Page 161 - 《高原气象》2025年第3期

3 期 丁 一等：川南森林冠层上方动量和标量的湍流输送效率 719

Turbulent Transport Efficiency of Momentum and Sscalar

over Forest Canopy in Southern Sichuan

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DING Yi ， ZHANG Yu ， FAN Demin ， SU Youqi ， ZHANG Qian ， WANG Yanqi ， WANG Yanqi 1
（1. 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；
2. Anhui Wuhu Wanzhi District Meteorological Bureau， Wuhu 241100， Anhui， China；
3. Sichuan Chongzhou Meteorological Bureau， Chongzhou 611230， Sichuan， China；
4. Sichuan Deyang Meteorological Bureau， Deyang 618000， Sichuan， China）
Abstract： The turbulent transport characteristics of momentum and scalar over the canopy were studied by using
the three levels （20 m， 38 m and 56 m） turbulence data measured at the 60m forest micro meteorological tower
in southern Sichuan from May 1 to June 30， 2021. Coherent structure is the main form of turbulent motion，
which is composed of updraft （ejection） and downdraft （sweep）. In this paper， the quadrant analysis method is
used to analyze the boundary of the roughness sublayer， roughness sublayer and constant flux layer above the for‐
est canopy and the ejection-sweep motion characteristics of the constant flux layer， including the difference of
ejection and sweep contribution to flux， the difference between momentum and scalar transport， and the differ‐
ence between different scalar （T， q， CO） transport. The results show that under unstable and stable conditions，
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the ejection dominates the scalar transport at all three levels， while the sweep is the main eddy current motion for
scalar transport above the roughness sublayer under neutral conditions. For the momentum flux， under unstable
conditions， the ejection dominates at all three levels. Under stable conditions， the ejection dominates at the
roughness sublayer and the constant flux layer， while at the boundary of the roughness sublayer and the constant
flux layer， the effect of the sweep is greater than that of the ejection. Under neutral conditions， the flux contribu‐
tion of the sweep is greater than that of the ejection except for the roughness sublayer. The third-order cumulant
expansion method （CEM） can more accurately express the flux contribution caused by ejection and sweep，
while the incomplete cumulant expansion method （ICEM） is poor in simulating the temperature at the boundary
of roughness sublayer and constant flux layer. Through the calculation of transmission efficiency， the difference
between momentum and scalar transmission is further quantified. The turbulent transfer efficiency of momentum
decreases with increasing instability， while the heat transfer efficiency is the opposite. Atmospheric stability is an
important factor controlling momentum and scalar transfer， and the transfer efficiency of water vapor is less af‐
fected by atmospheric stability. Under the condition of strong instability， the heat transfer efficiency is more ef‐
fective than other scalar transfer.
Key words： quadrant analysis； ejection-sweep； transport efficiencies； forest canopy