Archives for September 8, 2017

TWO decades ago the Australian Bureau of Meteorology replaced most of the manually-read mercury thermometers in its weather stations with electronic probes that could be read automatically – so since at least 1997 most of the temperature data has been collected by automatic weather stations (AWS).

Before this happened there was extensive testing of the probes – parallel studies at multiple site to ensure that measurements from the new weather stations tallied with measurements from the old liquid-in-glass thermometers.

There was even a report issued by the World Meteorological Organisation (WMO) in 1997 entitled ‘Instruments and Observing Methods’ (Report No. 65) that explained because the modern electronic probes being installed across Australia reacted more quickly to second by second temperature changes, measurements from these devices need to be averaged over a one to ten-minute period to provide some measure of comparability with the original thermometers.

This report has a 2014 edition, which the Bureau now claim to be operating under – these WMO guidelines can be downloaded here:
http://www.wmo.int/pages/prog/www/IMOP/CIMO-Guide.html .

Further, section 1.3.2.4 of Part 2 explains how natural small-scale variability of the atmosphere, and the short time-constant of the electronic probes makes averaging most desirable…  and goes on to suggest averaging over a period of 1 to 10 minutes.

I am labouring this point.

So, to ensure there is no discontinuity in measurements with the transition from thermometers to electronic probes in automatic weather stations the maximum and minimum values need to be calculated from one-second readings that have been averaged over at least one minute.

Yet, in a report published just yesterday the Bureau acknowledge what I have been explaining in blog posts for some weeks, and Ken Stewart since February: that the Bureau is not following these guidelines.

In the new report, the Bureau admits on page 22 that:

* the maximum temperature is recorded as the highest one-second temperature value in each minute interval,

*the minimum is the the lowest one-second value in the minute interval, and

* it also records the last one-second temperature value in the minute interval.

No averaging here!

Rather than averaging temperatures over one or ten minutes in accordance with WMO guidelines, the Bureau is entering one second extrema.

Recording one-second extrema (rather than averaging) will bias the minima downwards, and the maxima upwards. Except that the Bureau is placing limits on how cold an individual weather station can record a temperature, so most of the bias is going to be upwards.

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

I’ve also posted on this report, and limits on low temperatures, here: https://jennifermarohasy.com.dev.internet-thinking.com.au/2017/09/vindicated-bureau-acknowledges-limits-set-cold-temperatures-can-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 Diane 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 per year 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 per year 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