of Frictional Heating within the Surface Layer

2019 ◽  
Vol 76 (4) ◽  
pp. 1039-1053
Author(s):  
J. M. Edwards
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Frictional Heating ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Simple Modification ◽  
Neutral Boundary Layer ◽  
The Impact

Abstract The effect of frictional dissipative heating on the calculation of surface fluxes in the atmospheric boundary layer using bulk flux formulas is considered. Although the importance of frictional dissipation in intense storms has been widely recognized, it is suggested here that its impact is also to be seen at more moderate wind speeds in apparently enhanced heat transfer coefficients and countergradient fluxes in nearly neutral conditions. A simple modification to the bulk flux formula can be made to account for its impact within the surface layer. This modification is consistent with an interpretation of the surface layer as one across which the flux of total energy is constant. The effect of this modification on tropical cyclones is assessed in an idealized model, where it is shown to reduce the predicted maximum wind speed by about 4%. In numerical simulations of three individual storms, the impacts are more subtle but indicate a reduction of the sensible heat flux into the storm and a cooling of the surface layer.

scholarly journals The evaluating study of the momentum and heat exchange process of two surface layer schemes during the severe haze pollution in east China

2018 ◽  
Author(s):  
Yue Peng ◽  
Hong Wang ◽  
Yubin Li ◽  
Changwei Liu ◽  
Tianliang Zhao ◽  
...  
Keyword(s):  
Heat Flux ◽  
Surface Layer ◽  
Momentum Flux ◽  
Roughness Length ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Chemical Model ◽  
East China ◽  
Sensible Heat ◽  
Haze Pollution

Abstract. The turbulent flux parameterization schemes in surface layer are crucial for air pollution modeling. The pollutants prediction by atmosphere chemical model exist obvious deficiencies, which may be closely related to the uncertainties of the momentum and sensible heat fluxes calculation in the surface layer. In this study, a new surface layer scheme (Li) and a classic scheme (MM5) were compared and evaluated based on the observed momentum and sensible heat fluxes in east China during a severe haze episode in winter. The results showed that it is necessary to distinguish the thermal roughness length z0h from the aerodynamic roughness length z0m, and ignoring the difference between the two led to large errors of the momentum and sensible heat fluxes in MM5. The error of calculated sensible heat flux was reduced by 54 % after discriminating z0h from z0m in MM5. Besides, the algorithm itself of Li scheme performed generally better than MM5 in winter in east China and the momentum flux bias of the Li scheme was lower about 12%, sensible heat flux bias about 5 % than those of MM5 scheme. Most of all, the Li scheme showed a significant advantage over MM5 for the transition stage from unstable to stable atmosphere corresponding to the PM2.5 accumulation. The momentum flux bias of Li was lower about 38 %, sensible heat flux bias about 43 % than those of MM5 during the PM2.5 increasing stage. This study result indicates the ability of Li scheme for more accurate describing the regional atmosphere stratification, and suggests the potential improving possibilities of severe haze prediction in east China by online coupling it into the atmosphere chemical model.

scholarly journals Seasonal and diurnal variations in moisture, heat and CO2 fluxes over a typical steppe prairie in Inner Mongolia, China

2009 ◽  
Vol 13 (7) ◽  
pp. 987-998 ◽  
Author(s):  
Z. Gao ◽  
D. H. Lenschow ◽  
Z. He ◽  
M. Zhou
Keyword(s):  
Inner Mongolia ◽  
Surface Albedo ◽  
Sensible Heat Flux ◽  
Experimental Period ◽  
Diurnal Variations ◽  
Heat Fluxes ◽  
Co2 Fluxes ◽  
Sensible Heat ◽  
Eddy Covariance Method ◽  
Seasonal And Diurnal Variations

Abstract. In order to examine energy partitioning and CO2 exchange over a steppe prairie in Inner Mongolia, China, fluxes of moisture, heat and CO2 in the surface layer from June 2007 through June 2008 were calculated using the eddy covariance method. The study site was homogenous and approximately 1500 m×1500 m in size. Seasonal and diurnal variations in radiation components, energy components and CO2 fluxes are examined. Results show that all four radiation components changed seasonally, resulting in a seasonal variation in net radiation. The radiation components also changed diurnally. Winter surface albedo was higher than summer surface albedo because during winter the snow-covered surface increased the surface albedo. The seasonal variations in both sensible heat and CO2 fluxes were stronger than those of latent heat and soil heat fluxes. Sensible heat flux was the main consumer of available energy for the entire experimental period. The energy imbalance problem was encountered and the causes are analyzed.

scholarly journals Disentangling the response of forest and grassland energy exchange to heatwaves under idealized land–atmosphere coupling

2014 ◽  
Vol 11 (4) ◽  
pp. 5969-5995
Author(s):  
C. C. van Heerwaarden ◽  
A. J. Teuling
Keyword(s):  
Heat Wave ◽  
Heat Waves ◽  
Dynamic Properties ◽  
Sensible Heat Flux ◽  
Early Morning ◽  
Stomatal Resistance ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Area Index ◽  
Wave Conditions

Abstract. This study investigates the difference in land–atmosphere interactions between grassland and forest during typical heat wave conditions in order to understand the controversial results of Teuling et al. (2010) (T10, hereafter), who have found the systematic occurrence of higher sensible heat fluxes over forest than over grassland during heat wave conditions. With a simple, but accurate coupled land–atmosphere model, we are able to reproduce the findings of T10 for both normal summer and heat wave conditions, and to carefully explore the sensitivity of the coupled land–atmosphere system to changes in incoming radiation and early-morning temperature. Our results emphasize the importance of fast processes during the onset of heat waves, since we are able to explain the results of T10 without having to take into account changes in soil moisture. In order to disentangle the contribution of differences in several static and dynamic properties between forest and grassland, we have performed an experiment in which new land use types are created that are equal to grassland, but with one of its properties replaced by that of forest. From these, we conclude that the closure of stomata in the presence of dry air is by far the most important process in creating the different behavior of grassland and forest during the onset of a heat wave. However, we conclude that for a full explanation of the results of T10 also the other properties (albedo, roughness and the ratio of minimum stomatal resistance to leaf-area index) play an important, but indirect role; their influences mainly consist of strengthening the feedback that leads to the closure of the stomata by providing more energy that can be converted into sensible heat. The model experiment also confirms that, in line with the larger sensible heat flux, higher atmospheric temperatures occur over forest.

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 Evaluating the performance of two surface layer schemes for the momentum and heat exchange processes during severe haze pollution in Jing-Jin-Ji in eastern China

2018 ◽  
Vol 18 (23) ◽  
pp. 17421-17435 ◽  
Author(s):  
Yue Peng ◽  
Hong Wang ◽  
Yubin Li ◽  
Changwei Liu ◽  
Tianliang Zhao ◽  
...  
Keyword(s):  
Surface Layer ◽  
Roughness Length ◽  
Turbulent Flux ◽  
Eastern China ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Chemical Models ◽  
Atmospheric Stratification ◽  
Haze Pollution ◽  
Thermal Roughness Length

Abstract. The turbulent flux parameterization schemes in the surface layer are crucial for air pollution modeling. There have been some deficiencies in the prediction of air pollutants by atmosphere chemical models, which is closely related to the uncertainties of the momentum and sensible heat fluxes calculated in the surface layer. The differences between two surface layer schemes (Li and MM5 schemes) were discussed, and the performances of two schemes were mainly evaluated based on the observed momentum and sensible heat fluxes during a heavy haze episode in Jing-Jin-Ji in eastern China. The results showed that the aerodynamic roughness length z0m and the thermal roughness length z0h played major roles in the flux calculation. Compared with the Li scheme, ignoring the difference between z0m and z0h in the MM5 scheme induced a great error in the calculation of the sensible heat flux (e.g., the error was 54 % at Gucheng station). Besides the roughness length, the algorithm for the surface turbulent flux as well as the roughness sublayer also resulted in certain errors in the MM5 scheme. In addition, magnitudes of z0m and z0h have significant influence on the two schemes. The large z0m and z0m∕z0h in megacities with a rough surface (e.g., Beijing) resulted in much larger differences of momentum and sensible heat fluxes between Li and MM5, compared with the small z0m and z0m∕z0h in suburban areas with a smooth surface (e.g., Gucheng). The Li scheme could better characterize the evolution of atmospheric stratification than the MM5 scheme in general, especially for the transition stage from unstable to stable atmospheric stratification, corresponding to the PM2.5 accumulation. The biases of momentum and sensible heat fluxes from Li were lower, about 38 % and 43 %, respectively, than those from MM5 during this stage. This study indicates the superiority of the Li scheme in describing regional atmospheric stratification and an improved possibility of severe haze prediction in Jing-Jin-Ji in eastern China by coupling it into atmosphere chemical models.

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.

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