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Cold outbreaks in southern Australia in summer

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crikey
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Cold outbreaks in southern Australia in summer

Post by crikey »

COLD OUTBREAKS IN SOUTHERN AUSTRALIA IN SUMMER
The first article investigates the uncanny similarities between the Christmas day 2006 cold snap and the Jan 2012 cold snap
In particular the near identical pattern of the surface synoptic pattern and the 200mb upper winds/jet-stream position and shape
The correlation of the synoptic pattern was virtually identical at the same seasonal period Dec 26th 2006 and Jan 11th 2012 ( summer)
The 200mb air pattern was identical for the DEC 25th 2006 summer cold outbreak and the Jan 11th 2012 cold outbreak

I was very excited at this find as the two events were noteworthy and broke some long standing records
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Came across this article when reading about cold outbreaks and 'clicked' the set up of the 2 events was identical

Found this excellent study by the earth science dept of Melbourne university
A pdf file
http://www.bom.gov.au/events/9icshmo/ma ... hcroft.pdf" onclick="window.open(this.href);return false;

Cold outbreaks in southern Australia
Ashcroft et al
University of Melbourne ( earth science dept)
written after 2008 ( no exact date given on document)

Quote
"The primary mechanism behind Cold Outbreaks is
surface anticyclone/cyclone dipole located over the
affected region. A strong geostrophic wind anomaly
between the two systems is created, forcing cold
advection and an equatorward incursion of high
latitude air (see Konrad, 1998 for North America;
Simmonds and Richter, 2000 for Australia; Marengo
and Rogers, 2001 for South America). An example
of this is shown in Figure 1 which presents the mean
sea level pressure (MSLP) and 925hPa vector winds
associated with a Cod outbreak in Melbourne on December 25,
2006. This particular Cold outbreak resulted in the coldest
December day in Melbourne for 50 years, with
maximum temperature of 14.5°C."
Image

http://www.bom.gov.au/events/9icshmo/ma ... hcroft.pdf" onclick="window.open(this.href);return false;

NOW have a look at this similarity. SNAP !!
Now here is the jan 11th 2012 synoptic pattern. The synoptic is identical with the same anti-cyclone/cyclone dipole!
Image

Now also the upper air 200mb and jetstream pattern were identical


JET stream pattern in jan 2012 event
200mb upper air jetstream arch. The western flank directing upper air up from the south

Image

and a zoom out view of jetstream shows quite a bulge northward out of the main latitude band
Image

source:
http://virga.sfsu.edu/gif/jetstream_sohem_00.gif" onclick="window.open(this.href);return false;


The 200mb air pattern was similar/identical for the dec 25th 2006 summer cold outbreak and the jan 11th 2012 cold outbreak
Here is a snap of the 200mb upper air for the 25 th dec 2006 from archives indicating the same shape an position of the upper air for both events
http://www.bom.gov.au/cgi-bin/charts/charts.browse.pl" onclick="window.open(this.href);return false;

Image



Some news archives from 2006
I believe there was snow in parts of vic and melbourne
Here are some news links from the archives
http://www.heraldsun.com.au/news/victor ... 1112737045" onclick="window.open(this.href);return false;
Dec 25th 2006
"Gusts nearing gale force have been recorded at the bureau's Frankston automatic weather station throughout this morning."

and in jan 2012 a similar story
record winds at st kilda ..122km/hr

another article with some good stat's and pic' 2006
http://www.heraldsun.com.au/news/victor ... 1112738809" onclick="window.open(this.href);return false;

a report from the 23rd dec 2006 just before the christmas day event
http://www.theage.com.au/news/national/ ... 45881.html" onclick="window.open(this.href);return false;

2006
According to wunderground archives melbourne had a minimum record of 6 deg C
http://www.wunderground.com/history/air ... e=Victoria" onclick="window.open(this.href);return false;



2012 Event played out quite similar. Not as much snow but the cold pressed into NSW with records in both VIC and NSW
Some comments by AWF members re the cold snap of Jan 2012
Event thread
http://www.theaustralianweatherforum.co ... &start=140" onclick="window.open(this.href);return false;

Johnno
6 places in NSW last night had their coldest Night ever for January including Canberra with a Minimum of only 1.6c! (Bom were forecasting 6c) Phenomenal for Mid January and Mid Summer! Mt.Hotham only had a Maximum temp of 0c Yesterday which meant it had its coldest Maximum temp ever for January and the coldest daytime temp in January over the mainland to ever be recorded in January.

Norfolk
and dont forget, yesterday was the first time since 1984 that no place in NSW recorded a temp of 30 or above!
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i wondered if there were any similarities with the AAO index as well ,but l found that NOT to be the case
OBSERVATIONS from the AAO( antartic oscillation)
In the Janaury 11th/12th cold snap the Antartic oscillation index had been strongly positive for about 50 days but in the dec 2006 cold snap the AAO was negative . So i would think the AAO had no direct impact on the cold snap event . ( not directly correlated)
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Re: Cold outbreaks in southern Australia in summer

Post by Rivergirl »

Wow, thanks for all that info crikey, so much detail. It's really interesting to see the similarity in the two years. I remember in 2006 it snowed on Christmas Day up here in the hills
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Re: Cold outbreaks in southern Australia in summer

Post by Australis(Shell3155) »

I went to Doona Buang that day and have some lovely xmas day snow photo's.
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Re: Cold outbreaks in southern Australia in summer

Post by crikey »

Glad you found the comparison interesting Rivergirl!
I missed the snow being inland Australisshell but do remember the news reports
Thought l would go a little further into comparing the analysis of the cold outbreaks. ( 25th dec 2006 and Jan 11th/12th 2012)
and firstly for anyone who reads this, this is not a professional analysis but a speculative analysis from an amateur. LOL :D

As well as the uncanny similarities in the surface synoptic There is also strong similarity in the 200mb geopotential height anomalies.
The anomalies in DEC 2006 and 2012 are incredibly similar
Both indicating strong below mean low anomalies in the polar region and strong high anomalies in the band around the polar region( sub -polar), providing a strong gradient between the 2 pressure bands at 220mb.
Firstly the lower anomaly in the polar region provided cooler than normal temps at 200mb level and higher temps in the high pressure band( sub polar band ) adjacent.
This could have produced some strong temp gradients and strong circulation flows in the polar and sub-polar region ( maybe some strong jetstream arches?)
(It is also worthwhile noting the subtropical jetstream has been riding very high toward the equatorial zone during this time period.)

The temps at Casey weather station had been about 2 deg c below the mean in week 2 jan 2012 .
The cooler anomalies of temps at the surface,mid and upper air coupled with a strong circulation in the polar/sub polar band could have assisted in bringing the colder polar air into VIC and NSW

ANOMALIES

Just check out those 220mb geopotential height anomalies for the DEC 2006 and DEC 2011 !!
The Dec 2011 200mb anomaly is just insane!!
:o 8-)


Sorry things aren't in order. I have hand labeled each one ..
Anomaly maps from BOM. Thanks!
http://www.bom.gov.au/cgi-bin/climate/cmb.cgi" onclick="window.open(this.href);return false;

Image



Image

Some anomalies from the cold snap events
Notice the generally colder temp anomalies
and
the high and low anomaly couplet in the 220mb geopotential height ( the polar/ sub polar circulation region)...3rd map down

( l made an assumption that the anomalies for JAN 11th 2012 would be similar to DEC 2011 mean. being the GENERAL state of the atmosphere at the time)

Image
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