Climatology of Biomass Smoke in Wildland Areas of the United States

With the increasing use of prescribed fire, predicting the potential impacts are becoming more and more important. Of great concern are the effects of smoke on human health and visibility. To help land managers anticipate and plan for potential trajectories and dispersion of biomass smoke in the lower atmosphere, we are developing a climate data base of surface wind and mixing height. The data base will cover the entire United States, including Alaska and Hawaii, at 5 km spatial resolution with selected domains to 30 meter spatial resolution.

To generate surface winds, we experimented with a number of numerical methods including fully physical 3-dimensional meteorological models (MM5), hydrostatic flow models (MESMOD, WINFLO), conservation-of-mass models (NUATMOS, CALMET), and statistical approaches. We have found that simple one-level hydrostatic flow models, which use upper-air data (from the NCEP Reanalysis package) to solve equations of motion around complex topography, can accurately simulate prevailing surface winds to about 5 km spatial resolution. Because of its simplicity, this type of model can be run at very high speeds. This allows the formation of a 40-year record of twice daily wind. In this way, managers can determine the potential frequency of wind speed and direction during the morning (12Z) or afternoon (00Z) on any given day of the year. In addition, we have coupled the flow model to a 3-dimensional conservation-of-mass model to simulate surface winds at about 30 meter spatial resolution. This will allow the generation of wind statistics at very fine resolution for small domains within critical regions.

It is assumed that afternoon mixing heights are controlled by the synoptic weather pattern, while morning mixing heights are a function of local topography. For this reason, afternoon mixing heights are determined from radiosonde observation data, building on data sets that have been previously generated. Morning mixing heights are determined from the synoptic conditions coupled to an algorithm that estimates the strength and depth of inversions from the shape and size of the basin or valley. GIS tools in ArcInfo Grid are used to analyze the terrain and develop spatial displays of local inversion potential.

The product of surface wind and mixing height often are used as an index of ventilation potential. Some examples are given that show application of the index and climate statistics to smoke management problems.