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Jennifer Marohasy

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Archives for September 11, 2017

Bureau Management Rewrites the Rules – Again

September 11, 2017 By jennifer

Following is the latest advice from the Australian Bureau of Meteorology regarding measurement of temperatures from automatic weather stations (AWS). This advice contains numerous errors of fact and is inconsistent with the information in an internal review issued just last Thursday.

The following misinformation has just been posted at the official Bureau website:
http://www.bom.gov.au/inside/AWS_Review_Fast_Facts.pdf

My responses to the inaccuracies in this document are prefaced with JM, and inserted herein.

FAST FACTS: How does the Bureau measure temperature?

1. The Bureau measures air temperature using an electronic sensor (a platinum resistance thermistor) placed within a Stevenson Screen, and temperature is recorded every second.

JM: No. The temperature is measured every second, it is not recorded every second by the Bureau. Rather, the Bureau has explicitly stated, most recently in an internal report released just last Thursday, that for each one minute temperature it only records the highest one-second temperature, the lowest one-second temperature, and the last one-second temperature – in that one minute interval. The Bureau does not record every one-second value. In the UK, consistent with World Meteorological Organisation Guidelines, the average temperature for each minute is recorded.

2. The air temperature fluctuates frequently on the scale of seconds. By using a sensor which has a longer response time than the fluctuations of the air temperature, the sensor “averages” these fluctuations.

JM: No. Electronic sensors have shorter response times than mercury thermometers. So, to ensure there is no discontinuity in measurements when the transition occurred from mercury thermometers to electronic probes the maximum and minimum values need to be calculated from one-second readings that have been averaged over at least one minute.

3. Both the mercury-in-glass thermometers, and the electronic sensors, are housed within a Stevenson Screen. The time taken for air to be exchanged from the outside environment to within the screen provides a further time integration for the measurement of the ambient air temperature.

JM: Noted.

4. The response time of the sensor used in the Bureau AWSs is as long or longer than the changes in the temperature of the air it is measuring.

JM: This may be the case. But the key issue has always been achieving consistency with measurements from the mercury thermometers – so there are no discontinuities in the temperature record with the transition from mercury thermometers to temperature probes. There was 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.

5. This means that each one second temperature value is not an instantaneous measurement of the air temperature but an average of the previous 40 to 80 seconds. This process is comparable to the observation process of an observer using a “mercury-in-glass” thermometer. Are these methods consistent with international best practice?

JM: The two claims made in this dot point are not consistent with published studies. As regards ‘these methods’, if this is an attempt at justifying an instantaneous one-second reading, then the answer is: No. .

[Please also note the information as a postscript from Lance Pidgeon – scroll down to after the photograph of us both at Goulburn.]

6. The Bureau’s procedures comply with the World Meteorological Organization’s Guide to Meteorological Instruments and Methods of Observation (the CIMO Guide) WMO-No. 8 (2014 edition). The guide is available here.

JM: The guide at the said link clearly states on page 540 (Part 2, Section 1.3.2.4) that atmospheric air temperature be reported as 1 to 10 minute averages. Therefore, the Bureau’s procedures are not compliant with WMO guidelines.

7. The guide recommends that temperatures be integrated over time to smooth out rapid fluctuations. There is more than one method of achieving this. The WMO guidelines do not prescribe which method to take. In its automatic weather stations the Bureau achieves this by using platinum resistance thermometers. These are comparable to mercury in glass thermometers.

JM: No. The guide clearly states that readings from platinum resistance thermometers are not comparable with instant one-second readings from mercury in glass thermometers.

In summary, given the Bureau is taking one-second extrema, rather than following its own published guidelines (Instruments and Observing Methods Report No. 65, WMO/TD No. 862) recordings taken by the Bureau over the last twenty years from automatic weather stations across Australia may not be fit for purpose. In particular, temperature measurements from Australia since at least 1990 have not been recorded consistent with calibration, and therefore are likely to be invalid?

Jennifer Marohasy
11 September 2017 – 9pm

This advice is also provided as a PDF here: FAST FACTS -Refuted-V2

Jennifer Marohasy and Lance Pidgeon at the Goulburn AWS in early August 2017. Photograph courtesy of The Australian newspaper.

Comment from Lance follows as an important postscript

Following the link provided in the ‘Fast Facts’, I found this:

“It is recommended that the time constant, defined as the time required by the thermometer to register 63.2% of a step change in air temperature, should be 20 s. The time constant depends on the airflow over the sensor.”

This is a completely different thing to the sampling rate and averaging. It is describing the conditions BEFORE the one second sample rate not after.

This time, specifies the curve which is not an average. To compare an exponential decay curve to an average is wrong. If the curve time was over 60 seconds then the most recent would have most of the influence while the oldest would only have the influence of three timeconstants (63 percent of 63 percent of 63 percent).

A rule of thumb is that about 5 time constants need to pass before a reasonable measurement can be taken and 7 or more for an accurate measurment.

So is the BoM also trying to hide that this (before the averaging) time constant is also too short by confusing 5, 7 and 1 time constants as “40 to 80”?

Also, I just noticed that the standard calibration method looks to remove and ignore the noise during the procedure. In particular:

“Since the measurement instrument is an integral part of the electrical thermometer, its calibration may be checked by substituting the resistance thermometer by an accurate decade resistance box and by applying resistances equivalent to fixed 5 K temperature increments over the operational temperature range. The error at any point should not exceed 0.1 K. This work would normally be performed by a servicing technician.”

And with reference again to the ‘Fast Facts’, it is sad that the Bureau do not appear to understand the difference between a thermistor and a platinum resistance thermometer. I write this because the document that Jennifer has posted begins with reference to a ‘thermistor’ and ends with comment about a ‘platinum resistance thermometer’.

Lance Pidgeon
via Crookwell, near Goulburn
12 September 2017 – 8am

*****

As far as I can tell the 2014 document Lance quotes from (which the Bureau claim they are working in accordance with – though clearly they are not) is a someone garbled version of a technically solid report published in 1997, which includes the following advice:

An extract from ‘Instruments and Observing Methods Report No. 65, WMO/TD No. 862’

*****

According to the ‘Fast Facts’, the Bureau’s procedures comply with the World Meteorological Organization’s Guide to Meteorological Instruments and Methods of Observation (the CIMO Guide) WMO-No. 8 (2014 edition). Following are two important extracts from this document:

Uploaded by Jennifer on 14 September 2017 – for future reference.

Filed Under: Information Tagged With: Temperatures

John has Plus 10 Degrees, Bureau Loses Minus 10 Degrees

September 11, 2017 By jennifer

He studied chemistry at Imperial College, London, has 10 degrees, including a law degree, and has published more than 100 scientific papers. I’m referring to my husband, John Abbot. He is also a man of few words.

John Abbot standing in front of the Noosa River, Queensland – not far from the Climate Lab where he works on rainfall forecasting using artificial neural networks.

Last Friday morning, after flipping through the Australian Bureau of Meteorology’s latest 77-page internal report – Review of the Bureau of Meteorology’s Automatic Weather Stations – he looked up at me, and then said, “But this is all about you.”

The report begins by explaining that the Bureau has 695 automatic weather stations spread across Australia, and that data from this network underpins all of the services the Bureau delivers, enabling more than 500,000 public forecasts, and nearly 15,000 weather and ocean warnings which are issued each year. The report then goes on to explain that just two of these weather stations are “not fit for purpose” – Goulburn Airport (Goulburn) and Thredbo Top Station (Thredbo).

On the 5th and 18th July, respectively, I explained in detail at my blog that after temperatures below minus 10 degrees Celsius were measured by the Goulburn and Thredbo weather stations they were not subsequently recorded as such in the appropriate database by the Bureau.

While the Bureau strenuously denied it was setting limits on how cold a temperature could be recorded from any particular weather station, the Minister Josh Frydenberg nevertheless insisted on the review – and of the entire AWS network.

The Minister phoned me late on Thursday, to let me know that the review was done and that the investigation found that Goulburn and Thredbo were the only stations, out of the entire network, where temperature records had been affected.

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. He 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 for that weather station. He then texted me when what appeared to be a new record for July of minus 10.4 was reached, only for us to both see this 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 for the lowest second-readings at one of the stations in the snowfields. Given the weather set-up that morning, I thought it might be cold across that region. 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.

“And I’m vindicated in that 77-page report,” I said to John Abbot – last Friday morning.

But unfortunately, neither the report, nor its recommendations are going to fix the more substantive issues that I have been raising since at least 2011 – when much of the city of Brisbane was flooded by emergency releases from a dam that was never meant to ever fill again, according to the best guesses from our Bureau.

Indeed, in the years preceding the flooding of Brisbane the Bureau’s own David Jones, Head of Climate Analysis, was often penning opinion pieces, including for the Sydney Morning Herald, that explained drought was the new norm for Australia. In an email, back in September 2007 he went as far as to say that: “climate change here in Australia is now running so rampant that we don’t need meteorological data to see it.”

Dr Jones could be characterised as a ‘true believer’. He is now the Head of Climate Monitoring and Prediction at the Bureau. Perhaps not surprisingly the Bureau keeps telling us that next year will be hotter than the last and that this last winter was the warmest on record – never mind the record number of frosts being tallied up by farmers across the south east.

For some years every minister responsible for the Bureau has successfully staved-off what must come eventually: a proper public review into the operations of this institution, which has lost its way. For some years, ministers responsible for the Bureau have been claiming that there can be no external review because there is a need to maintain public confidence – they seem to know that a transparent review and public confidence are incompatible.

The report pertaining to this latest internal review claims that even though there has been a strict limit on how cold temperatures could actually be recorded at Thredbo, Australia’s climate history has in no way been compromised. This is nonsense!

Since the year the new automatic weather station was installed at Thredbo – by coincidence the year my friend Diane died in the landslide – there has been a significant reduction in the number of days measuring minus 10 degrees or lower.

To be clear, and contrary to what is written in this latest report from the internal review, the equipment installed at Thredbo back in 1997 is world class. There is nothing wrong with the equipment, and it can record temperatures down to minus 60 degrees Celsius.

The problem is senior management at the Bureau, and specifically their instructions for how the equipment is to be operated.

For example, and to raise another issue: because the electronic probes in the new automatic weather stations are much more sensitive to temperature change than the previous liquid-in-glass thermometers, the one-second measurements from the new probes must be averaged over 1 to 10 minutes before taking a recording. This is detailed in various reports and is also World Meteorological Organisation policy. So, in the UK, the data loggers are set to automatically average over 1 minute; in the US, it is 5 minutes.

The Bureau has the correct documentation in place, with the key report – based on detailed experimental work undertaken here in Australia in the early 1990s – published back in 1997. But the Bureau is not actually following its own guidelines.

I have worked this out by comparing readings from different pages as displayed on the Bureau’s website. But according to the new internal review of AWS operations, this must stop. In particular, the review found, “the current data flow architecture creates situations where data can be delivered to, and displayed on, the Bureau’s website via multiple pathways and this can be potentially inconsistent and confusing for end users.”

I was initially confused but then treated the various anomalies from the perspective of a puzzle to be solved.

This new report does clarify many issues. Indeed, while I initially thought that the new limit of -10.0 degrees Celsius had just been put in place this winter – it is apparent from the report that it has been in place at Thredbo for ten years, since 2007. What is not clear is how a value that is measured below minus 10 by the equipment is actually recorded, with my observations suggesting that at Thredbo it ends up as blank, while at Goulburn it is rounded to minus 10.0.

Thredbo is not far from the peak of Australia’s highest mountain, Mt Kosciusko. Temperatures have been recorded at Thredbo since January 1966. On six separate days in 1968 temperatures dropped to -10 or below. On 23rd June 1968 temperatures dropped to -11.6. On 28th, 29th and 30th July of that year temperatures of -10.3, -10.6 and -10.1 were recorded. On 28 July 1980, a record low minus 14.7 was recorded. In July 1994, which was an exceptionally cold winter, minus 13.6 was recorded. Not far from Thredbo, at Charlotte Pass in June 1994, the all-time lowest minimum in Australia of minus 23 degrees Celsius was recorded.

During June and July of this year, blizzard conditions were experienced across the Australian Alps, but we will never know how cold it actually got. Because a MSI1 card reader prevented the equipment – able to record down to minus 60 – from recording below minus 10 at Thredbo and probably also at many other locations. It is also impossible to know how cold this last winter was relative to 1994 because the weather station at Charlotte Pass was closed in March 2015 – it is no longer in operation.

Earlier this year, specifically on Wednesday 26 July, I was interviewed by Alan Jones on radio 2GB. He has one of the highest rating talkback radio programs in Australia. From about 7.40 a.m. that morning we discussed my concerns, specifically about limits on how cold temperatures can be recorded at Thredbo.

According to the new internal report from the Bureau, and apparently by coincidence, the very next day, on 27 July the limits were lifted at Thredbo. After 10 years at least, the Thredbo weather station was able to record very low temperatures again.

‘Low’and behold: on 2 August, a minimum temperature of -10.9 was recorded at Thredbo.

It had been such a long time since such a cold temperature had been recorded at Thredbo – at least 15 years coincident with the installation of the card that prevented the measurement of temperatures below minus 10.4.

Rather than announce the lifting of the ban on very cold temperatures at Thredbo, that very same day, 2 August 2017, the Bureau announced that July 2017 had been the warmest on record – ever, for Australia.

Contrary to the Minister’s press release of last Thursday, core issues at the Thredbo weather station have not been fixed – and these are issues that also affect the other 694 weather stations. By its own admission in the report (page 22), the Bureau is recording one-second extrema from at all weather stations: it is not averaging these values over at least one minute as is standard practice in the UK, or over 5 minutes as is done in the US.

Recording one-second extrema (rather than averaging) will bias the minima downwards, and the maxima upwards. Except that the Bureau has been placing limits on how cold an individual weather station can record a temperature, so most of the bias will have been upwards over the last few years – in accordance with Dr Jones’ favourite story about man-made warming.

It is well and truly time for an open, transparent and independent external review of the Bureau, and its management.

And John Abbot would prefer that it wasn’t just about me. So, such a review would need to address the multitude of other issues that have been documented over the years including by Warwick Hughes, Ken Stewart, Joanne Nova, Maurice Newman and indeed also by John Abbot – most recently in the journal Atmospheric Research (volume 197, page 290) where he explains that the Bureau’s probabilistic seasonal rainfall forecasts are misleading.

****
A version of this article was first published at The Spectator Australia.

Filed Under: Information Tagged With: People, Temperatures

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Jennifer Marohasy Jennifer Marohasy BSc PhD has worked in industry and government. She is currently researching a novel technique for long-range weather forecasting funded by the B. Macfie Family Foundation. Read more

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