Stability, Fire Behaviour and the Haines Index MODIS Image, 1 Jan 2007, Smoke from Great Divide Fires

Introduction In Australia we use the McArthur Fire Danger Indices to give an indication of fire danger One of the limitations of these indices is that they do not take into account the stability of the atmosphere Why is stability important for fires? ?

Stability Indices The most common index used to capture the stability in a fire weather context is the Haines Index. Before we look at that, let’s start with something more familiar… The surface lifted index (SLI) is used regularly for thunderstorm forecasting How is the SLI calculated? ?

Surface Lifted Index to 500hPa = T env(500hPa) – T parcel(500hPa)

Haines Index is like SLI In a fire weather context we still want to know information about the lapse rate, but we’re looking for a dry atmosphere, not a moist atmosphere Who can explain how the Haines Index is calculated? ?

_________________________ Haines Index = Stability Term (A) + Moisture Term (B) _________________________ Values range from 2 to 6: “low” when H < 4 “moderate” when 4<=H<5 “high” when H>=5

Use data from just above highest orography in the region

Haines Index A “bad” fire day has a HI=6

Example Haines Calculation We will calculate the Haines Index from Black Saturday (Feb 7, 2009) What Haines Index would we expect? ?

Black Saturday Haines Index (850hPa T – 700hPa T) = (27 – 13) = 14

Stability Score = 3

Black Saturday Haines Index (850hPa T – 850hPa Td) = (27 – -1) = 28

Moisture Score = 3

Haines Index = 6 Australian Broadcasting Corporation

A quicker way… A Haines Index calculator is available at http://www.tas.bom.gov.au/reg_progs/sev_wx/haines/haines_calc.html

In Australia there were too many “high” Haines Index days The data that Donald Haines used in deriving his original index showed that only 5% of days were “bad” days (HI=6). But in Australia the number of days with a HI of 6 was much higher, leading to an index that didn’t highlight the significant days very well. Figure 2. Percentage of days between September 1 and 30 April for the years 2000-2007 inclusive for which the mid-level Haines Index is greater or equal to 5 at the selection locations (Mills and McCaw 2010)

The original Haines Index was designed for mid latitude Northern America and correspondingly it has been used in its original form mostly in Tasmania. In lower latitudes the index is at its maximum value on most days of the fire season. This has lead to the consideration of a continuous Haines Index together with the development of a climatology so that occurrences above the 95th percentile or other threshold can be identified. Graham Mills

Continuous Haines Index CH = CA + CB CA = 0.5(T850 -T700 ) - 2 CB = 0.3333(T850 -Td850 ) - 1

In practice it has been found that occasional very large dewpoint depressions in the LAPS analysis data set, together with the non-linearities of the hypsometric equations, occasionally caused the CB term to become disproportionately large, and so two conditions were applied. The latter condition reduces the slope of the DPD relationship for dewpoint depressions greater than 18oC, while the former limits the upper value of CB. Graham Mills

Continuous Haines Index if (T850 -Td850 )>30, then (T850-Td850 )=30 and if CB > 5, CB=5 + 0.5(CB – 5) In practice it has been found that occasional very large dewpoint depressions in the LAPS analysis data set, together with the non-linearities of the hypsometric equations, occasionally caused the CB term to become disproportionately large, and so the following two conditions were applied: if ( T850 - DP850 ) > 30C, then ( T850 - DP850 ) = 30C (4) and if CB > 5., then CB = 5. + ( CB - 5. ) / 2. (5) The latter condition reduces the slope of the DPD relationship for dewpoint depressions greater than 18C, while the former limits the upper value of CB.

Continuous Haines Index A “bad” fire day has a CH ~ 13

Black Saturday C-Haines CA = 0.5(T850 -T700 ) - 2 = 0.5(27 – 13) -2 = 5

Black Saturday C-Haines CB = 0.3333(T 850 – Td 850) - 1 =0.3333(27 – -1) -1 = 8.33 But if CB > 5,CB=5 + 0.5(CB – 5) so CB=5+0.5(8.33-5) = 6.67

C-Haines Index = 11.67 Australian Broadcasting Corporation

Black Saturday C-Haines 1600hrs

Climatology of C-Haines 95th percentile value of C-HAINES (multiplied by 10) at the sampled gridpoints. Data is at 0600 UTC for the months of September to April inclusive, years 2000-2007. (Figure 5 from Mills and McCaw 2010 )

C-Haines is routinely calculated as a grid in GFE

Limitations of Haines Index and C-Haines What are the limitations of using an index like Haines Index? How would you overcome these limitations? ? ?

Summary Haines Index is a simple measure of the instability and dryness of an airmass The C-Haines is a more sophisticated version of the index and is calibrated to highlight significant days in Australia It is important to look at the whole temperature sounding, not just the value of the index

Further training COMET module: Stability, Smoke Management and Fire Weather Forecasting © iStockphoto/bmtc