Obtaining Surface Momentum and Sensible Heat Fluxes from Crosswind Scintillometers

Andreas, Edgar L.

doi:10.1175/1520-0426(2000)017<0003:osmash>2.0.co;2

Cited by 6 publications

(5 citation statements)

References 34 publications

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“…Such path-integrated measures have been developed using laser-scintillometers (Nakaya et al, 2007) and acoustic travel-time tomography (Barth et al, 2007). Unfortunately, these measurement techniques possess wind speed detection limits of about 0.2 m s −1 , and thus are not sensitive enough to describe the turbulence during stable and very stable conditions (Andreas, 2000). Furthermore, some of these methods depend on the validity of MoninObukhov similarity theory (MOST) which generally fails under stable conditions.…”

Section: Introductionmentioning

confidence: 99%

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions

et al. 2012

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Abstract. Measurements of land-surface emission rates of greenhouse and other gases at large spatial scales (10 000 m 2 ) are needed to assess the spatial distribution of emissions. This can be readily done using spatial-integrating micrometeorological methods like flux-gradient methods which were evaluated for determining land-surface emission rates of trace gases under stable boundary layers. Non-intrusive path-integrating measurements are utilized. Successful application of a flux-gradient method requires confidence in the gradients of trace gas concentration and wind, and in the applicability of boundary-layer turbulence theory; consequently the procedures to qualify measurements that can be used to determine the flux is critical. While there is relatively high confidence in flux measurements made under unstable atmospheres with mean winds greater than 1 m s −1 , there is greater uncertainty in flux measurements made under free convective or stable conditions. The study of N 2 O emissions of flat grassland and NH 3 emissions from a cattle lagoon involves quality-assured determinations of fluxes under low wind, stable or night-time atmospheric conditions when the continuous "steady-state" turbulence of the surface boundary layer breaks down and the layer has intermittent turbulence. Results indicate that following the Monin-Obukhov similarity theory (MOST) flux-gradient methods that assume a loglinear profile of the wind speed and concentration gradient incorrectly determine vertical profiles and thus flux in the stable boundary layer. An alternative approach is considered on the basis of turbulent diffusivity, i.e. the measured friction velocity as well as height gradients of horizontal wind speeds and concentrations without MOST correction for stability. It is shown that this is the most accurate of the flux-gradient methods under stable conditions.

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Section: Introductionmentioning

confidence: 99%

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions

et al. 2012

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“…In the future, by applying two scintillometers with paths perpendicular to each other, not only U ⊥ but also the wind direction and horizontal wind speed could be estimated (Andreas, 2000), thereby obtaining an area-averaged value of the horizontal wind speed and wind direction above an urban environment. Compared to a Doppler lidar the scintillometer is less expensive and easier to use.…”

Section: Discussionmentioning

confidence: 99%

Observing crosswind over urban terrain using scintillometer and Doppler lidar

Dinther¹,

Wood²,

Hartogensis³

et al. 2014

Preprint

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Abstract. In this study, the crosswind (wind component perpendicular to a path, U&bot;) is measured by a scintillometer and Doppler lidar above the urban environment of Helsinki, Finland, for 3 weeks. The scintillometer allows acquisition of a path-averaged value of U&bot; (U&bot;), while the Doppler lidar allows acquisition of path-resolved U&bot; (U&bot; (x), where x is the position along the path). The goal of this study is to evaluate the applicability of scintillometer U&bot;-measurements for conditions where U&bot; (x) is variable. If the scintillometer is applicable in such variable-wind conditions, it can also be used in the urban environment. Two methods were applied to obtain U&bot; from the scintillometer signal; the cumulative spectrum method (relies on scintillation spectra), and the lookup table method (relies on time-lagged correlation functions). Both methods compared reasonably well with the Doppler lidar measurements, especially considering the challenging urban environment in which they were measuring; with RMSE of 0.71 and 0.73 m s−1. This indicates that both measurement technologies are able to obtain U&bot; in the complex urban environment. The in detail investigation of four cases indicate that the cumulative spectrum method is less susceptible to a variable U&bot; (x) than the lookup table method. However, the lookup table method can be adjusted to improve its capabilities to obtain U&bot; for conditions where U&bot; (x) is variable.

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“…The sensitivity analysis will be carried out similarly to that of Andreas [2000], where the relative change in the resulting variable is expressed in terms of a linear combination of the relative changes in the input variables. If Y is the resulting variable, and X i ( i = 1,2,… N ) are the N input variables, the relative change in Y can be expressed as where is defined as the sensitivity coefficient of Y to X i .…”

Section: Applicabilitymentioning

confidence: 99%

“…[22] The sensitivity analysis will be carried out similarly to that of Andreas [2000], where the relative change in the resulting variable is expressed in terms of a linear combination of the relative changes in the input variables. If Y is the resulting variable, and X i (i = 1,2,. .…”

Section: Sensitivitymentioning

confidence: 99%

Hydrometeorological application of a microwave link: 1. Evaporation

Leijnse

Uijlenhoet

Stricker

2007

Water Resources Research

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[1] A method to estimate areal evaporation using a microwave link (radio wave scintillometer) in combination with an energy budget constraint is proposed. This radio wave scintillometry-energy budget method (RWS-EBM) is evaluated for its applicability in different meteorological conditions and for its sensitivity to various variables (the structure parameter of the refractive index of air C n 2 , the total available energy R n À G, the wind velocity u, the effective average vegetation height h 0 , and the correlation coefficient between the temperature and humidity fluctuations r TQ ). The method is shown to be best suited for use in wet to moderately dry conditions, where the latent heat flux is at least a third of the total available energy (i.e., Bowen ratio 2). It is important to accurately measure the total available energy and the wind velocity as the RWS-EBM is most sensitive to these variables. The Flevoland field experiment has provided the data, obtained with a 27-GHz radio wave scintillometer (over 2.2 km), a large-aperture scintillometer (also 2.2 km), and four eddy covariance systems, which are used to test the RWS-EBM. Comparing 92 daytime measurements (30-min intervals) of the evaporation estimated using the RWS-EBM to that determined in alternative manners (eddy covariance and two-wavelength scintillometry) leads to the conclusion that the method provides consistent estimates (coefficient of determination r 2 = 0.85 in both cases) under relatively wet conditions.

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Obtaining Surface Momentum and Sensible Heat Fluxes from Crosswind Scintillometers

Cited by 6 publications

References 34 publications

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions

Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions

Observing crosswind over urban terrain using scintillometer and Doppler lidar

Hydrometeorological application of a microwave link: 1. Evaporation

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