From: Andrew Tupper <andrewt@BoM.GOV.AU>
Dear all,

I'm composing a reply to the E-mail below from Ima Itikarai of Rabaul
Volcano Observatory in Papua New Guinea.  He has just led a team to
investigate reports of activity at Lamington, a dangerous volcano on the
PNG mainland.  Along the way he came across what appears to be downburst or
microburst damage, as described below.

I'll be sending him a reply and summarising the imagery and the synoptic
situation, but I did wonder - has anybody encountered or heard of downburst
damage like this in PNG?  How would 'strong winds that went on for 1-2
hours' fit in?

Thanks, Andrew Tupper,
Northern Territory Regional Office
 

>Dear Andrew,
>
>While I was in Popondetta doing investigations on Lamington volcano, I
>came across an area  covering approximately 400mx200m with many up-rooted
>trees.  Some broke half way up. The coordinates of the location is:
>8.8215°S and 148.1029°E. Many of the trees were huge. Biggest about 1-1.5
>m in diameter and 20-30 m tall. Accordnig to local people the trees were
>uprooted by strong winds that went on for 1-2 hours. An interesting
>observation was that there were no fallen trees up-wind (southward) or
>down-wind (northward) to indicate the trail of the strong wind suggesting
>the wind was not directional (this may be contradicted by the direction of
>the uprooted trees) but rather a spot, say like a tornado of whirlwind.
>Incidentally, no houses were blown over or destroyed. The incident
>happened on 6th April 2002. Is it possible to check your sattelite images
>of weather patterns on this day around location provided.
>
>Regards.
>
>Ima.

 Cathy Muller

>Hi Andrew,
>
>I haven't heard of downburst activity lasting for 1 to 2 hours, nor a
>tornado, but who is to say that it was just a single event and not one or
>more "merged".
>
>I have had a look at the IR imagery, and from that I am assuming that the
>event(s) was/were during the morning hours. (The afternoon imagery looks
>pretty benign!)
>
>I reckon Gordon Jackson would be able to give you some interesting PV
>charts for that day, which may help.
>
>I would be interested to see what you conclude.
>
>Cathy.
>
>PS...Can you tell me how I can join this email list? I only got this
email
>through Jeff Callaghan.
 

Andrew Tupper
Thanks Cathy for the IR imagery.  I had a look at the vis too.  The only
explanation that I can think of to account for the "1-2 hours" of wind is
that the storm complex was fairly extensive - so the winds would have been
gusty for a while around the populated areas near the affected forest,
even
though the downburst that did the damage was short lived.  Hopefully
nobody
was under the trees at the time, so nobody could measure the duration of
the severe winds.  Does this sound reasonable?

Gordon's off on a jolly at the moment, but I've had a look at our analyses
for the period as well as Matt Wheeler's page at
http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/OLR_modes/index.html
. It was an interesting period - there was lots of convergence from
easterlies to the south, there was a strong n=1 Equatorial Rossy wave
moving through, and TC 'Bonnie' formed a couple of days later in the Timor
Sea.  But maybe you don't need this kind of environment to get a downburst
in Papua New Guinea?  Maybe they get them every day, and this one was only
nusual in that it happened near a heavily populated area?

cheers Andrew