From Ward Rooney: Tuesday afternoon: I have put links to the visible pics and some low-level wind analyses on my web-page:
The maptool picture is in knots. On the the "lowest sigma level plots" , it looks like the barbs are knots and the contours are m/sec?
John McB
Date:
Tue, 28 Oct 2003 16:37:26 +1100
From:
Ward Rooney <w.rooney@BoM.GOV.AU>
To:
j.mcbride@BoM.GOV.AU
Subject:
Dust on Satpic
John,
Check
out the stream of dust showing up north of Broken Hill on Visual
Satpix
2Z, 3Z. 4Z - especially the 0400Z. Its a really impressive streak
of
dust.
Winds
through that area have been blowing 30 to 40 knots today, low
humidity,
and temps in the 30s.
A beaut day in the outback.
Ward
04
Z image
Maptool plot
Lowest Sigma Level Anal,
+03,
+06,
+09
Ward
Rooney: Later (around 6.30 pm)
Date: Tue, 28 Oct 2003 18:38:53
+1100
From: Ward Rooney <w.rooney@BoM.GOV.AU>
To: j.mcbride@BoM.GOV.AU
Subject: Last dust image
John
Last one before I go home.
Ward
06
Z image
John McBride.
Now...This last image (the 06Z) is really interesting. By this time the dust has become quite widespread. The low-level convection and stratocu is fairly widespread; but is suppressed over the region where the dust exists. Obviously there is some sort of radiative effect inhibiting convective/cloud development. Would anyone care to speculate?
John McB
Jeff Kepert
Date:
Wed, 29 Oct 2003 09:41:24 +1100
From:
Jeff Kepert <J.Kepert@BoM.GOV.AU>
I suspect there's some evidence
of boundary-layer rolls in the satpix. Look at the 04Z, there are
thin lines of clouds about 50 and 100 km to the south of the dust
band, and another 50 km to the north. They are visible also at 05
and 06. So perhaps the dust is in an ascending branch between two
rolls?
If so, the spacing is quite a bit wider than usual for cloud streets. BL rolls can have an aspect ratio (width/height) of about 2 to 15; if these are say 25 km wide (the cloud lines occur every second roll, on the upwards branch), and the BL 2 km deep (based on the Woomera sounding from that evening) this puts them at the upper end of the range. BL rolls normally drift slowly cross-wind, which the cloud lines and the eastern portion of the dust cloud seem to do.
And on the general dustiness, Clive Robertson on ABC FM this morning, when reading out the forecasts, highlighted that Toowoomba had a forecast he'd never seen in 30 years of being a radio announcer - "dusty". So, not just dust, but maybe even dust streets??
Jeff
Graham
Mills
Just looked at meso-viewer
low-level winds/temps. Suggests winds lifting dust were at/post-frontal.
Also shows that all that area was only very weak ascent/descent, with the
ascent area ahead of front and then "hooking" southwest, so cloudy areas
match larger scale ascent areas, clear (dusty) area matches larger scale
weak ascent or descent. Therefore radiational
effects (due to dust) suppressing
convection might not be the only hypothesis?
This reminds me yet again
(after the dust events last spring) of a paper I think I read, but can't
find, that presented the hypothesis that dust lifting was enhanced in regions
of strong, subsidence-enhanced, downward momentum transport. I guess that
if we invoke cross-frontal vertical circultion conceptual models, this
is superficially not inconsistent (love
the double negative) with
this case.
Graham
Harald
Richter
Jeff typed ...
> I suspect there's some
evidence of boundary-layer rolls in the satpix.
> Look at the 04Z, there
are thin lines of clouds about 50 and 100 km to
> the south of the dust
band, and another 50 km to the north. They are
> visible also at 05 and
06. So perhaps the dust is in an ascending branch
> between two rolls?
The 04Z image shows the dust
and the few Cu organised into curved banded structures. The maptool
image confirms the cyclonic curvature of the surface flow in W NSW.
Note the 06Z "propagation" of this organised banded pattern into central
and even E NSW (absent in the 04Z image).
Now, what could possibly
move that fast in 2 hours?
> If so, the spacing is
quite a bit wider than usual for cloud streets. BL
> rolls can have an aspect
ratio (width/height) of about 2 to 15;
I believe these aspect ratios
come from 60s theoretical deliberations first done by the likes of Lilly,
Faller and Kaylor etc. -- do all their assumptions hold in real life situations?
I like G.A.M.'s suggestion for the reason why so much momentum is slurping up the outback dust ...
> This reminds me yet again
(after the dust events last spring) of a paper I
> think I read, but can't
find, that presented the hypothesis that dust
> lifting was enhanced in
regions of strong, subsidence-enhanced, downward
> momentum transport ...
Without having looked at last nights mid-level flow analysis, is it just possible that a jet streak pivoted around the N side of that low in NW VIC?
Harald
Jeff
Kepert
>
> The 04Z image shows the
dust and the few Cu organised into curved banded
> structures. The
maptool image confirms the cyclonic curvature of the
> surface flow in W NSW.
Note the 06Z "propagation" of this organised
> banded pattern into central
and even E NSW (absent in the 04Z image).
> Now, what could possibly
move that fast in 2 hours?
>
I don't think what you see
is propagation, but development in situ (and a bit of advection). The thin
cloud bands lateral displacement between the 04 and 05 vis pics is
20 - 30 km ... this doesn't seem unreasonable (another double negative!)
for rolls to me. Although most of the roll studies are for straight
flow, they have been observed and theoretically
modelled in tropical cyclones,
so the curved flow certainly doesn't preclude them.
>
>>If so, the spacing is
quite a bit wider than usual for cloud streets. BL
>>rolls can have an aspect
ratio (width/height) of about 2 to 15;
>>
>
> I believe these aspect
ratios come from 60s theoretical deliberations first done
> by the likes of Lilly,
Faller and Kaylor etc. -- do all their assumptions hold
> in real life situations?
>
In fact the linear studies tend to get aspect ratios at the lower end of the range. The large aspect ratio cases are not well understood, not least because they are big to observe and so much of the evidence for their existence is from satpix, without detailed supporting observations. There is some suggestion that they can exist in conjunction with shorter wavelength features in the lower BL, and that the clouds only form over say every 3rd roll.
Jeff
Andrew Watkins
Date: Wed, 29 Oct 2003 14:34:51
+1100
From: Andrew Watkins <A.Watkins@BoM.GOV.AU>
Some interesting comments
on the dust storm in this arvos Sydney Morning Herald (I almost wrote "Harald"...).
Also
interesting, Blair, is the
quote of Cloncurry as Aust's highest max on record...
http://www.smh.com.au/articles/2003/10/29/1067233223834.html
Cheers,
Andrew.
---
Dr Andrew B Watkins
National Climate Centre
John McBride:
Herwith text of the Sydney Morning Herald Article:
Dust storm heads north
October 29, 2003 - 1:22PM
Wild weather continued its onslaught on Queensland today, with a dust storm
blanketing the state's south-east
corner.
Just days after weekend wind and hail wrought havoc on the Gold Coast,
strong westerly winds brought
choking dust.
"There was a big low pressure system which went through northern NSW yesterday
and we were getting
reports of raised dust from western Queensland today," said senior weather
bureau meteorologist Geoff
Doueal.
Visibility had been cut to around 200 metres in Coffs Harbour yesterday
but the storm had largely moved out
to sea today, he said.
At Brisbane airport, visibility this morning was around seven kilometres, instead of the normal 30 km.
An air traffic control spokesman said no planes had been grounded or diverted.
Today's storm was nowhere near as large as last year's massive dust storm
which was so vast it was visible
by satellite from space.
The storm front on October 23, 2002, was so large it stretched from Tasmania
to Mt Isa, removing tens of
millions of tonnes of topsoil.
Meanwhile, temperatures reached record levels for October in
western Queensland yesterday.
Meteorologist Ann Farrell said the Toorak (Toorak) research
station near the town of Cloncurry recorded 42.6 degrees
celsius, the highest ever in the state for October.
Mt Isa sweltered yesterday at 42.5 degrees, eight degrees
above average.
"For this time of year, temperatures are really out there," Ms
Farrell said.
But Queensland's high October temperatures were well down on
the state's highest ever recorded maximum when the mercury
reached 49.5 on December 24, 1972.
The all-time Australian record was at Oodnadatta in South-Australia in
January 1960 when it reached a
blistering 50.7 degrees.
AAP
Andrew
Watkins
Theres a great colour image
of the duststorm off the east
Australian coast available
from the earth observatory web site.
If you look at the high
res version (see link at bottom right
of image) you can see clearly
wave patterns within
the duststorm itself - very
very speccy. Comment gentlemen????
http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=11810
or via the home page (i
love this site...)
http://earthobservatory.nasa.gov/NaturalHazards/
Jeff Kepert
Andrew,
Truly a beauty ... not just transverse waves, but longitudinal banding also, and even with some little puffs of cloud sitting on the top of them (see attached excerpt - waves in the north, bands to the south).
So yet again the atmosphere refuses to succumb to the attempts by the lower surface (not to mention numerical modellers) to impose horizontal homogeneity.
Jeff
