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Gembloux Agro-Bio Tech (GxABT)
Gembloux Agro-Bio Tech (GxABT)
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Analysis of turbulent fluxes with the means of the continuous wavelet transform on the Belgian ICOS sites of Lonzée and Vielsalm

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Tzvetkov, Diana ULiège
Promotor(s) : Heinesch, Bernard ULiège ; Charles, Catherine ULiège
Date of defense : 30-Aug-2023 • Permalink : http://hdl.handle.net/2268.2/18257
Details
Title : Analysis of turbulent fluxes with the means of the continuous wavelet transform on the Belgian ICOS sites of Lonzée and Vielsalm
Translated title : [fr] Analyse des flux turbulents avec la transformation en ondelettes continue sur les sites belges d'ICOS de Lonzée et Vielsalm
Author : Tzvetkov, Diana ULiège
Date of defense  : 30-Aug-2023
Advisor(s) : Heinesch, Bernard ULiège
Charles, Catherine ULiège
Committee's member(s) : Mercatoris, Benoît ULiège
Bitton, Jonathan ULiège
Munhoven, Guy ULiège
Schaller, Carsten 
Language : English
Number of pages : 67
Keywords : [en] turbulent fluxes
[en] wavelet analysis
[en] mesoscale motions
Discipline(s) : Physical, chemical, mathematical & earth Sciences > Physics
Research unit : Biosystems Dynamics and Exchanges (Biodyne), Gembloux Agro-Bio Tech
Target public : Researchers
Student
Institution(s) : Université de Liège, Liège, Belgique
Degree: Master en bioingénieur : sciences et technologies de l'environnement, à finalité spécialisée
Faculty: Master thesis of the Gembloux Agro-Bio Tech (GxABT)

Abstract

[fr] The eddy covariance and Fourier decomposition are the standard methods for the calculation and analysis of the turbulent flux. Nonetheless, their applicability is restricted by the necessity of steady- state flow conditions, rendering them unsuitable for analyzing mesoscale motions, which are the most prominent cause for energy balance unclosure according to recent review papers. Consequently, the wavelet transform has gained traction for turbulent flux analysis in the past few years. Originally developed for signal analysis, this tool effectively captures non-stationary power by decomposing the signal in both the temporal and frequency domains, and it can be used to derive flux cospectra and calculate the turbulent flux. The present paper makes use of this tool in the scope of two research objectives.
First, the parameters of the wavelet covariance formula are adapted to establish equivalence between wavelet and eddy covariance are equivalent for stationary half-hour records. Through a sensitivity analysis, the influence of parameters such as padding (introducing artificial values at signal boundaries), the shortest analyzed period, the scale step (δ j), the threshold for the cone of influence (qcoi) in covariance computation are explored, along with the choice of mother wavelet and normalization. The second research objective aims at investigating components of the turbulent flux that oscillate in periods larger than 30 min on two ICOS sites, namely Lonzée and Vielsalm, and that could explain energy balance unclosure on these sites.To achieve this, CO2, H2O, and temperature measurements are utilized to derive wavelet flux cross-scalograms, cospectra and ogives. These different representations revealed the presence of flux components in the low-frequency range that are much important that the energy balance residuals, which suggests that the flux aggregated over 3.2 hours is overestimated, as a consequence of a too short averaging time or as the consequence of biased observations of quasi-stationary motions. In the conditions of mean wind and with the nature and scale of heterogeneities on Lonzée and Vielsalm, the presence of quasi-stationary motions is possible but could not be ascertained.


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Author

  • Tzvetkov, Diana ULiège Université de Liège > Gembloux Agro-Bio Tech

Promotor(s)

Committee's member(s)

  • Mercatoris, Benoît ULiège Université de Liège - ULiège > Département GxABT > Biosystems Dynamics and Exchanges
    ORBi View his publications on ORBi
  • Bitton, Jonathan ULiège Université de Liège - ULiège >
    ORBi View his publications on ORBi
  • Munhoven, Guy ULiège Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Labo de physique atmosphérique et planétaire (LPAP)
    ORBi View his publications on ORBi
  • Schaller, Carsten University of Münster
  • Total number of views 58
  • Total number of downloads 39










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