1. Lower atmospheric drying, stability, and increased wildfire activity
Graham Mills
Bureau of Meteorology Research Centre

2. Outline
Massive drying was observed at screen level during two major recent fires in Australia - Canberra - 18 January Eyre Peninsula - 11 January 2005
Why?
Was this that unusual?
How?
Predictability?

3. Locality map #1

4. Canberra 18 January 2003 (Mills, 2005, AMM)

5. Meteorological Context

6. Dewpoint

7. The northern dry band? GMS-5 Water Vapour Imagery
3-hourly intervals from 2030 UTC (~ 0500 LDST)
(first surface dewpoint drop ~ 0300 UTC)

13. Eyre Peninsula 11 January 2005

14. Meteorological context

21. Strong association with 300 hPa IPV

22. A general study? (encouraged by Potter, McCaw)
Stations spread across the southern fire-vulnerable regions
Td < -5C (want low moisture content, not just relative humidity)
to fire seasons (limit of half-hourly data archive)
WV imagery? - Front? - Dynamics?

23. Localities

24. So far……

25. How does dewpoint change?
Moisture equation: - Horizontal advection - Vertical advection - Diabatic processes: - evaporation - turbulent mixing

26. Early results? 68% have WV dry slot VERY evident
67% have front/trough passage - can be pre- or post-frontal
Climate control - marked interannual variability - dry soil > deeper mixed layers? OR wet soil > shallow inversion?
Daytime mixing - majority occur during day
Coastal marine layer erosion (YPLC)
Topographic interactions

27. High topography – lowering inversion overnight (Cabramurra)

28. Major circulation changes: Richmond – 2001-2002 fires

29. THEN - Upper tropospheric dry air – how does it reach the surface?
There’s usually a deep mixed layer, so maybe it doesn’t need a lot of help

30. Processes? Upper-jet circulations > dry intrusions
Mixing by cross-frontal circulations - surface-based fronts - mid-tropo. fronts / sloping b-l “lid”
Destabilisation by dry-slot (low e) air - (cf Haines Index concepts)
Positive feedbacks between upper IPV and lower frontal circulations?
……………?

31. Where next?
Monitoring WV imagery an immediate (fire) forecast /weather watch component
Complete station analysis and categorise
What are the dynamic controls on these events?
NWP model predictability (process good, results poor?)
Link to fuel moisture models