scholarly journals An Assessment of Coordinate Rotation Methods in Sonic Anemometer Measurements of Turbulent Fluxes over Complex Mountainous Terrain

Atmosphere ◽  
2019 ◽  
Vol 10 (6) ◽  
pp. 324 ◽  
Author(s):  
Alessio Golzio ◽  
Irene Maria Bollati ◽  
Silvia Ferrarese
Keyword(s):  
Quality Assessment ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Stationary Flow ◽  
Turbulent Fluxes ◽  
Quality Level ◽  
Mountainous Terrain ◽  
Sensible Heat ◽  
Coordinate Rotation ◽  
Ultrasonic Anemometer

The measurement of turbulent fluxes in the atmospheric boundary layer is usually performed using fast anemometers and the Eddy Covariance technique. This method has been applied here and investigated in a complex mountainous terrain. A field campaign has recently been conducted at Alpe Veglia (the Central-Western Italian Alps, 1746 m a.s.l.) where both standard and micrometeorological data were collected. The measured values obtained from an ultrasonic anemometer were analysed using a filtering procedure and three different coordinate rotation procedures: Double (DR), Triple Rotation (TR) and Planar Fit (PF) on moving temporal windows of 30 and 60 min. A quality assessment was performed on the sensible heat and momentum fluxes and the results show that the measured turbulent fluxes at Alpe Veglia were of a medium-high quality level and rarely passed the stationary flow test. A comparison of the three coordinate procedures, using quality assessment and sensible heat flux standard deviations, revealed that DR and TR were comparable, with significant differences, mainly under low-wind conditions. The PF method failed to satisfy the physical requirement for the multiple planarity of the flow, due to the complexity of the mountainous terrain.

scholarly journals On the Temperature Structure Parameter and Sensible Heat Flux over Helsinki from Sonic Anemometry and Scintillometry

2013 ◽  
Vol 30 (8) ◽  
pp. 1604-1615 ◽  
Author(s):  
C. R. Wood ◽  
R. D. Kouznetsov ◽  
R. Gierens ◽  
A. Nordbo ◽  
L. Järvi ◽  
...  
Keyword(s):  
Heat Flux ◽  
Measurement Techniques ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Temperature Structure ◽  
Sensible Heat ◽  
Structure Parameter ◽  
Large Variability ◽  
Temperature Structure Parameter ◽  
Depth Analysis

Abstract Two commercial large-aperture scintillometers, Scintec BLS900, were tested on pathlengths of 1840 and 4200 m at about 45–65 m above ground in Helsinki, Finland. From July 2011 through June 2012, large variability in diurnal and annual cycles of both the temperature structure parameter and sensible heat flux were observed. Scintillometer data were compared with data from two eddy-covariance stations. A robust method was developed for the calculation of from raw sonic-anemometer data. In contrast to many earlier studies that solely present the values of , the main focus here is on comparisons of itself. This has advantages, because optical-wavelength scintillometers measure with few assumptions, while the determination of implies the applicability of the Monin–Obukhov similarity theory, which has several inherent limitations. The histograms of compare well between sonic and scintillometer. In-depth analysis is focused on one of the scintillometer paths: both and comparisons gave similar and surprisingly high correlation coefficients (0.85 for and 0.84–0.95 for in unstable conditions), given the differences between the two measurement techniques, substantial sensor separation, and different source areas.

scholarly journals RELAÇÃO ENTRE VELOCIDADE DO VENTO E ENERGIA CINÉTICA TURBULENTA EM MODELOS SIMPLIFICADOS DA CAMADA LIMITE NOTURNA

2016 ◽  
Vol 38 ◽  
pp. 75
Author(s):  
Rafael Maroneze ◽  
Otávio Costa Acevedo ◽  
Felipe Denardin Costa
Keyword(s):  
Heat Flux ◽  
Sensible Heat Flux ◽  
Turbulent Fluxes ◽  
Turbulent Intensity ◽  
Simplified Model ◽  
Sensible Heat ◽  
Temperature Variance ◽  
Stable Conditions ◽  
Atmospheric Coupling

The determination of the turbulent fluxes in very stable conditions is done, generally, through parameterizations. In this work the turbulent fluxes are estimated, by using a simplified model, through prognostic equations for the turbulent intensity, the sensible heat flux and the temperature variance. The results indicate that the model is able to reproduce both atmospheric coupling and the intermittent character of the turbulence in very stable conditions.

scholarly journals Quality control of CarboEurope flux data – Part 1: Coupling footprint analyses with flux data quality assessment to evaluate sites in forest ecosystems

2008 ◽  
Vol 5 (2) ◽  
pp. 433-450 ◽  
Author(s):  
M. Göckede ◽  
T. Foken ◽  
M. Aubinet ◽  
M. Aurela ◽  
J. Banza ◽  
...  
Keyword(s):  
Heat Flux ◽  
Data Quality ◽  
Quality Assessment ◽  
Eddy Covariance ◽  
Sensible Heat Flux ◽  
Measurement Data ◽  
Flux Data ◽  
Evaluation Approach ◽  
Ip Network ◽  
Coordinate Rotation

Abstract. We applied a site evaluation approach combining Lagrangian Stochastic footprint modeling with a quality assessment approach for eddy-covariance data to 25 forested sites of the CarboEurope-IP network. The analysis addresses the spatial representativeness of the flux measurements, instrumental effects on data quality, spatial patterns in the data quality, and the performance of the coordinate rotation method. Our findings demonstrate that application of a footprint filter could strengthen the CarboEurope-IP flux database, since only one third of the sites is situated in truly homogeneous terrain. Almost half of the sites experience a significant reduction in eddy-covariance data quality under certain conditions, though these effects are mostly constricted to a small portion of the dataset. Reductions in data quality of the sensible heat flux are mostly induced by characteristics of the surrounding terrain, while the latent heat flux is subject to instrumentation-related problems. The Planar-Fit coordinate rotation proved to be a reliable tool for the majority of the sites using only a single set of rotation angles. Overall, we found a high average data quality for the CarboEurope-IP network, with good representativeness of the measurement data for the specified target land cover types.

scholarly journals Micrometeorological processes driving snow ablation in an Alpine catchment

2011 ◽  
Vol 5 (4) ◽  
pp. 1083-1098 ◽  
Author(s):  
R. Mott ◽  
L. Egli ◽  
T. Grünewald ◽  
N. Dawes ◽  
C. Manes ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Energy Balance ◽  
Snow Cover ◽  
Sensible Heat Flux ◽  
Internal Boundary Layer ◽  
Turbulent Fluxes ◽  
Eddy Correlation ◽  
Internal Boundary ◽  
Sensible Heat ◽  
Regional Prediction

Abstract. Mountain snow covers typically become patchy over the course of a melting season. The snow pattern during melt is mainly governed by the end of winter snow depth distribution and the local energy balance. The objective of this study is to investigate micro-meteorological processes driving snow ablation in an Alpine catchment. For this purpose we combine a meteorological boundary-layer model (Advanced Regional Prediction System) with a fully distributed energy balance model (Alpine3D). Turbulent fluxes above melting snow are further investigated by using data from eddy-correlation systems. We compare modeled snow ablation to measured ablation rates as obtained from a series of Terrestrial Laser Scanning campaigns covering a complete ablation season. The measured ablation rates indicate that the advection of sensible heat causes locally increased ablation rates at the upwind edges of the snow patches. The effect, however, appears to be active over rather short distances of about 4–6 m. Measurements suggest that mean wind velocities of about 5 m s−1 are required for advective heat transport to increase snow ablation over a long fetch distance of about 20 m. Neglecting this effect, the model is able to capture the mean ablation rates for early ablation periods but strongly overestimates snow ablation once the fraction of snow coverage is below a critical value of approximately 0.6. While radiation dominates snow ablation early in the season, the turbulent flux contribution becomes important late in the season. Simulation results indicate that the air temperatures appear to overestimate the local air temperature above snow patches once the snow coverage is low. Measured turbulent fluxes support these findings by suggesting a stable internal boundary layer close to the snow surface causing a strong decrease of the sensible heat flux towards the snow cover. Thus, the existence of a stable internal boundary layer above a patchy snow cover exerts a dominant control on the timing and magnitude of snow ablation for patchy snow covers.

Atmospheric Response to a Partial Solar Eclipse over a Cotton Field in Central California

2007 ◽  
Vol 46 (11) ◽  
pp. 1792-1803 ◽  
Author(s):  
Matthias Mauder ◽  
R. L. Desjardins ◽  
Steven P. Oncley ◽  
Ian MacPherson
Keyword(s):  
Carbon Dioxide ◽  
Water Vapor ◽  
Wavelet Analysis ◽  
Solar Eclipse ◽  
Sensible Heat Flux ◽  
Turbulent Fluxes ◽  
Cotton Field ◽  
Sensible Heat ◽  
Central California ◽  
Partial Solar Eclipse

Abstract The partial solar eclipse on 11 July 1991 in central California, with 58.3% maximum coverage, provided an exceptional opportunity to study the temporal response of processes in the atmospheric boundary layer to an abrupt change in solar radiation. Almost laboratory-like conditions were met over a cotton field, since no clouds disturbed the course of the eclipse. Tower-based and complementing aircraft-based systems monitored the micrometeorological conditions over the site. Temperature profile measurements indicated neutral stratification during the maximum eclipse in contrast to the unstable conditions before and after the eclipse. Accordingly, the sensible heat exchange completely stopped, as a wavelet analysis of the tower measurements and airborne eddy-covariance measurements showed. Turbulent fluxes of water vapor, carbon dioxide, and ozone were reduced by approximately ⅔ at the peak of the eclipse. Wavelet analysis further indicated that the same eddies contributed to the turbulent transport of water vapor and carbon dioxide, whereas sensible heat was transported by different ones. An analysis of the decay of turbulent kinetic energy followed a power law of time with an exponent of −1.25. The response of the sensible heat flux was 8–13 min delayed relative to the solar forcing, whereas no significant time lag could be detected for the turbulent fluxes of air constituents.

scholarly journals A Feasibility Study for Determining the Sensible Heat Flux to and from Small Green Roofs

2021 ◽  
Author(s):  
Niels Wollschläger ◽  
Uwe Schlink ◽  
Armin Raabe
Keyword(s):  
Heat Flux ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Three Dimensional ◽  
Source Area ◽  
Surface Characteristics ◽  
Green Roofs ◽  
Heat Fluxes ◽  
Horizontal Wind ◽  
Sensible Heat

AbstractEddy covariance is an established technique for registering sensible heat fluxes. However, this method is less adequate for smaller surfaces that cannot match the associated footprint. As an alternative technique, a recently constructed acoustic anemometer (Ly-ATOM) is tested, which operates horizontally at an extension of circa 1 m and a data-acquisition frequency of 1 Hz. The Ly-ATOM device reproduces both the acoustic virtual temperature and the horizontal wind components registered by a three-dimensional sonic anemometer. As this Ly-ATOM device can be applied much closer to the ground compared with a sonic anemometer, the size of the related source area is significantly reduced (by a factor of 25). Two methods are used to retrieve the sensible heat flux from variance characteristics of temperature and the horizontal wind components recorded by the Ly-ATOM device: combining the flux-variance-similarity and alternative-flux-variance methods for use in unstable and stable stratification, respectively, yields good results for the sonic measurements. Therefore, these methods can be applied to the Ly-ATOM device as well. In investigating the sensitivity to detect modified surface characteristics, specifically increased evapotranspiration and decreased surface albedo, the Ly-ATOM device proves to be superior to the sonic anemometer which is more vertically removed from the surface of interest.

scholarly journals Using sonic anemometer temperature to measure sensible heat flux in strong winds

2012 ◽  
Vol 5 (1) ◽  
pp. 447-469 ◽  
Author(s):  
S. P. Burns ◽  
T. W. Horst ◽  
P. D. Blanken ◽  
R. K. Monson
Keyword(s):  
Heat Flux ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Horizontal Wind ◽  
Subalpine Forest ◽  
Sensible Heat ◽  
Scientific Model ◽  
Horizontal Wind Speed ◽  
Sonic Anemometers

Abstract. The sensible heat flux (H) is a significant component of the surface energy balance (SEB). Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (w') and sonic temperature (Ts'), and are commonly used to measure H. Our study examines 30-min heat fluxes measured with a Campbell Scientific model CSAT3 sonic anemometer above a subalpine forest. We compare H calculated with Ts to H calculated with a co-located thermocouple and find that for horizontal wind speed (U) less than 8 m s−1 the agreement is ≈±30 W m−2. However, for U >≈ 8 m s−1, the CSAT3 H becomes larger than H calculated with the thermocouple, reaching a maximum difference of ≈250 W m−2 at U ≈ 18 m s−1. H calculated with the thermocouple results in a SEB that is relatively independent of U at high wind speeds. In contrast, the SEB calculated with H from the CSAT3 varies considerably with U, particularly at night. Cospectral analysis of w'Ts' suggest that spurious correlation is a problem during high winds which leads to a positive (additive) increase in H calculated with the CSAT3. At night, when H is typically negative, this CSAT3 error results in a measured H that falsely approaches zero or even becomes positive. Within a broader context, the usefulness of side-by-side instrument comparisons are discussed.

scholarly journals Using sonic anemometer temperature to measure sensible heat flux in strong winds

2012 ◽  
Vol 5 (9) ◽  
pp. 2095-2111 ◽  
Author(s):  
S. P. Burns ◽  
T. W. Horst ◽  
L. Jacobsen ◽  
P. D. Blanken ◽  
R. K. Monson
Keyword(s):  
Heat Flux ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Heat Fluxes ◽  
Horizontal Wind ◽  
Subalpine Forest ◽  
Sensible Heat ◽  
Horizontal Wind Speed ◽  
Sonic Anemometers ◽  
Significant Underestimation

Abstract. Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (w') and sonic temperature (Ts'), and are commonly used to measure sensible heat flux (H). Our study examines 30-min heat fluxes measured with a Campbell Scientific CSAT3 sonic anemometer above a subalpine forest. We compared H calculated with Ts to H calculated with a co-located thermocouple and found that, for horizontal wind speed (U) less than 8 m s−1, the agreement was around ±30 W m−2. However, for U ≈ 8 m s−1, the CSAT H had a generally positive deviation from H calculated with the thermocouple, reaching a maximum difference of ≈250 W m−2 at U ≈ 18 m s−1. With version 4 of the CSAT firmware, we found significant underestimation of the speed of sound and thus Ts in high winds (due to a delayed detection of the sonic pulse), which resulted in the large CSAT heat flux errors. Although this Ts error is qualitatively similar to the well-known fundamental correction for the crosswind component, it is quantitatively different and directly related to the firmware estimation of the pulse arrival time. For a CSAT running version 3 of the firmware, there does not appear to be a significant underestimation of Ts; however, a Ts error similar to that of version 4 may occur if the CSAT is sufficiently out of calibration. An empirical correction to the CSAT heat flux that is consistent with our conceptual understanding of the Ts error is presented. Within a broader context, the surface energy balance is used to evaluate the heat flux measurements, and the usefulness of side-by-side instrument comparisons is discussed.

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.

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