A Study on Flux Contributions of Turbulent Coherent Structures over Forest Underlying Surfaces Using the CEEMD Method

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  • College of Atmospheric SciencesChengdu University of Information Technology /Chengdu Plain Urban Meteorology and
    Environment Sichuan Provincial Field Scientific Observation and Research Station
    Chengdu 610225SichuanChina

Online published: 2026-01-28

Abstract

In order to study the turbulent coherent structure characteristics under the complex underlying surface of foreststhree-layer turbulence data set up at 1. 33 times2. 53 timesand 3. 86 times canopy degrees in the ar‐ tificial forest area of Mount Si E in Leshan CitySichuan Provincecanopy height of 15 min May 2021 were used to observe the turbulent characteristics of the rough sublayerrough sublayerand constant flux layer boundariesas well as the constant flux layer. Based on the observation data mentioned abovethree coherent structural modes of different scales at different heights were extracted using the Complementary Empirical Mode DecompositionCEEMDalgorithm. The flux contribution of coherent structures was quantifiedand the main feature quantities of coherent structures were analyzed and studied. The results indicate that the CEEMD algo‐ rithm can extract coherent structural modes of different scalesand the modes exhibit typical coherence. In terms of the contribution of coherent structures to fluxthere are differences at different heights. The flux contributions to sensible heatlatent heatand momentum are 21%17%and 11% at 20 m13%11%and 7% at 38 mand 12%10%and 6% at 56 mrespectively. This indicates that at three heightsthe transport efficiency of sca‐ lar fluxes such as sensible and latent heat flux by coherent structures is greater than that of momentum fluxand the flux contribution of coherent structures is the largest on the 20 m rough sublayerwhich decreases with in‐ creasing observation height. The contribution of coherent structures to flux varies with different flux types and layer types under different stable layer structures. The maximum flux contribution of coherent structures to the transport of sensible heat flux at three heights occurs under neutral conditionsfollowed by stable and unstable conditions. For latent heat fluxthe maximum flux contribution occurs under stable conditions at all three heightsfollowed by neutral and unstable conditions. The results of the flux contribution to the cleaning and spraying processes indicate that the spraying process dominates at higher heights38 m and 56 m),while the cleaning process plays a dominant role as the observation height decreases to approach the rough sub layer. Final‐ lythe relationship between the slope strengthstability parametersand friction velocity of coherent structural structures was studied. For both horizontal and vertical windthe slope strength of both increases with the in‐ crease of friction velocitybut there are differences in the performance of stability parameters. The slope strength of horizontal wind is maximum under neutral conditions and decreases with the increase of stability and instabili‐ ty. The slope strength of the vertical wind is maximum under unstable conditions and decreases with the increase of stability as the coherent vertical motion is suppressed. The research conclusion of this article provides a statisti‐ cal understanding of the flux contribution and coherent motion characteristics of coherent structures under com‐ plex underlying surfacesand supports the subsequent study of turbulent structures.

Cite this article

WANG Yanqi, ZHANG Yu, SU Youqi, ZHANG Qian, YE min . A Study on Flux Contributions of Turbulent Coherent Structures over Forest Underlying Surfaces Using the CEEMD Method[J]. Plateau Meteorology, 0 : 1 . DOI: 10.7522/j.issn.1000-0534.2025.00080

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