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A Physics‐Based Universal Indicator for Vertical Decoupling and Mixing Across Canopies Architectures and Dynamic Stabilities
Author(s) -
Peltola O.,
Lapo K.,
Thomas C. K.
Publication year - 2021
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl091615
Subject(s) - canopy , environmental science , buoyancy , drag , terrain , eddy covariance , decoupling (probability) , turbulence , atmospheric sciences , drag coefficient , stratification (seeds) , ecosystem , meteorology , computational fluid dynamics , mechanics , geology , ecology , physics , dormancy , seed dormancy , germination , botany , control engineering , engineering , biology
Air flows may be decoupled from the underlying surface either due to strong stratification of air or due to canopy drag suppressing cross‐canopy mixing. During decoupling, turbulent fluxes vary with height and hence identification of decoupled periods is crucial for the estimation of surface fluxes with the eddy covariance (EC) technique and computation of ecosystem‐scale carbon, heat, and water budgets. A new indicator for identifying the decoupled periods is derived using forces (buoyancy and canopy drag) hindering movement of a downward propagating air parcel. This approach improves over the existing methods since (1) changes in forces hindering the coupling are accounted for, and (2) it is based on first principles and not on ad hoc empirical correlations. The applicability of the method is demonstrated at two contrasting EC sites (flat open terrain, boreal forest) and should be applicable also at other EC sites above diverse ecosystems (from grasslands to dense forests).