Archive for March, 2019

ACORN-SAT 2.0: South Australia- Science Fiction

March 28, 2019

This is the fourth in a series of posts in which I directly compare the most recent version of Australia’s temperature record, ACORN-SAT 2, with that of the previous version, ACORN-SAT 1.  Daily data are directly downloaded from the Bureau of Meteorology. I do not analyse against raw data (available at Climate Data Online), except for particular examples, as I am interested in how different Acorn 2 is from Acorn 1.  The basis for the new version is in the Research Report.

See my previous posts for Western Australia, the Northern Territory and Queensland for a general introduction.

The Context – South Australia

Figure 1 is a map of Australia showing all of the Bureau’s ACORN-SAT climate monitoring stations.  South Australia has a narrow band of arable country in the south with cool wet winters and hot dry summers, but most of the state is desert.  South Australia achieved notoriety 18 months ago when the whole state endured an electricity blackout- but of course large scale adoption of renewable energy was blameless.

Figure 1:  Australian ACORN-SAT stations

SA map

There are thirteen Acorn stations in the South Australian BOM database.  Differences between Acorn 1 and Acorn 2 are summarized in the following sections.

Largest temperature differences

In maxima, changes to Acorn 1 daily data ranged from +9.7 ℃ in 1996 to -7.6 ℃ in 1993 at Port Lincoln, with changes of +8.5 ℃ on many occasions, applied to individual daily figures.

Figure 2:  Daily changes in maxima from Acorn 1 to Acorn 2 at Port Lincoln

PortLincoln diffs max

Minima adjustments ranged from -5.5 ℃ again at Port Lincoln to +9.1 ℃ at Snowtown, and there were many other large adjustments at other stations as well.  Most changes were small but numerous, for example at Mount Gambier where the changes to Acorn 1 ranged between -2.2 ℃ and +0.5 ℃ for many years.

Figure 3:  Daily changes in minima from Acorn 1 to Acorn 2 at Mount Gambier:

MtGambier diffs min

(Remember, these are adjustments to Acorn 1, which was supposed to be “world’s best practice” seven years ago.  How did the Bureau get it so wrong the first time?  Has world’s best practice changed so much in seven years?)

Record temperatures

Most stations had their record highs actually reduced.  New record maxima were established at two stations, Port Lincoln increased from 46.7 ℃ to 47.9 ℃, and Oodnadatta set a new record of 51.1 degrees Celsius, which is a new record for all of Australia, pipping Carnarvon in WA by 0.1 ℃.

Figure 4:  New version of maxima at Oodnadatta December 1959 – January 1960

Oodnadatta record max

New record low temperatures were established at Cape Borda, Nuriootpa, and Mount Gambier.  Mount Gambier shows the Bureau at its silliest:

Figure 5:  Three versions of minima at Mt Gambier June 1950

MtGambier record min

Acorn version 1 had warmed the minima by 0.4 ℃, but version 2 cools version 1 by 0.6 ℃, making it cooler than the raw figures.

Up, down- what was the ‘correct’ temperature?.

Quality Control: especially minimum temperatures higher than maximum.

In Acorn 1, eight out of the thirteen stations had at least one example of minimum higher than maximum.  Blair Trewin claims he has “fixed” this problem (which he concedes was “physically unrealistic”) by adjusting temperatures in Acorn 2 so that the maximum and minimum are the same, so that DTR for the day is zero.  In his words:

A procedure was therefore adopted under which, if a day had a negative diurnal range in the adjusted data, the maximum and minimum temperatures were each corrected to the mean of the original adjusted maximum and adjusted minimum, creating no change in the daily mean.

That is how he “corrected” the worst South Australian example in Acorn 1 (minimum 2.4 ℃ above maximum at Tarcoola).  Here is a plot of the raw data and changes made by Acorn 1 and Acorn 2 at Tarcoola from 26 April to 5 May 1923.

Figure 6:  Tarcoola temperatures 26 April – 5 May 1923

Tarcoola DTR

Acorn 1 maxima (orange line) were slightly reduced below Raw (brown). Acorn 1 minima (grey) were far above raw minima (light blue).  Result: garbage.  Acorn 2 has made minima (dark blue) about two degrees less than Acorn 1.

The problem was caused by far too large adjustments, as Figure 7 shows:

Figure 7:  Adjustments to raw Tarcoola minima 26 April – 5 May 1923

Tarcoola adjustments

Acorn 1 adjustments to raw minima were as much as 4.4 degrees; Acorn 2 has introduced variety- sometimes lower, sometimes higher.

Figure 8 shows the effect Acorn adjustments have on annual temperature trends.

Figure 8:  Trends in Tarcoola minima 1922-2017

Tarcoola min ann trends

I spliced the old Tarcoola record with Tarcoola Aero which overlapped  from 1998 to 2000 to create a “minimally adjusted” series, shown in blue.  This series is cooling at -0.46 ℃ per 100 years.  Acorn 1 reversed this trend, showing warming at 0.67 ℃ per 100 years, but Acorn 2 has increased the Acorn 1 trend more than three times to +2.43 ℃ per 100 years.


There are no additional stations, so the network is still extremely sparse.

There is no more additional digitized data.

Large differences between Acorn 1 and Acorn 2 daily data of several degrees Celsius are found at Port Lincoln, Snowtown, Tarcoola, and Mount Gambier.

A new Australian record maximum temperature has been set at 51.1 ℃ at Oodnadatta, Port Lincoln also has a new record, but other locations had record maxima reduced.  New record low temperatures were established at Cape Borda, Nuriootpa, and Mount Gambier.

The issue of instances of minima being higher than maxima caused by too vigorous adjustments has been “fixed” by arbitrary adjustments.

Excessive adjustments have resulted in Tarcoola’s raw minima trend of -0.46℃ per 100 years being changed to +0.67 ℃ in Acorn 1 and an incredible +2.43 ℃ in Acorn 2, an increase of 262% over Acorn 1.

The size of the adjustments only seven years after the “world’s best practice” dataset was launched, is incredible, and demands explanation.

Acorn 2’s adjustments are science fiction.

Next up: Tasmania.