Vindicated: Bureau Acknowledges Limits Set On How Cold Temperatures Can Be Recorded

The Bureau has a network of 695 automatic weather stations (AWS) across Australia. In a report released late yesterday it acknowledged issues with the performance of just two of these: Goulburn Airport (Goulburn) and Thredbo Top Station (Thredbo). These are the same two weather stations that I reported at my blog were not recording temperatures measured below minus 10 degrees on the 5th and 18th July, respectively.

While the Bureau strenuously denied it was setting limits, the Minister Josh Frydenberg nevertheless insisted on a review of the entire AWS network.

The Minister phoned me late yesterday to let me know that the report had just been published, and that the Bureau’s investigations confirmed that Goulburn and Thredbo were the only sites where temperature records had been affected by the inability of some Bureau AWS to read low temperatures.

What are the chances? Of the nearly 700 weather stations, I stumbled across the only two with problems.

Goulburn was discovered because my friend Lance Pidgeon lives nearby and was up early on the morning of 2 July concerned his pipes were going to freeze and burst – while watching the live AWS temperature readings tick-over on that weather station, then letting me know when the record for July of minus 10.4 was reached: only to see it rounded up to minus 10.0.

Thredbo was discovered because, after making a fuss about Goulburn, I wanted to check that the Bureau had actually lifted the limits on readings below minus 10. So, two weeks later I decided to get up early and watch the one-second reading at one of the stations in the snow fields on the Sunday morning of 16th July thinking it might be a cold morning. Why did I choose Thredbo – of all the weather stations in the Australian Alps? Simply because my school friend Diana Ainsworth died in the landslide there twenty years ago.

Never mind – I’m vindicated!

The Bureau has now acknowledged that it had inadvertently set limits on how cold temperatures could be recorded at Goulburn and Thredbo.

To be clear the equipment has a general operating range to minus 60 degrees Celsius, but smart card readers – with a nominal range to only minus 10 degrees Celsius and that stop reading all together at minus 10.4 – were inserted placing limits on the actual recordings, not the measurements.

According to the report published late yesterday, the cards were inserted into the Goulburn weather station in September 2002, and into the Thredbo weather station in May 2007. So, for a period of nearly 15 years there has been a limit on how cold temperatures can be recorded at Goulburn, and for nearly 10 years at Thredbo.

This Goulburn weather station was first opened in 1990, and had previously recorded temperatures below minus 10 degrees Celsius in 1994,1999 and 2000 – with a record cold minus 10.9 recorded on 17 August 1994.

The Thredbo weather station opened in 1966, and recorded an average of 2.5 days below minus 10 degrees until 1996 when an automatic weather station was installed – replacing the previous liquid-in-glass manually-read thermometers.

Since the AWS was first installed, back in April 1997 there has been a reduction in the average number of days when temperatures have fallen below minus 10 degrees Celsius, as shown in the chart.

Further, since May 2007 when the MSI2 sensor interface card was replaced with the MSI1 card (see page 50 of the new report from the Bureau) there has been no potential to record below minus 10.4. Yet not far from this location, at Charlotte Pass, an all-time record low temperature of minus 23 degree Celsius was recorded on 29 June 1994; this was with an old style liquid-in-glass thermometer – not with an AWS.

How can this review possibly conclude that there are no problems with the other 693 automatic weather stations – and there has been no impact on official temperature records from the limits it now acknowledges were placed on recordings from Thredbo and Goulburn?

Surely, there is now evidence enough for a proper external review to be initiated, this should be a Parliamentary Enquiry, through the House Energy and Environment Committee.

The Bureau’s report can be downloaded here: www.bom.gov.au/inside/Review_of_Bureau_of_Meteorology_Automatic_Weather_Stations.pdf

Originally published on Dr. Jennifer Marohasy’s blog