Tuesday, 18 November 2003: 11:00 AM
Using a simple parcel model to investigate the Haines Index
We present a simple parcel model, a one dimensional cloud parcel model, that features entrainment, conversion of cloud condensation to rain drops, cloud water and rain water drag, and downdraft evaporative cooling. The simple parcel model is used to describe the ascent and descent of air parcels originating from a surface fire for approximately 176 different near--surface environmental humidity and stability profiles. We present the results from these environmental profiles for three different parcel model configurations. The first is the parcel model with the following features excluded: entrainment, conversion of cloud water to rain water, drag, and downdraft evaporative cooling. The second is the parcel model with all the features included. The third is the parcel model with all features included but a shallow upper--level inversion layer is inserted into the environmental profile. In each case we examine the average properties of discrete buoyant wildfire parcels, or thermals, for moisture and stability conditions that correspond to the Haines Index for low to high potential for severe fire development. The results of the parcel model allow us to examine the properties of fire thermals and their sensitivity to near--surface environmental temperature and humidity lapse rates, and a different vertical structure of the atmosphere, and in the process explore the correspondence between atmospheric stability and moisture, and fire thermal properties, and the Haines Index. This presentation will show that a simple parcel model can provide a quick, simple, yet fundamental, evaluation of the Haines Index.
Supplementary URL: http://ftp://ftp.met.utah.edu/pub/mjenkins/5sym/