More on the cold-front that passed through eastern Victoria on the evening of 7 January (i.e last Tuesday evening).  According to the website of the Victorian Department for Sustainability and the Environment (www.nre.vic.gov.au), almost 100 fires were triggered by lightning during this frontal passage.   This is interesting in that  it implies widespread fires in southeastern Australia are not always caused by human activities  and so must have been a common event in pre-european settlement times, and possibly even pre-history.  The fires presumably would have affected the development of ecosystems in the region.

Moving down to the more immediate timescale, why so much lightning: why so many fires?

I have placed the soundings for Melbourne Wednesday morning (2300 UTC 7 January), and for Wagga Thursday morning on my webpage.  Both traces are for after the surface frontal passage.  You'll see the instability is not particularly large.
(though that does depend a bit on where in the boundary layer you source the parcel, if you are looking at the prefrontal sounding). However,on both traces, you'll see the character of the change itself is interesting:  The cold air is through quite a deep layer (surface to 700 hPa) and then cuts off sharply, with an unaffected atmosphere above: there is no sign of any upper level cutoff/cold pool at 500, say.

So what happens when you have a 300hPa deep layer of cold air undercutting the ambient pre-frontal atmosphere:  You must get a real whoomp of vertical motion above that layer, setting off thunderstorms with very high bases (viz 700 hPa bases). This presumably is what triggered all the lightning strikes.

I have also put on my web-page a gif image of the locations of fires as of this morning.  Unfortunately I didn't know about the NRE webpage back on Wednesday when we would have had 100 red spots on this map.

Cheers
John McB

Gary Weymouth
Re development of ecosystems and fires:

Old paintings of bush scenes often show relatively sparse gum trees in grass.  In many areas, the current dense bush and especially understory is probably the result of European forest management - a recent anomaly.

I have heard similar from a NRE ranger, but have not chased up any refs.

In any case, we all know about the ability of gums to regenerate after bushfires which are not too severe - indeed the need of fire that gums  have.

Gary

Milton Speer

More ecological thoughts -

Smoky Cape on the NSW mid-north coast was so-named by Captain Cook because
when he first sailed past he noticed that the area was shrouded in smoke haze
supposedly from fires lit by local inhabitants (according to the Smoky Cape
Lighthouse museum). That area is a pretty good candidate for summer lightning
strikes as well. Can't recall the time of year Cook sailed past it though.

Milton

Robin Hicks

It appears Captain Cook passed Smoky Cape sometime between 12 and 15 May 1770.

See below (from
http://pages.quicksilver.net.nz/jcr/~cookbio2.html
 

Cook, though, was too far north and when, on April 19th, Cook's second-in-command Zachary Hicks sighted land it was part of the mainland of New Holland that he saw. The exact position remains in doubt but a headland in East Victoria is called Point Hicks to mark the event (on some maps it is called Cape Everard).
The Endeavour then turned east and north past Cape Howe to begin what would be a long journey up the East Coast of Australia. Because of conditions, including heavy surf, Cook kept the ship a safe distance from shore and
several good harbours were missed as a result. No landings were attempted until April 28th. Just north of Red Point and present-day Wollongong, Cook tried, first in the pinnace, and then in the yawl to land at Bulli but the surf swamped the boats and prevented them getting ashore.
 

Botany Bay.
The next day, April 29th 1770, the Endeavour sailed into a large bay and anchored just off the inner shore of the southern point of the bay. People were seen onshore but when a party landed (led by Isaac Smith, a cousin of Cook's wife) all but two of them ran away. Conversation was tried with the two who remained but no one, including Tupaia, could understand or be
understood. The situation worsened, the British fired their guns and the Aborigine men from the Gwiyyagal Tribe threw their spears. For the rest of the stay no further contact took place. The Aborigines would watch from or follow at a distance, as happened when Lieutenant Gore made a journey up the bay to collect oysters. Cook made several excursions around the bay including one up a river on the north side where they explored inland and commented on soils and vegetation
(this river, near Sydney Airport, is now called Cook's River). A crewman, Forby Sutherland died on May 1st and was buried near the landing point (the inner point was named for him). Spores and tracks of animals were seen but actual sightings were unsure (a small rat-like animal may have been a wombat). Banks and Solander collected many botanical specimens, occasioning the bay's eventual name. At first it had been called Sting-ray Bay after the many fish that had been caught.
 

The East Coast of New Holland.
On May 6th Cook took the Endeavour out of the bay and headed north once more soon passing an inlet he named Port Jackson that would become the site of Australia's first European settlement. This settlement eventually became Sydney. By the 11th they had passed Port Stephens and Cape Hawke. Cook was conducting a running survey as he went along the coast and compiling a chart but he was more intent on reaching home so made little effort to land anywhere. He called three high hills he saw on May 12th, the Brothers, while a point further north, where he could see fires alight, he called Smoky
Point.
The Endeavour sailed past the Solitary Islands to arrive at Cape Byron on the 15th. Behind the cape Cook could see an inland mountain and, when dangerous rocks were encountered, the mountain later acquired the name Mount Warning. A cape near the dangerous rocks was called Point Danger, while a nearby small island later became Cook Island. The point that Cook called Point Danger is now called Point Fingal while the name Point Danger has been applied to another point just to the north at present day Tweed Heads. Cook next sailed outside two large islands without being aware of them being
islands. He gave the name Point Lookout to the northern point of the first island (North Stradbroke Island) and the name Cape Morton to that of the second island (Moreton Island - Morton later gained a letter 'e'). Cook suspected but did not see the large bay behind the islands, now known as Moreton Bay, nor the river that flows into the bay (Brisbane stands on that
river).
 

Robin Hicks
SRDM
National Climate Centre

 Harald Richter

> Moving down to the more immediate timescale, why so much lightning: why so
> many fires?
>
> I have placed the soundings for Melbourne Wednesday morning (2300 UTC 7
> January), and for Wagga Thursday morning on my webpage.  Both traces are
> for after the surface frontal passage.

I am getting broken links here .. but from memory, the pre-change boundary layer sported fairly low relative humidities.  Given a decent depth of the cold air,  pre-change parcels would have enjoyed deep lift presumably sufficient to initiate
high-based storms.  Rain falling out of high-based storms into a deep dry sub-cloud layer would mostly evaporate, while CG lightning can hit fuel that remains dry despite the 'rain aloft.'

Harald