Page 170 - 《高原气象》2026年第2期

高 原 气 象 45 卷
470

A Study on Flux Contributions of Turbulent Coherent Structures over

Forest Underlying Surfaces Using the CEEMD Method

WANG Yanqi， ZHANG Yu， SU Youqi， ZHANG Qian， YE min
（College of Atmospheric Sciences， Chengdu University of Information Technology /Chengdu Plain Urban Meteorology and
Environment Sichuan Provincial Field Scientific Observation and Research Station， Chengdu 610225， Sichuan， China）

Abstract： In order to study the turbulent coherent structure characteristics under the complex underlying surface
of forests， three-layer turbulence data set up at 1. 33 times， 2. 53 times， and 3. 86 times canopy degrees in the ar‐
tificial forest area of Mount Si E in Leshan City， Sichuan Province （canopy height of 15 m） in May 2021 were
used to observe the turbulent characteristics of the rough sublayer， rough sublayer， and constant flux layer
boundaries， as well as the constant flux layer. Based on the observation data mentioned above， three coherent
structural modes of different scales at different heights were extracted using the Complementary Empirical Mode
Decomposition （CEEMD） algorithm. The flux contribution of coherent structures was quantified， and 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 scales， and the modes exhibit typical coherence. In terms
of the contribution of coherent structures to flux， there are differences at different heights. The flux contributions
to sensible heat， latent heat， and momentum are 21%， 17%， and 11% at 20 m， 13%， 11%， and 7% at 38 m，
and 12%， 10%， and 6% at 56 m， respectively. This indicates that at three heights， the transport efficiency of sca‐
lar fluxes such as sensible and latent heat flux by coherent structures is greater than that of momentum flux， and
the flux contribution of coherent structures is the largest on the 20 m rough sublayer， which 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 conditions， followed by stable and unstable
conditions. For latent heat flux， the maximum flux contribution occurs under stable conditions at all three
heights， followed 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 heights （38 m and 56 m）， while the
cleaning process plays a dominant role as the observation height decreases to approach the rough sub layer. Final‐
ly， the relationship between the slope strength， stability parameters， and friction velocity of coherent structural
structures was studied. For both horizontal and vertical wind， the slope strength of both increases with the in‐
crease of friction velocity， but 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 surfaces， and supports the subsequent study of turbulent structures.
Key words： turbulence； forest underlying surface； coherent structures； flux contribution