Richardson number profiles through shear instability wave regions observed in the lower planetary boundary layer

Emmanuel, C. B.

doi:10.1007/bf02188308

Cited by 32 publications

(16 citation statements)

References 16 publications

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“…Waves are ubiquitous in the nocturnal boundary layer (Gossard and Hooke, 1975;Grivet-Talocia et al, 1999;Nappo, 2002;Rees et al, 2000) and can be generated by a number of mechanisms, including thunderstorms (Gedzelman, 1983), orographic excitation (terrain induced) (Chimonas, 1993), and shear instability (Emmanuel, 1973;Hooke et al, 1973). Ducted waves are bound between the ground surface and some atmospheric reflecting layer above or two reflecting critical layers aloft (Cooper et al, 2006;Fritts et al, 2003;Newsom and Banta, 2003;Rees and Mobbs, 1988), thus producing a wave guide allowing propagation to occur over long distances and time periods.…”

Section: Introductionmentioning

confidence: 99%

On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

Durden

Nappo²,

Leclerc

et al. 2013

Biogeosciences

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Abstract. The interpretation of flux measurements in nocturnal conditions is typically fraught with challenges. This paper reports on how the presence of wave-like disturbances in a time series, can lead to an overestimation of turbulence statistics, errors when calculating the stability parameter, erroneous estimation of the friction velocity u * used to screen flux data, and errors in turbulent flux calculations. Using time series of the pressure signal from a microbarograph, wavelike disturbances at an AmeriFlux site are identified. The wave-like disturbances are removed during the calculation of turbulence statistics and turbulent fluxes. Our findings suggest that filtering eddy-covariance data in the presence of wave-like events prevents both an overestimation of turbulence statistics and errors in turbulent flux calculations. Results show that large-amplitude wave-like events, events surpassing three standard deviations, occurred on 18 % of the nights considered in the present study. Remarkably, on flux towers located in a very stably stratified boundary-layer regime, the presence of a gravity wave can enhance turbulence statistics more than 50 %. In addition, the presence of the disturbance modulates the calculated turbulent fluxes of CO 2 resulting in erroneous turbulent flux calculations of the order of 10 % depending on averaging time and pressure perturbation threshold criteria. Furthermore, the friction velocity u * was affected by the presence of the wave, and in at least one case, a 10 % increase caused u * to exceed the arbitrary 0.25 m s −1 threshold used in many studies. This results in an unintended bias in the data selected for analysis in the flux calculations. The impact of different averaging periods was also examined and found to be variable specific. These early case study results provide an insight into errors introduced when calculating "purely" turbulent fluxes. These results could contribute to improving modeling efforts by providing more accurate inputs of both turbulent kinetic energy, and isolating the turbulent component of u * for flux selection in the stable nocturnal boundary layer.

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Section: Introductionmentioning

confidence: 99%

On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

Durden

Nappo²,

Leclerc

et al. 2013

Biogeosciences

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“…However, some computations can be shown, leading to values comparable with those presented by many authors (Emmanuel, 1973;Merrill, 1977, among others).…”

Section: An Evaluation Of the Local Richardson Numbermentioning

confidence: 71%

An interpolation method of randomly distributed atmospheric data in the height-time domain

Trombetti

Tampieri

1983

Boundary-Layer Meteorol

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A numerical method for objective interpolation of boundary-layer data in the height-time domain is presented. The method is based on a diffusive transport hypothesis and allows for the determination of the optima1 ratio between the height and time scales to be used for non-dimensionalising the independent variables z and t. This ratio, with dimensions of a velocity, may be related to the vertical transfer properties of the atmosphere. A few cases during springtime with different stability conditions are discussed, showing that this ratio varies by at least one order of magnitude between day and night.Nomenclature strength of the diffusive source in the numerical experiments diffusion height scale gravity acceleration height of the atmospheric layer examined Von Karman constant turbulent diffusion coefficient Monin-Obukhov length number of empirical data utilized to compute the value of a given quantity in the grid points total number of data points nondimensional distance between the grid point and the actual one, r = { Kt,,,, -t,ctuaJ/Atlz + Ggric, -~act,,&/W* 1 "' radius of influence gradient Richardson number, Ri = g/s[(a$/az)/(au/az)2] nondimensional ratio between height step AZ and height scale AZ values of s determined by the proposed method duration time of the numerical experiments or time range of the actual data initial time of the numerical experiments horizontal wind velocity friction velocity velocity defined as: u = Az/sAt 'exchange velocity', V = AZ/At = Az/SAt analytical 'exchange velocity', o, = 4K/D (Case A) or IJ, = a (Case B) weighting functions (see Equation (2)) roughness height diffusion parameter (see Equation (4)): K = az time step (arbitrarily chosen) height step (arbitrarily chosen) true height scale potential temperature diffusion time scale T = Dz/4K (Case A) or z = D/a (Case B) Boundary-Layer Meteorology 25 (1983) 159-170. OOOS-8314/83/0252-Ol59$01.80.

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“…We carried the microbarograph-sounder studies one step further at Haswell, Colorado, in the following autumn, by using not only a ground-based microbarograph array, but also a microbarograph atop the 150-m tower, in order to study gravity waves generated by shear instability in the planetary boundary layer. This type of wave generation had been studied earlier at Haswell, with results reported by Emnanuel et al (1972) and Emmanuel (1973). Together with a bivane anemometer atop the tower, the microbarograph provides direct data on the micro-scale wave phase velocity Vp (measured relative to the moving medium) given by the so-called impedance relation (Gossard and Munk, 1954) Ap V, -00 A Vx' (5) where Ap is the wave-associated pressure perturbation, A V x is the wave-associated horizontal velocity perturbation, and Q0 is the background atmospheric density.…”

Section: Sounder and Microbarograph Recordsmentioning

confidence: 74%

“…The facsimile records can then be used to select the events for analysis and to show what boundary-layer features are responsible for the differences in the turbulence intensity seen at the different instrument levels and times. This is the kind of approach used with great effect by Emmanuel et al (1973) and Bean et al (1973), for example.…”

Section: Gravity-wave Studiesmentioning

confidence: 95%

Acoustic echo-sounding techniques and their application to gravity-wave, turbulence, and stability studies

Beran

Hooke

Clifford

1973

Boundary-Layer Meteorol

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Abstract. This paper is a brief summary of recent experimental studies conducted by the WPL staff in order to: (a) compare acoustic echo strengths with those predicted from measured turbulence intensities and scatter theory; (b) develop optimum experimental geometries for Doppler work, and (c) use the acoustic echo-sounder as a quantitative tool in studies of gravity wave dynamics in, and immediately above, the stable planetary boundary layer. We find that the observed acoustic echo strengths are roughly an order of magnitude greater than those predicted theoretically. This discrepancy might be in part due to partial reflection although the comparison is somewhat clouded by uncertainties in our knowledge of the equipment characteristics, propagation losses, etc. Comparisons between Doppler and in situ wind measurements give confidence in the Doppler results, but further experimentation and comparisons are needed. Preliminary use of acoustic Doppler data in a case study of gravity-wave dynamics in the planetary boundary layer has yielded boundary-layer wind speed and direction profiles which give insight into the mechanisms responsible for the wave generation. The Doppler data yield estimates of the wave associated momentum fluxes (~ a few dyn cm -z) as well. The results derived from the acoustic techniques are quite encouraging, but thus far remain unsubstantiated by independent wind and flux measurements.

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Richardson number profiles through shear instability wave regions observed in the lower planetary boundary layer

Cited by 32 publications

References 16 publications

On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

On the impact of wave-like disturbances on turbulent fluxes and turbulence statistics in nighttime conditions: a case study

An interpolation method of randomly distributed atmospheric data in the height-time domain

Acoustic echo-sounding techniques and their application to gravity-wave, turbulence, and stability studies

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