scholarly journals Significant Decrease of Uncertainties in Sensible Heat Flux Simulation Using Temporally Variable Aerodynamic Roughness in Two Typical Forest Ecosystems of China

2012 ◽  
Vol 51 (6) ◽  
pp. 1099-1110 ◽  
Author(s):  
Yanlian Zhou ◽  
Weimin Ju ◽  
Xiaomin Sun ◽  
Xuefa Wen ◽  
Dexin Guan
Keyword(s):  
Heat Flux ◽  
Roughness Length ◽  
Aerodynamic Resistance ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Sensible Heat ◽  
Atmospheric Stratification ◽  
Thermal Roughness Length ◽  
Aerodynamic Roughness ◽  
Simulation Errors

AbstractAerodynamic roughness length zom is an important parameter for reliably simulating surface fluxes. It varies with wind speed, atmospheric stratification, terrain, and other factors. However, it is usually considered a constant. It is known that uncertainties in zom result in latent heat flux (LE) simulation errors, since zom links LE with aerodynamic resistance. The effects of zom on sensible heat flux (SH) simulation are usually neglected because there is no direct link between the two. By comparing SH simulations with three types of zom inputs, it is found that allowing zom temporal variation in an SH simulation model significantly improves agreement between simulated and measured SH and also decreases the sensitivity of the SH model to the heat transfer coefficient Ct, which in turn determines the linkage between zom and thermal roughness length zoh.

Regional sensible heat flux and thermal roughness length of an inhomogeneous landscape

1998 ◽  
Vol 12 (13-14) ◽  
pp. 2115-2131 ◽  
Author(s):  
Meelis Mölder ◽  
Michiaki Sugita ◽  
Tetsuya Hiyama ◽  
Hans Bergström
Keyword(s):  
Heat Flux ◽  
Roughness Length ◽  
Sensible Heat Flux ◽  
Sensible Heat ◽  
Thermal Roughness Length

scholarly journals Evaluation of Turbulent Surface Flux Parameterizations over Tall Grass in a Beijing Suburb

2013 ◽  
Vol 14 (5) ◽  
pp. 1620-1635 ◽  
Author(s):  
Linlin Wang ◽  
Zhiqiu Gao ◽  
Zaitao Pan ◽  
Xiaofeng Guo ◽  
Elie Bou-Zeid
Keyword(s):  
Heat Flux ◽  
Roughness Length ◽  
Sensible Heat Flux ◽  
Anthropogenic Sources ◽  
Weather Data ◽  
Computational Time ◽  
Sensible Heat ◽  
Tall Grass ◽  
Thermal Roughness Length ◽  
Beijing Suburb

Abstract Numerical weather and climate prediction systems necessitate accurate land surface–atmosphere fluxes, whose determination typically replies on a suite of parameterization schemes. The authors present a field investigation over tall grass in a Beijing suburb, where the aerodynamic roughness length (z0) and zero-plane displacement height (d) are found to be 0.02 and 0.44 m, respectively (the value of d is close to two-thirds the average grass height during this field experiment). Both z0 and d values are then used as input parameters of an analytic model of flux footprint; the footprint model reveals that eddy-covariance flux measurements are mainly representative of the tall grass surface concerned herein, potential influences from anthropogenic sources in this suburban area notwithstanding. Based on the “fair weather” data (with an energy balance ratio of 0.89), the authors evaluate four parameterizations of turbulent surface fluxes, namely, a total of three traditional “iterative” schemes and one “noniterative” scheme developed recently to reduce computational time. Their performances are intercompared in terms of the estimations of the sensible heat flux and two turbulence components (the friction velocity and temperature scale). In weakly stable to unstable conditions, two schemes are recommended here for their good performance overall; the first scheme stems jointly from the work of Högström and Beljaars and Holtslag, and the second stems from that of Li et al.. For this tall grass surface, the choice of z0/z0h = 100 (z0h is the thermal roughness length) is more appropriate than another choice of 10, because the former produces comparatively accurate sensible heat flux estimations.

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.

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 Surface Roughness and Bulk Heat Transfer on a Glacier: Comparison with Eddy Correlation

1989 ◽  
Vol 35 (121) ◽  
pp. 343-348 ◽  
Author(s):  
D. Scott Munro
Keyword(s):  
Roughness Length ◽  
Profile Analysis ◽  
Sensible Heat Flux ◽  
Eddy Correlation ◽  
Suitable Model ◽  
Thermal Roughness Length ◽  
Roughness Lengths ◽  
Glacier Ice ◽  
Measurement Height ◽  
Aerodynamic Roughness

AbstractMore than 100 simultaneously measured profiles of wind speed and temperature were analyzed to determine the aerodynamic and thermal roughness lengths of glacier ice. The results proved to be extremely sensitive to measurement height, which is difficult to define precisely on the hummocky terrain of a glacier. Therefore, aerodynamic roughness lengths were estimated from the microtopography of the surface, yielding 2.46 mm for ice, and 5.5 mm for snow. Despite the indeterminate nature of the profile analysis, it did support the view that the thermal roughness length must decrease as the roughness Reynolds number increases, a relationship which has been modelled in the literature. Good agreement between bulk-transfer estimates and eddy-correlation measurements of fhe sensible heat-flux density on melting ice and snow was obtained by combining the aerodynamic roughness length with a suitable model for thermal roughness length.

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.

Turbulent Flux Transfer over Bare-Soil Surfaces: Characteristics and Parameterization

2008 ◽  
Vol 47 (1) ◽  
pp. 276-290 ◽  
Author(s):  
Kun Yang ◽  
Toshio Koike ◽  
Hirohiko Ishikawa ◽  
Joon Kim ◽  
Xin Li ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Transfer Coefficient ◽  
Roughness Length ◽  
Turbulent Flux ◽  
Sensible Heat Flux ◽  
Bare Soil ◽  
Mean Values ◽  
Thermal Roughness Length ◽  
Aerodynamic Roughness ◽  
The Individual

Abstract Parameterization of turbulent flux from bare-soil and undercanopy surfaces is imperative for modeling land–atmosphere interactions in arid and semiarid regions, where flux from the ground is dominant or comparable to canopy-sourced flux. This paper presents the major characteristics of turbulent flux transfers over seven bare-soil surfaces. These sites are located in arid, semiarid, and semihumid regions in Asia and represent a variety of conditions for aerodynamic roughness length (z0m; from <1 to 10 mm) and sensible heat flux (from −50 to 400 W m−2). For each site, parameter kB−1 [=ln(z0m/z0h), where z0h is the thermal roughness length] exhibits clear diurnal variations with higher values during the day and lower values at night. Mean values of z0h for the individual sites do not change significantly with z0m, resulting in kB−1 increasing with z0m, and thus the momentum transfer coefficient increases faster than the heat transfer coefficient with z0m. The term kB−1 often becomes negative at night for relatively smooth surfaces (z0m ∼ 1 mm), indicating that the widely accepted excess resistance for heat transfer can be negative, which cannot be explained by current theories for aerodynamically rough surfaces. Last, several kB−1 schemes are evaluated using the same datasets. The results indicate that a scheme that can reproduce the diurnal variation of kB−1 generally performs better than schemes that cannot.

scholarly journals Simulating the IHOP_2002 Fair-Weather CBL with the WRF-ARW–Noah Modeling System. Part I: Surface Fluxes and CBL Structure and Evolution along the Eastern Track

2010 ◽  
Vol 138 (3) ◽  
pp. 722-744 ◽  
Author(s):  
Margaret A. LeMone ◽  
Fei Chen ◽  
Mukul Tewari ◽  
Jimy Dudhia ◽  
Bart Geerts ◽  
...  
Keyword(s):  
Heat Flux ◽  
Land Surface ◽  
Roughness Length ◽  
Vegetation Type ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Weather Data ◽  
Surface Model ◽  
Fair Weather ◽  
Convective Boundary

Abstract Fair-weather data from the May–June 2002 International H2O Project (IHOP_2002) 46-km eastern flight track in southeast Kansas are compared to simulations using the advanced research version of the Weather Research and Forecasting model coupled to the Noah land surface model (LSM), to gain insight into how the surface influences convective boundary layer (CBL) fluxes and structure, and to evaluate the success of the modeling system in representing CBL structure and evolution. This offers a unique look at the capability of the model on scales the length of the flight track (46 km) and smaller under relatively uncomplicated meteorological conditions. It is found that the modeled sensible heat flux H is significantly larger than observed, while the latent heat flux (LE) is much closer to observations. The slope of the best-fit line ΔLE/ΔH to a plot of LE as a function of H, an indicator of horizontal variation in available energy H + LE, for the data along the flight track, was shallower than observed. In a previous study of the IHOP_2002 western track, similar results were explained by too small a value of the parameter C in the Zilitinkevich equation used in the Noah LSM to compute the roughness length for heat and moisture flux from the roughness length for momentum, which is supplied in an input table; evidence is presented that this is true for the eastern track as well. The horizontal variability in modeled fluxes follows the soil moisture pattern rather than vegetation type, as is observed; because the input land use map does not capture the observed variation in vegetation. The observed westward rise in CBL depth is successfully modeled for 3 of the 4 days, but the actual depths are too high, largely because modeled H is too high. The model reproduces the timing of observed cumulus cloudiness for 3 of the 4 days. Modeled clouds lead to departures from the typical clear-sky straight line relating surface H to LE for a given model time, making them easy to detect. With spatial filtering, a straight slope line can be recovered. Similarly, larger filter lengths are needed to produce a stable slope for observed fluxes when there are clouds than for clear skies.

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