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C-Haines, atmospheric stability, and fire-atmosphere interactions
Graham Mills
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Outline
• What’s C-Haines?
• Indices versus ingredients
• Atmospheric stability
• What’s fire-atmosphere interactions?
• When might C-Haines work?
• What limits operational use of atmospheric stability measures?
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The Haines Index
• Developed by Don Haines
• Two stations, two year’s data
• Intended to pick the 5% of days when erratic fire behaviour likely
• Caveat : only plume-dominated fires
• Some relationship with area burnt in Idaho, Florida, and Tasmania
• Less-good in southwest US, Victoria, WA
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Haines Index
Stability Term:
850-700 hPa Temperature Difference
Stability
Score
Moisture term:
850 hPa Dewpoint Depression
Moisture
Score
< 6C 1 < 6C 1
6 - 10C 2 6 - 12C 2
> 10C 3 > 12C 3
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Expand the scale? Lapse rate component and Haines Index
y = 0.5x - 2
0
1
2
3
4
5
6
2 4 6 8 10 12 14
Lapse rate (850-700 hPa)
Ha
ine
s i
nd
ex
co
mp
on
en
t
Dewpoint depression component and Haines Index
y = 0.3333x - 1
0
1
2
3
4
5
6
7
8
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
850 hPa Dewpoint Depression
Hain
es c
om
po
nen
t
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Characteristics
• Little diurnal cycle
• Solid annual cycle
• Can “spike” or can remain high for some days
• Climate is regional, and this is probably implicit in local fuel and fire response
• Usually high on very active fire/pyrocumulus days
• Case studies show some active fires in lower/decreasing FDI but extreme C-Haines
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What does it mean? Potter and Haines argued
• That the lower Haines level should be above the mixed layer
• That the Haines Index is not valid if the lower level is in the mixed layer
• That the Haines Index is only valid for plume-dominated fires
• That the HI showed when the atmosphere was sufficiently unstable to mix dry air to the fire
• They did not propose any physical processes that would explain this mixing
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MIXED LAYER
TEMPERATURE
HE
IG
HT
INVERSION LAYER
“SUBSIDENCE” LAYER
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MIXED LAYER
TEMPERATURE
HE
IG
HT
INVERSION LAYER
“SUBSIDENCE” LAYER
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Index versus Ingredients
• Index : an easily-derived quantity that has some statistical relationship to a desired forecast quantity
• Ingredients: instead of combining everything into one number, look for the physically meaningful quantities that all have to be valid in order for a given event to occur
• Eg : Thunderstorm forecasting
• Meteorological focussing of ingredients
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Index versus ingredients
• Ingredients approach is less categorical
• Greater understanding
• Indices can be “just” wrong
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MIXED LAYER
TEMPERATURE
HE
IG
HT
INVERSION LAYER
“SUBSIDENCE” LAYER
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MIXED LAYER
TEMPERATURE
HE
IG
HT
INVERSION LAYER
“SUBSIDENCE” LAYER
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Fire-atmosphere interactions
• A fire obviously affects the atmosphere around it
• Heat and moisture release warms and moistens the local environment
• This will affect the winds in some way
• What the feedbacks will be are less obvious, as they will depend on the “Ingredients”
• Eg:
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Simple plume dominated case
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Wind-driven ellipse (Coen et al 2013)
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Coupled studies
• Simpson and Sharples
• Kiefer et al
• Thurston?
• Peace
• All show great stuff - BUT do they tell us anything about atmospheric stability and fire atmosphere interactions?
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Fire-atmosphere interactions
• From a forecast point of view, a more stringent (personal) requirement: “THAT FIRE-ATMOSPHERE INTERACTIONS PROVIDE A FEEDBACK ON FIRE BEHAVIOUR”
• So when might C-Haines be useful?
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Relationship with FFDI?
• High temperatures at 850 hPa - correlate to high FFDI (T and RH) ? - correlate to high Haines-A ? - correlate to high Haines-B ?
• Low dewpoints at 850 hPa - correlate to high FFDI (RH) ? - correlate to high Haines-B ?
• So does (C-)Haines add anything to FFDI?
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Correlation coefficient (x100) at the selected locations for the relationship between the upper 40% of FFDI values correlated with C-HAINES > 4.
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When to use?
• Perhaps concentrate on the medium-ish FDI events
• Use local climatology percentile values to indicate relevance
• Quite a few examples of unusually lively prescribed burns, or wildfires after peak of FDI activity, but still >95th percentile CH
• Quite a few of these are elevated above the (generally) lower-elevation AWS (intriguing)
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Alternative stability measures
• Ascent and descent energies (Potter)
• Stability across entrainment layer (Mills)
• Fire-CAPE (Potter)
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CAPE
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FIRE-CAPE (Potter)
• Add the temperature and moisture increment due to the fire to environmental values and recalculate CAPE
• It cannot be less than CAPE
• Is it relevant if there is no condensation?
• How might it affect a fire?
• There’s very limited evidence of correlation association with fire activity
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Bringing this together
• C-Haines is an index
• Apart from Tasmania, there’s no statistical evidence for a relation with fire activity in Australia
• There is just enough examples of fires in low FDI/high CH environments to make me think there still might be something there
• We don’t know what the physical processes are that might make fires more active in high CH environments
• We don’t have the fire activity data-bases to do a statistical analysis (ideally down to hourly measures)
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A way forward (?)
• Trial use of C-Haines and/or Fire-CAPE and/or …. with systematic evaluation against fire activity (incl null case)
• Much more research to understand vertical fire-atmosphere coupling processes - might lead to ingredients approaches - ultimately operational coupled forecasts
• Better fire behaviour data bases
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