The Turbulent Pressure Spectrum Within the Roughness Sublayer of a Subarctic Forest Canopy

The turbulent static pressure spectrum (Formula presented.) as a function of longitudinal wavenumber (Formula presented.) in the roughness sublayer of forested canopies is of interest to a plethora of problems such as pressure transport in the turbulent kinetic energy budget, pressure pumping from snow or forest floor, and coupling between flow within and above canopies. Long term static pressure measurements above a sub-arctic forested canopy for near-neutral conditions during the winter and spring were collected and analyzed for three snow cover conditions: trees and ground covered with snow, trees are snow free but the ground is covered with snow, and snow free cover. In all three cases, it is shown that (Formula presented.) obeys the attached eddy hypothesis at low wavenumbers (Formula presented.) —with (Formula presented.) and Kolmogorov scaling in the inertial subrange at higher wavenumbers—with (Formula presented.), where (Formula presented.) is the friction velocity at the canopy top, (Formula presented.) is the mean turbulent kinetic energy dissipation rate, (Formula presented.) is the distance from the snow top, and (Formula presented.) is the boundary layer depth. The implications of these two scaling laws to the normalized root-mean squared pressure (Formula presented.) and its newly proposed logarithmic scaling with normalized wall-normal distance (Formula presented.) are discussed for snow covered and snow free vegetation conditions. The work here also shows that the (Formula presented.) in the (Formula presented.) appears more extensive and robust than its longitudinal velocity counterpart.

Duke Scholars

Author Gabriel G. Katul Civil and Environmental Engineering