A SIMULATION OF THE CANOPY MICROENVIRONMENT USING HIGHER ORDER CLOSURE PRINCIPLES (NUMERICAL, CROPS, MICROMETEOROLOGY)

TILDEN PAYNE MEYERS, Purdue University

Abstract

The deficiencies of gradient diffusion theory to model turbulent transport in the plant canopy are becoming widely recognized although both modeling and experimental efforts still rely heavily upon these concepts. Recently, second order closure models have been used to successfully simulate the profiles of the mean wind speed, tangential stress and turbulent kinetic energy within a canopy. Problems with parameterizing the third order transport term for the tangential stress have been noted. In addition, second order closure models have only been applied to a few types of canopy structures and further testing is needed. A third order closure model has been developed to simulate airflow in a vegetative canopy for neutral conditions. The model contains simplified equations for the third order terms, bypassing the need to parameterize them as is done in second order closure. The model has been applied to a maize, soybean, wheat, orange, bean and sitka spruce canopy. The simulated mean wind profiles compared favorably with measurements. The model also produced a reversal of the wind shear for the orange, maize and spruce canopies. This feature of canopy flow cannot be predicted with gradient diffusion models. The third order model established the framework for a more complete and realistic model of the canopy microenvironment. Equations for heat and moisture fluxes have been included and coupled to a leaf energy balance equation. A detailed canopy radiation model determined the net radiant fluxes at each level in the canopy. The root mean square errors for the temperature and mixing ratio profiles were less than 0.41(DEGREES)C and 0.45 gm H(,2)O/kg air, respectively, for all cases examined. The buoyant effects on the temperature, humidity and wind profiles were negligible although the sensible heat flux exceeded 200 W m('-2). The transport terms in the heat, moisture and momentum budgets were very important within the canopy but negligible above the canopy.

Degree

Ph.D.

Subject Area

Atmosphere

COinS