Nocturnal boundary layer turbulence over a tree canopy

Date of Completion

January 1999

Keywords

Physics, Atmospheric Science|Engineering, Environmental

Degree

Ph.D.

Abstract

This dissertation is a compilation of studies that probe into many facets of nocturnal boundary layer (NBL) turbulence over tree canopies. Primarily, these studies focused on investigations into scales of NBL motions, stability classification, vertical dispersion and kinematic flux calculations. The chapters present: (1) a NBL wind component signal analysis where fast response data were used to determine the resolution of NBL turbulence, (2) a NBL vertical dispersion study where a lidar system was used to measure plume growth over a deciduous forest in the NBL, and (3) a new method for rotating NBL three-dimensional wind data measurements. The main work was prompted by questions raised by earlier studies that are included in the appendices. ^ The main conclusions of this research were: (1) a sampling rate of 50 Hz is required to capture an unbiased NBL turbulence signal, (2) a gradient based stability parameter offers a more precise description of stability in the NBL due to the low levels of turbulence present, (3) the ergodic condition, which assumes that time and space averages are equal, was found to be met in the NBL above a tree canopy as demonstrated by a consistent prediction of vertical dispersion to actual dispersion as measured with a lidar system, and (4) a frequency-weighted technique was developed to reduce flow intermittency effects that skew NBL calculations using the traditional rotation techniques. ^

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