Concurrency of Coherent Structures and Conditionally Sampled Daytime Sub-canopy Respiration

Zeeman, Matthias; Eugster, Werner; Thomas, Christoph

doi:10.1007/s10546-012-9745-2

Cited by 13 publications

(12 citation statements)

References 44 publications

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“…To study the cross‐wavelet power and relative phase in the time‐frequency space between the CO 2 concentration and flux with other climate elements, we analyzed their power spectra using the wavelet transform method. Today, this method has become a commonly used tool for the analysis of localized variations of power within a time series and has been used for numerous studies in geophysics (Allen & Smith, ; Farge, ; Grinsted et al, ; Howell & Mahrt, ; Katul & Parlange, ; Mahrt & Gibson, ; Morlet, ; Thomas & Foken, ; Torrence & Compo, ; Zeeman et al, ).…”

Section: Methodsmentioning

confidence: 99%

Characteristics of CO₂ Concentration and Flux in the Beijing Urban Area

Cheng

Liu

et al. 2018

JGR Atmospheres

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Since February 2012, CO2, H2O, and wind data at 10 Hz have been measured by the open‐path eddy covariance systems at 8, 16, 47, 80, 140, 200, and 280 m above ground level on the 325 m Beijing meteorological tower. Analysis of the data from 2013 to 2016 indicates that the annual averaged CO2 concentration increased and the local and regional CO2 emission decreased with the sequestration of background CO2 concentration. The maximum values occurred during winter, and the minimum values occurred during summer. During spring, summer, and autumn, there was a constant CO2 flux layer from 47 m to 140 m. However, during winter, CO2 flux increased with height, and the maximum appeared at approximately 140 m and then decreased with height. Above 47 m, the CO2 fluxes were represented as the net efflux, and below 16 m, the fluxes were near zero or a net uptake. At all observed heights, the diurnal variation in the CO2 concentration displayed a clear cycle with a peak corresponding to the morning transportation rush hour. The local wavelet power spectra of the CO2 concentration, CO2 flux, and other meteorological elements identified significant cross‐wavelet powers near the 24 h and 365 day bands for the CO2 concentration and flux with temperature, wind speed, friction velocity, and turbulent kinetic energy.

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Section: Methodsmentioning

confidence: 99%

Characteristics of CO₂ Concentration and Flux in the Beijing Urban Area

Cheng

Liu

et al. 2018

JGR Atmospheres

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“…Both, the mixed-layer rolls and the streaks, can be linked to microfronts, which can be observed in sweep-and-ejection patterns or ramp-like patterns in the time series of wind velocity, temperature, and humidity (e.g. Barthlott et al 2007;Fresquet et al 2009;Zhang et al 2010;Takimoto et al 2013;Zeeman et al 2013).…”

Section: Introductionmentioning

confidence: 99%

“…Barthlott et al 2007;Zhang et al 2010;Segalini and Alfredsson 2012;Zeeman et al 2013). The sweep-and-ejection viewpoint of coherent structures in meteorology is determined by this technique.…”

Section: Introductionmentioning

confidence: 99%

Turbulent Structures and Coherence in the Atmospheric Surface Layer

Träumner

Damian

Stawiarski

et al. 2014

Boundary-Layer Meteorol

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Organized structures in turbulent flow fields are a well-known and still fascinating phenomenon. Although these so-called coherent structures are obvious from visual inspection, quantitative assessment is a challenge and many aspects e.g., formation mechanisms and contribution to turbulent fluxes, are discussed controversially. During the "High Definition Clouds and Precipitation for Advancing Climate Prediction" Observational Prototype Experiment (HOPE) from April to May 2013, an advanced dual Doppler lidar technique was used to image the horizontal wind field near the surface for approximately 300 h. A visual inspection method, as well as a two-dimensional integral length scale analysis, were performed to characterize the observations qualitatively and quantitatively. During situations with forcing due to shear, the wind fields showed characteristic patterns in the form of clearly bordered, elongated areas of enhanced or reduced wind speed, which can be associated with near-surface streaks. During calm situations with strong buoyancy forcing, open cell patterns in the horizontal divergence field were observed. The measurement technique used enables the calculation of integral length scales of both horizontal wind components in the streamwise and cross-stream directions. The individual length scales varied considerably during the observation period but were on average shorter during situations with z/L < 0 compared to strongly stable situations. During unstable situations, which were dominated by wind fields with structures, the streamwise length scales increased with increasing wind speed, whereas the cross-stream length scales decreased. Consequently, the anisotropy increased from 1 for calm situations to values of 2-3 for wind speeds of 8-10 m s −1 . During neutral to stable situations, the eddies were on average quite isotropic in the horizontal plane.

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“…Wavelet analyses have been widely used to extract coherent structures from temperature, wind field and humidity fluctuation time series (Collineau and Brunet 1993a, b;Thomas and Foken 2007;Zhang et al 2011;Zeeman et al 2013). A wavelet is a localized function ϕ((t − b)a −1 ) in time (or space) t which is scaled with a factor a and shifted to the position b.…”

Section: Wavelet Analysismentioning

confidence: 99%

Assessment of Surface-Layer Coherent Structure Detection in Dual-Doppler Lidar Data Based on Virtual Measurements

Stawiarski

Träumner

Kottmeier

et al. 2015

Boundary-Layer Meteorol

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Dual-Doppler lidar has become a useful tool to investigate the wind-field structure in two-dimensional planes. However, lidar pulse width and scan duration entail significant and complex averaging in the resulting retrieved wind-field components. The effects of these processes on the wind-field structure remain difficult to investigate with in situ measurements. Based on high resolution large-eddy simulation (LES) data for the surface layer, we performed virtual dual-Doppler lidar measurements and two-dimensional data retrievals. Applying common techniques (integral length scale computation, wavelet analysis, twodimensional clustering of low-speed streaks) to detect and quantify the length scales of the occurring coherent structures in both the LES and the virtual lidar wind fields, we found that, (i) dual-Doppler lidar measurements overestimate the correlation length due to inherent averaging processes, (ii) the wavelet analysis of lidar data produces reliable results, provided the length scales exceed a lower threshold as a function of the lidar resolution, and (iii) the low-speed streak clusters are too small to be detected directly by the dual-Doppler lidar. Furthermore, we developed and tested a method to correct the integral scale overestimation that, in addition to the dual-Doppler lidar, only requires high-resolution wind-speed variance measurements, e.g. at a tower or energy balance station.

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Concurrency of Coherent Structures and Conditionally Sampled Daytime Sub-canopy Respiration

Cited by 13 publications

References 44 publications

Characteristics of CO₂ Concentration and Flux in the Beijing Urban Area

Characteristics of CO₂ Concentration and Flux in the Beijing Urban Area

Turbulent Structures and Coherence in the Atmospheric Surface Layer

Assessment of Surface-Layer Coherent Structure Detection in Dual-Doppler Lidar Data Based on Virtual Measurements

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Concurrency of Coherent Structures and Conditionally Sampled Daytime Sub-canopy Respiration

Cited by 13 publications

References 44 publications

Characteristics of CO2 Concentration and Flux in the Beijing Urban Area

Characteristics of CO2 Concentration and Flux in the Beijing Urban Area

Turbulent Structures and Coherence in the Atmospheric Surface Layer

Assessment of Surface-Layer Coherent Structure Detection in Dual-Doppler Lidar Data Based on Virtual Measurements

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Characteristics of CO₂ Concentration and Flux in the Beijing Urban Area

Characteristics of CO₂ Concentration and Flux in the Beijing Urban Area