C-Haines, Atmospheric Stability, and Fire-Atmosphere Interactions
C-Haines, atmospheric stability, and fire-atmosphere interactions
Graham Mills 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?
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
Stability Term: Stability Moisture term: Moisture 850-700 hPa Temperature Score 850 hPa Dewpoint Score Difference Depression Haines Index < 6C 1 < 6C 1 6 - 10C 2 6 - 12C 2
> 10C 3 > 12C 3
Expand the scale?
Lapse rate component and Haines Index
6
5
4 y = 0.5x - 2
3
2
Haines index component Haines index 1
0 2 4 6 8 10 12 14 Lapse rate (850-700 hPa)
Dewpoint depression component and Haines Index
8
7
6
5 y = 0.3333x - 1
4
3
Haines component 2
1
0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 850 hPa Dewpoint Depression 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 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
“SUBSIDENCE” LAYER
HEIGHT INVERSION LAYER
MIXED LAYER
TEMPERATURE
“SUBSIDENCE” LAYER
HEIGHT INVERSION LAYER
MIXED LAYER
TEMPERATURE 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 Index versus ingredients
• Ingredients approach is less categorical • Greater understanding • Indices can be “just” wrong
“SUBSIDENCE” LAYER
HEIGHT INVERSION LAYER
MIXED LAYER
TEMPERATURE
“SUBSIDENCE” LAYER
HEIGHT INVERSION LAYER
MIXED LAYER
TEMPERATURE 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: Simple plume dominated case Wind-driven ellipse (Coen et al 2013) 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? 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? 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?
Correlation coefficient (x100) at the selected locations for the relationship between the upper 40% of FFDI values correlated with C-HAINES > 4. 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) Alternative stability measures
• Ascent and descent energies (Potter) • Stability across entrainment layer (Mills) • Fire-CAPE (Potter) CAPE 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
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) 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