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.