We have all seen or heard on the media that “sweaty September” has been our warmest month ever – see “Australia in September 2013” from the Bureau of Meteorology (BoM)
I wrote to William Kininmonth ex BoM Senior Meteorologist(link to bio notes) – and asked if variations in the jet stream were affecting Australian climate.
He replied drawing my attention to this BoM map of September wind anomalies.
BOM archives monthly mean and anomaly charts at 850, 500 and 200hP.
September had an anomalous high sitting over SE Australia drawing in warm
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drawn in over south west Australia. In general terms the wind anomalies
bringing in warm/cool air coincided with the regions of warm/cool
temperature anomaly respectively. It would seem that the driver for the
temperature anomaly was the blocking situation, not global warming.
Mr Kininmonth has said he will answer questions here – and I wanted to add that his bio notes above came from the recent book he co-authored – Taxing Air
Temps just what you’d expect from the wind pattern.
Small detail on the minimum temperature map. Has the national night-time hotspot migrated from Walungurru to Giles?
I know the latter is a world-class climate reference station but maybe the paint’s fading or somebody’s been stuffing lolly-papers in the louvres?
Doesn’t stick out like Walungurru did yet but may be one to watch.
Dave, the national night-time hotspot seems to have been corrected out of post 2011 data – but when I just checked it is alive and thriving still in 2011 and the years 2002 to 2007. Not apparent in 2008 to 2010.
Mysteries of life stuff.
The dark red spot in Sep 13 minimum anomaly map is Forrest on the transline. But Giles does have a circular anomaly.
Warwick
Are you arguing that similar anomalies have never been present in the (recorded) past. Additionally are you also saying that this type anomaly produces the maximum heating response, in comparison to other anomalies in the (recorded) past?
What is you evidence for claiming this?
George
Any data on cloud cover anomalies? I looked the BoM site and couldn’t find any.
It’s my observation in WA that cloud cover is a big influence on temperatures.
George – are you asking about the Sep 2013 wind anomaly in the main article?
(I have added a link to that map too)
Comments just before yours drifted off-topic referring to the “national night-time hotspot”.
Warwick
Yes. If this type of wind anomaly has occurred before – why haven’t we seen similar temperature anomalies before? Are there other types of wind anomalies that will produce even higher temperature responses?
Hotter than normal conditions are because of prevailing (wind) conditions that support hot weather. Why is it the hottest ever, though?
George
In response to George Bailley’s question. Such wind anomalies have occurred previously. It is one reason why we get year to year variations in temperatures for particular months and seasons. Some years there is anticyclonic circulation over Australia and others there is a trough structure bringing cooler deep southwesterly winds over southeastern Australia. Often there are travelling waves bringing cold southerly then warm northerly airflow.
With a Blocking weather pattern there is persisting warm or cold, depending on the local wind direction. The 2003 heat wave of Europe was another blocking situation with warm air from North Africa directed over western Europe but cooler Arctic air over central to eastern Europe; the pattern has not been repeated in subsequent years. During September 2013 the blocking pattern produced warmth over central to eastern Australia but cooler conditions over southwestern Australia.
A legitimate question is, why does the atmospheric circulation throw up these blocking situations with persisting wind and temperature anomalies?
“Such wind anomalies have occurred previously” – so what is different this time – why was it the hottest on record?