Local flux-profile relationships of wind speed and temperature in a canopy layer in atmospheric stable conditions

[摘要] The particularities of the physics of the canopy layer pose challenges to thedetermination and use of traditional universal functions so helpful in theatmospheric surface layer. Progress toward "universal-like functions" such asthose provided by Monin-Obukhov similarity theory for the canopy layer hasbeen modest. One of the challenges lies in that the assumptions underlyingMonin-Obukhov similarity theory do not hold within a canopy layer. This paperthus examines the local flux-profile relations for wind (Φ_m) and fortemperature (Φ_h). It uses three different stability parameters, i.e.,h/L(h) at tree top, local z/L(z), and the local bulkRichardson number (Ri), within a tall forest canopy in nighttimestable (indicated by h/L(h) > 0) conditions. Results suggestthat the in-canopy Φ_m can be described using the local Richardsonnumber Ri. Furthermore, Φ_m is found to increase linearlywith Ri in the upper canopy layer for |Ri| < 1. When local |Ri| > 1, |Φ_m|decreases with |Ri| in a power function, a result consistent for alllevels of measurements within the canopy. When both local Φ_h andlocal Ri are positive, i.e., the local downward turbulent heat fluxis consistent with the local temperature gradient, the local Φ_hincreases with the local Ri when Ri < 1. However,Φ_h does not change with Ri (or much more scattered) whenRi > 1. The relationship between local Φ_h andRi disappears when counter-gradient heat transfer occurs in stronglystable conditions. A self-correlation analysis is used to examine theinfluence of self-correlation and the physical meaning of theserelationships.

[学科分类] 地球化学与岩石