Characterization of Coherent structures in the Atmospheric Surface Layer

Krusche, Nísia; Oliveira, Amauri Pereira de

doi:10.1023/a:1026096805679

Cited by 33 publications

(30 citation statements)

References 23 publications

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“…They found that coherent structures contribute ''heavily'' to observed fluxes, but they also stated that subjectivity in choosing threshold durations causes differences in quantitative estimates of the structure contributions. A recent publication by Krusche and Oliveira (2004) found the intermittency function to best identify temperature ramps, followed by the Mexican hat wavelet transform in a 43 hours data set. A remarkable conclusion of their work is that, after applying a statistical test, the results of the two methods do not belong to the same population.…”

Section: Other Conceptsmentioning

confidence: 99%

Detection and analysis of coherent structures in urban turbulence

Feigenwinter

Vogt

2005

Theor. Appl. Climatol.

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SummaryThe continuous wavelet transform provides a suitable tool to visualize the vertical structure of turbulence and to detect coherent structures in turbulent time series. This is demonstrated with a simple example of an artificially ramp structured time series. In this study turbulence data, i. , sampled with 20.83 Hz and measured simultaneously at three levels (z=h ¼ 1.5, 2.1 and 3.2, with z as the sensor height and h the height of the roughness elements) over an urban canopy in the inner city of Basel, Switzerland, are analyzed. The detection of the coherent structures was performed using the Mexican hat wavelet and the zero-crossing method. The analysis for unstable conditions shows that organized structures (ejection-sweep cycles) cover about 45% of the total run time. A conditional average from a total of 116 detected ejection-sweep sequences during 7 hours was calculated over a time window of 100 seconds. This dominating time scale was derived from peak frequencies of the wavelet spectra as well as from the Fourier spectra. It is shown that the normalized amplitudes of fluctuations of temperature and longitudinal wind speed during the events are largest at the lowest measurement level just above the canopy and decrease with increasing distance from the roughness elements. A comparison of related studies over different non-urban surfaces (mainly forests) shows that the shape of conditionally averaged ejectionsweep sequences is very similar for all canopies, however, the dominating time scale in general increases the rougher the surface is and the higher the roughness elements are.

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Section: Other Conceptsmentioning

confidence: 99%

Detection and analysis of coherent structures in urban turbulence

Feigenwinter

Vogt

2005

Theor. Appl. Climatol.

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“…Several methods of identification of single events in time series of wind velocity or scalars exist, such as the variable interval time average (VITA), intermittency function or wavelet analysis (Gao et al, 1992;Krusche and De Oliveira, 2004;Thomas and Foken, 2005). Krusche and De Oliveira (2004) tested different wavelet functions for the detection method and found that the average event duration was 24-38 s. Thomas and Foken (2005) used wavelet analysis and found that the peaks associated with event duration in time series of air temperature ranged from 14 to 120 s. We tested the events' duration by calculating the wavelet spectra for time series of vertical velocity and air temperature for both campaigns (not shown). The peak in the wavelet spectra for vertical velocity was located at ∼25 s; for air temperature, the highest contributions occurred from 60 to 100 s.…”

Section: Resultsmentioning

confidence: 99%

“…This is obtained by using wavelet functions that are finite in time, as opposed to the infinite sines and cosines used in the Fourier analysis. This tool has been used in many geophysical studies and it is especially useful in the analysis of the turbulent motions over plant canopies, which are not always periodic and stationary (Farge, 1992;Collineau and Brunet, 1993b;Turner et al, 1994;Terradellas et al, 2001;Krusche and De Oliveira, 2004;Bolzan and Vieira, 2006). In this work, a package of Matlab scripts called Wavelab 2 was used to decompose the time series using orthogonal wavelets.…”

Section: Methodsmentioning

confidence: 99%

Scale dependence of coherent structures' contribution to the daytime buoyancy heat flux over the Pantanal wetland, Brazil

Zeri

Sá

2011

Atmospheric Science Letters

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The contribution of organized motions to buoyancy heat flux was determined for several time scales by applying wavelet decomposition to signals of vertical velocity and air temperature. Measurements were performed using an eddy covariance system installed over the Pantanal wetland, in Brazil, during two campaigns (1998 and 1999). The signals were decomposed in several time scales and then used in the quadrant analysis. Overall, coherent structures were responsible for ∼40% of the buoyancy heat flux, if the contributions of ejections and sweeps are summed over the range of 10-100 s, which excludes the contribution of stochastic high-frequency turbulence and low-frequency mesoscale motions.

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“…It has been pointed out that coherent structures detected in humidity time series above forests or fields can be very important since they potentially control the mass exchange between the lower and upper layers (Krusche and De Oliveira, 2004). Coherent structures in humidity time series were not examined here since the vegetation cover was rather low.…”

Section: Discussionmentioning

confidence: 99%

“…A variety of conditional sampling techniques have been developed in order to objectively identify structural shapes in meteorological time series, and often contradictory interpretations of results obtained with different methods are reported (Krusche and De Oliveira, 2004, and references therein). Recently, Belušić and Mahrt (2012) introduced a simple linear technique to extract geometrical shapes that are usually observed in small scale turbulence and in meso-scale flows.…”

Section: Introductionmentioning

confidence: 99%

Studying geometric structures in meso-scale flows

Halios

Helmis

Asimakopoulos

2014

Front. Environ. Sci.

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Geometric shapes of coherent structures such as ramp or cliff like signals, step changes and waves, are commonly observed in meteorological temporal series and dominate the turbulent energy and mass exchange between the atmospheric surface layer and the layers above, and also relate with low-dimensional chaotic systems. In this work a simple linear technique to extract geometrical shapes has been applied at a dataset which was obtained at a location experiencing a number of different mesoscale modes. It was found that the temperature field appears much better organized than the wind field, and that cliff-ramp structures are dominant in the temperature time series. The occurrence of structural shapes was related with the dominant flow patterns and the status of the flow field. Temperature positive cliff-ramps and ramp-cliffs appear mainly during night time and under weak flow field, while temperature step and sine structures do not show a clear preference for the period of day, flow or temperature pattern. Uniformly stable, weak flow conditions dominate across all the wind speed structures. A detailed analysis of the flow field during two case studies revealed that structural shapes might be part of larger flow structures, such as a sea-breeze front or down-slope winds. During stagnant conditions structural shapes that were associated with deceleration of the flow were observed, whilst during ventilation conditions shapes related with the acceleration of the flow.

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Characterization of Coherent structures in the Atmospheric Surface Layer

Cited by 33 publications

References 23 publications

Detection and analysis of coherent structures in urban turbulence

Detection and analysis of coherent structures in urban turbulence

Scale dependence of coherent structures' contribution to the daytime buoyancy heat flux over the Pantanal wetland, Brazil

Studying geometric structures in meso-scale flows

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