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Main Collaborators: Janice Coen, NCAR Morwenna Griffiths,Monash Mary Ann Jenkins,York Don Latham, USFS Don Middleton,NC PowerPoint Presentation
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Coupled Fire-Atmosphere Research Observations and Modeling. by Terry L. Clark/UBC. Main Collaborators: Janice Coen, NCAR Morwenna Griffiths,Monash Mary Ann Jenkins,York Don Latham, USFS Don Middleton,NCAR David Packham, BoM Larry Radke,NCAR/RI Michael Reeder,Monash Roland Stull, UBC.

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Coupled Fire-Atmosphere Research

Observations and Modeling


Terry L. Clark/UBC

Main Collaborators:

Janice Coen, NCAR

Morwenna Griffiths,Monash

Mary Ann Jenkins,York

Don Latham, USFS

Don Middleton,NCAR

David Packham, BoM

Larry Radke,NCAR/RI

Michael Reeder,Monash

Roland Stull, UBC

  • Observations using IR Imagery
    • -overview of IR camera and analysis techniques
    • -some prescribed and wild fire field experiments
  • Model
    • -Description of dynamic code
    • -Description of early NCAR fire code
      • -some results
    • -Description of current WFIS fire code
      • -some results


AND InfraRed Image


street patterns observed in fires
Street Patterns observed in Fires

Photo courtesy Brenner -observed in Florida

  • Infrared Camera
  • Inframetrics PM380
  • 3 to 5 mm
  • 256 by 256 array
  • Sterling cooler
  • 16 deg lens gives 1.4 mrad resolution per pixel
image flow analysis applications
Image Flow Analysis Applications
  • Understand fire behavior
  • Calculate combustion zone winds

and their statistics

  • Use derived data to validate

numerical models

image flow analysis
Image Flow Analysis


  • IR camera sees incandescent soot particles
  • Motion is on a distorted two-dimensional surface
  • Local features can be followed for short periods
  • We can fit data to simple types of motions, i.e. translation, rotation, dilation and shear


image registration
Image Registration
  • 1. Reduce image resolution (e.g. 7:1 in x and 5:1 in y)
  • 2. Align image using IR intensity center of mass
  • 3. Refine alignment using correlation analysis
      • = S (fn+1(x + Dx, y +Dy) - fn(x,y))2

Minimize L to estimate Dxand Dy.

4. Extract linear trends in Dx (t) and Dy(t).

  • 5. Registered IR images:
    • - used in image flow analysis to estimate winds within the combustion zone
image flow analysis1
Image Flow Analysis

Gradient Approach (Helmholtz theorem):

Two-dimensional motions can be represented as the

sum of six components.




Uniform expansion

And two shear componentswhich most researchers ignore.

robust statistics
Robust Statistics

Using the two components of translation,

we obtain the matrix equation

which we solve at each pixel for u and w. If |u2 + w2| > S2 then

we flag that pixel as an outlier and avoid considering it in future calculations. Typically, S= 20 to 40 m/s.

least squares minimization
Least Squares Minimization

After identifying outliers we sum over a patch of data as

We typically use 7 by 7 pixels.

Outlier points are not included in any of the summations.

This simplest approach requires the inversion of a

second order matrix to estimate u and w.


international crown fire modelling exp
International Crown Fire Modelling Exp
  • Canadian and US Forest Services
  • Near Fort Providence NWT Canada
  • Prescribed crown fires
  • 150 by 150 m plots
  • June – July 1997
  • Tower based IR
  • measurements
  • Plot 6–9 July 1997

Cameras on 50ft


wild fire experiment
Wild Fire Experiment
  • NCAR
  • Sept 1998, Montana, Colorado and California
  • Infrared Camera mounted on NSF/NCAR C-130
  • Wildfires were the target of opportunity
  • First case was in Glacier National Park

-Challenge Fire Complex 4 Sept 98

-100 m long hairpin vortex observed with IR

-fire about 2 km away from camera

ir imagery from c 130 fod part ii
IR Imagery from C-130FOD - Part II

Finger shot out

about 100 m in

1-2 sec

Indications of

burning fuel after finger retreats

Hairpin or Turbulent Burst

northern territory grass fire experiment australia
Northern Territory Grass Fire Experiment- Australia
  • Spear grass burns 40 km South of Darwin
  • Kerosene grass burns near Batchelor
  • Used 19 m high cherry-picker as platform
  • Platform motion requires apparent motion treatment
video ir data hughes plot 3
Video: IR Data Hughes plot 3

Camera @ 200 m from fire

giving @ 30 cm pixels

numerical model
Numerical Model
  • 3D Non-hydrostatic 2nd order finite-differences
  • Terrain following - geo-spherical coordinates
  • Vertical and horizontal grid refinement

– 2-way interaction

  • Vertically stretched grids with grid refinement
  • - Clark (1977,JCP), Clark-Farley(1984,JAS),
  • Clark-Hall(1991,JCP; 1996,JAM)
  • Boundary-Initial conditions from NWP
  • Bulk parameterizations of rain/ice processes

-Kessler (rain), Murray-Koenig (ice) and much more

recent approaches under development.


Horizontal Coordinates

Vertically Stretched Coordinates

multi processing approach
Multi-Processing Approach

Message Passing Interface (MPI) software is used

for multi-processing.

multi processing configuration for 3 layers nvrt 1 with tiling layer 1 details
Multi-Processing Configuration for 3 LayersNVRT=1(with tiling)Layer 1 details



Four sub-domains

per layer










grid refinement using 5 domains
Grid Refinement Using 5 Domains

Example from

Clark et al. 2000, JAS

Grid size ranges from

26 km to 200 m

(4:1 4:1 4:1 2:1)


domain 5 orography

Example from

Clark et al. 2000, JAS

rational for wildfire modeling
Rational for Wildfire Modeling
  • Wildfire propagation physics is poorly understood
  • FS spread models use empirical fits from
    • Low intensity small fires
    • Laboratory fire tunnels
    • Neither can hope to represent the vast parameter space of intense fires
  • Understanding fire behavior involves
    • Combustion winds interacting with the fire and ambient flow
    • Fire-atmosphere heat exchange
    • Fire-fuel heat exchange
    • Chemical release and transport by the convection
  • Some Applications of Coupled Fire-Atmosphere Models
    • Study burn paradigms
    • Understand fire related sources/sinks to atmospheric budgets
    • Develop suppression techniques
    • Like the NWP problem, fires are too non-linear to predict using empirically derived rule based techniques, i.e. there is no empirical fit to a severe nonlinear event.
ncar fire code

-Physical treatment of fire at a very ‘first cut’

level, i.e. useful for preliminary evaluation.

fire atmosphere coupling
Fire Atmosphere Coupling

The sensible and latent heat fluxes were added to

the vertical diffusion terms as:

Where Fs and Fiare the heat and moisture inputs from the

fire. Fs can reach values up to 1-3 MW m-2. .

Where as and al are extinction lengths for the sensible and

latent heat fluxes.

spread rate treatment
Spread Rate Treatment

BEHAVE formulation

fs is the slope coefficient

is the wind coefficient

is the wind normal to the fire front

R0 depends on fuel type and moisture content.

A BURNUP type curve is used to describe

the rate of mass loss for each fuel cell.

  • Strong need for improved spread rate
  • parametrizations appropriate for coupled
  • fire-atmosphere models
fire line propagation scheme
Fire Line Propagation Scheme
  • Contour advection scheme
  • Avoids assuming shape such as ellipse
  • We want the physics to determine shape
tracer code
Tracer Code
  • Grid point method used to
  • track fuel and fire
  • Four particles (or tracers)
  • for each fuel cell
  • Local contour advection
  • scheme used to move tracers
  • Area inside tracers designates ignited fuel
  • The Dx and Dy of fire model range from 10 to 300 m
  • Dz ranges from 5 to 10 m
  • Fuel cell Dxf and Dyf range from 5 to 60 m
fig 6 spot fires at t 200 s
Fig 6 Spot Fires at t=200 s

Kinematical test using

BEHAVE with fuel

class-3 (tall grass)

U= 3 m/s

line fire propagating over a hill
Line fire propagating over a hill
  • Slope about 60 percent
  • Nh/U about 1 giving deep evanescent modes
  • Without fire critical level amplifies wind speeds by about a factor of 3
  • Fire winds dominate ‘ambient flow’
  • Line spreads up hill with parabolic shape
  • Bifurcation occurs at hill crest
  • Vortex production along front
video buoyancy and enstrophy
Video: Buoyancy and Enstrophy

Red=2 deg Buoy

Purple= .1/s


weather fire integrated system wfis fire code
Weather Fire Integrated System(WFIS) FIRE CODE

-Physical parameterization of fire at the level of

sophistication where we can begin to compare with

the natural event.

Following results from

Clark, Griffiths,Reeder and Latham, 2003:Numerical

Simulations of Grassland Fires in the Northern

Territory, Australia: A New Sub-Grid-Scale Fire

Parameterization, J. Geophysical Research, (in Press)

  • Assume a time scale for combustion tb, e.g. 1-2 s.
  • Assume combusting material and air are two interacting fluids
  • The mixing ratio of the combustible material is Mf.
  • The burning portion of Mf has a volume mixing ratio mf.
  • The temperature of the combusting material is Tb.
  • The effective grid cell area of radiation is determined so that Tb (maximum) = 1200k. This assumption provides us with an effective volume/area (= lf) ratio.
  • Exchange of heat between the combusting fluid and the air is assumed to occur from:
    • Interfacial molecular diffusion using an ls length scale (without/with cases treated)
    • H20 and CO2 absorption. (not considered as yet)
  • Above assumptions designed for models using horizontal and vertical grid sizes of about 1 to 3 m.
governing equations
Governing Equations

Conservation equation for the mixing ratio of combusting material, Mf

Conservation equation for Mb (smoke)

governing equations1
Governing Equations

Thermodynamic equation for temperature of combusting material,Tb.

Conservation equation for q showing the fire-atmosphere heat

exchange terms.

Effective buoyancy that drives updrafts is now defined as


Figure 8.Horizontal and vertical cross sections from experiment CFA. (a) is at the surface, (b) is at x = 150 m, (c) is a section through y = 150 m, and (d) is taken at a height of 1 m.


Figure 6.Plan view of fire line at t = 1.4 min showing the wind vectors at z =2m above ground and plotted every 2 m for experiment CFA. The bold line marks the position of the fire front. Only a section of the domain is shown to highlight the variations along the fire.


Figure 7.(a) Maximum combustion temperature, (K), (b) spread rate (ms-1), (c) heat flux (MWm-2) and (d) total sensible heat flux (GW) from the fire versus time for experiment CFA.


Figure 2. at t = 24 s from a series of Australian grass fire experiments. The values of are 1., .5, .25 and .125 cm, respectively. The contour interval of is 8 K.

ls =.5 cm

ls =1 cm

ls =.125 cm

ls =.25 cm

  • Provided research funding is forthcoming we have a modeling framework that can be extended to the self-determining level by treating the fire-fuel heat exchange.
  • We can easily add new field variables to study the transport of various chemical species.
  • We can also treat additional physical effects through the addition of new field variables, e.g. break Mf into two variables to consider flashover effects.