Mean and turbulent flows in and above a forest canopy during a prescribed burn event in the New Jersey Pine Barrens: observations and simulations using ARPS-CANOPY

In this study, mean and turbulence fields inside a forest canopy during a prescribed burn event in the New Jersey Pine Barrens are simulated using a modified version of the Advanced Regional Prediction System (ARPS) model containing a canopy sub-model (ARPS-CANOPY). A 3D high resolution plant area density dataset is utilized to define the characteristics of the canopy and the low-intensity prescribed fire is represented in the model as a heat source. The simulated profiles of mean wind, temperature and turbulent kinetic energy are compared to observations made by a 20 m and a 30 m flux tower during both the pre-burn phase of the experiment and the period of time when the flux towers experienced perturbed conditions due to the impinging fire. The ARPS-CANOPY model reproduces the characteristics of the tower observations. The shapes of the simulated mean and turbulent flows are in good agreement with the tower observations, although TKE is underestimated and the mean winds are too weak (too strong) below (above) canopy top. The characteristics and source of turbulence in and around the fire line are examined. Considerable variability in the mean TKE both spatially and temporally is noted, and it is concluded that buoyancy is the dominant turbulence generator throughout the modeling domain with shear generation playing a secondary role away from the immediate fire line. These findings have implications for predictions of smoke from low-intensity fires since the transport of smoke from low-intensity fires can be sensitive to near surface meteorological conditions and, in particularly, turbulent flows.