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 Sensible Heat Observations Reveal Soil-Water Evaporation Dynamics

2008 ◽  
Vol 9 (1) ◽  
pp. 165-171 ◽  
Author(s):  
J. L. Heitman ◽  
R. Horton ◽  
T. J. Sauer ◽  
T. M. DeSutter
Keyword(s):  
Heat Flux ◽  
Soil Water ◽  
Heat Balance ◽  
Measurement Techniques ◽  
Sensible Heat Flux ◽  
Soil Surface ◽  
Water Evaporation ◽  
Sensible Heat ◽  
Near Surface ◽  
Evaporation Zone

Abstract Soil-water evaporation is important at scales ranging from microbial ecology to large-scale climate. Yet routine measurements are unable to capture rapidly shifting near-surface soil heat and water processes involved in soil-water evaporation. The objective of this study was to determine the depth and location of the evaporation zone within soil. Three-needle heat-pulse sensors were used to monitor soil heat capacity, thermal conductivity, and temperature below a bare soil surface in central Iowa during natural wetting/drying cycles. Soil heat flux and changes in heat storage were calculated from these data to obtain a balance of sensible heat components. The residual from this balance, attributed to latent heat from water vaporization, provides an estimate of in situ soil-water evaporation. As the soil dried following rainfall, results show divergence in the soil sensible heat flux with depth. Divergence in the heat flux indicates the location of a heat sink associated with soil-water evaporation. Evaporation estimates from the sensible heat balance provide depth and time patterns consistent with observed soil-water depletion patterns. Immediately after rainfall, evaporation occurred near the soil surface. Within 6 days after rainfall, the evaporation zone proceeded > 13 mm into the soil profile. Evaporation rates at the 3-mm depth reached peak values > 0.25 mm h−1. Evaporation occurred simultaneously at multiple measured depth increments, but with time lag between peak evaporation rates for depths deeper below the soil surface. Implementation of finescale measurement techniques for the soil sensible heat balance provides a new opportunity to improve understanding of soil-water evaporation.

scholarly journals Intercomparison and assessment of turbulent and physiological exchange parameters of grassland

2009 ◽  
Vol 6 (1) ◽  
pp. 241-290 ◽  
Author(s):  
E. Nemitz ◽  
K. J. Hargreaves ◽  
A. Neftel ◽  
B. Loubet ◽  
P. Cellier ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Friction Velocity ◽  
Sensible Heat Flux ◽  
Canopy Temperature ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Lower Saxony ◽  
Large Variability

Abstract. Commonly, the micrometeorological parameters that underline the calculations of surface atmosphere exchange fluxes (e.g. friction velocity and sensible heat flux) and parameters used to model exchange fluxes with SVAT-type parameterisations (e.g. latent heat flux and canopy temperature) are measured with a single set of instrumentation and are analysed with a single methodology. This paper evaluates uncertainties in these measurements with a single instrument, by comparing the independent results from nine different institutes during the international GRAMINAE integrated field experiment over agricultural grassland near Braunschweig, Lower Saxony, Germany. The paper discusses uncertainties in measuring friction velocity, sensible and latent heat fluxes, canopy temperature and investigates the energy balance closure at this site. Although individual 15-min flux calculations show a large variability between the instruments, when averaged over the campaign, fluxes agree within 2% for momentum and 11% for sensible heat. However, the spread in estimates of latent heat flux (λE) is larger, with standard deviations of averages of 18%. While the dataset averaged over the different instruments fails to close the energy budget by 30%, if the largest turbulent fluxes are considered, near perfect energy closure can be achieved, suggesting that most techniques underestimate λE in particular. The uncertainty in λE feeds results in an uncertainty in the bulk stomatal resistance, which further adds to the uncertainties in the estimation of the canopy temperature that controls the exchange. The paper demonstrated how a consensus dataset was derived, which is used by the individual investigators to calculate fluxes and drive their models.

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 A New Procedure Based on Surface Renewal Analysis to Estimate Sensible Heat Flux: A Case Study over Grapevines

2010 ◽  
Vol 11 (2) ◽  
pp. 496-508 ◽  
Author(s):  
F. Castellví ◽  
R. L. Snyder
Keyword(s):  
Heat Flux ◽  
Low Cost ◽  
Sonic Anemometer ◽  
Sensible Heat Flux ◽  
Energy Balance Equation ◽  
Sensible Heat ◽  
Surface Renewal ◽  
The Stability ◽  
Crop Coefficients ◽  
A Site

Abstract Grapevines are grown on a range of soils and in different climates. Depending on the desired final product and method of harvesting, the trellis system, and hence vineyard architecture, varies dramatically. Consequently, the crop coefficients used to estimate vineyard evapotranspiration from reference evapotranspiration are less universal than for other crops. Evapotranspiration measurements are often limited because of a lack of fetch and unavailability of vine parameters required as input. In this paper, a new procedure based on surface renewal (SR) analysis was derived to estimate sensible heat flux over the grapevines. A two-dimensional sonic anemometer operating close to the canopy can provide the inputs required to estimate the sensible heat flux and the work of expansion of the air parcels under constant pressure. Regardless of the stability conditions, the SR estimates were comparable to those determined using the eddy covariance (EC) method providing a root-mean-square error of 14 W m−2 for all data. Thus, the procedure is low cost and makes SR a simpler method than EC to estimate latent heat flux as the residual of the energy balance equation in moderately tall and heterogeneous crops. The experiment was carried out at a site influenced by regional advection of sensible heat flux.

scholarly journals Intercomparison and assessment of turbulent and physiological exchange parameters of grassland

2009 ◽  
Vol 6 (8) ◽  
pp. 1445-1466 ◽  
Author(s):  
E. Nemitz ◽  
K. J. Hargreaves ◽  
A. Neftel ◽  
B. Loubet ◽  
P. Cellier ◽  
...  
Keyword(s):  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Friction Velocity ◽  
Sensible Heat Flux ◽  
Canopy Temperature ◽  
Heat Fluxes ◽  
Sensible Heat ◽  
Large Variability ◽  
The Individual

Abstract. Commonly, the micrometeorological parameters that underline the calculations of surface atmosphere exchange fluxes (e.g. friction velocity and sensible heat flux) and parameters used to model exchange fluxes with SVAT-type parameterisations (e.g. latent heat flux and canopy temperature) are measured with a single set of instrumentation and are analysed with a single methodology. This paper evaluates uncertainties in these measurements with a single instrument, by comparing the independent results from nine different institutes during the international GRAMINAE integrated field experiment over agricultural grassland near Braunschweig, Lower Saxony, Germany. The paper discusses uncertainties in measuring friction velocity, sensible and latent heat fluxes, canopy temperature and investigates the energy balance closure at this site. Although individual 15-min flux calculations show a large variability between the instruments, when averaged over the campaign, fluxes agree within 2% for momentum and 11% for sensible heat. However, the spread in estimates of latent heat flux (λE) is larger, with standard deviations of averages of 18%. The dataset averaged over the different instruments fails to close the energy budget by 20%, significantly larger than the uncertainties in the individual flux corrections. However, if the largest individual turbulent flux estimates are considered, energy closure can be achieved, indicating that the closure gap is within the spread of the measurements. The uncertainty in λE feeds results in an uncertainty in the bulk stomatal resistance, which further adds to the uncertainties in the estimation of the canopy temperature that controls the exchange. The paper demonstrated how a consensus dataset was derived, which is used by the individual investigators to calculate fluxes and drive their models.

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