ACORN-SAT 2: Eucla: The Devil in the detail

I’m having a break from looking at Acorn 2 data from Queensland.  I’ve been wondering:  what’s going on?  What’s beneath these changes?  In particular, I was struck by statements in the accompanying Research Paper that

In total, there were 966 adjustments applied in version 2 of the ACORN-SAT dataset, 463 for maximum temperature and 503 for minimum temperature.”

The Bureau is referring to breakpoints in the data where adjustments are applied to all previous years.  In the daily data, there are tens of thousands of adjustments at each station.

For example, in Eucla’s Tmax record, there are 34,145 daily datapoints; 34,144 in Acorn 1; and 33,858 in Acorn 2.  There are  10,190 instances where Acorn 1 makes no change to raw data, and 9,312 in Acorn 2.  Most of the instances of no adjustments are since 1995.  Before then almost every day has been adjusted.

And the devil is in the detail.

The following plots show how adjustments are applied to the range of raw maxima.  First Acorn 1.

Figure 1:  Acorn 1 adjustments as applied to raw maxima at Eucla

Ac1 raw adj

Figure 2:  Acorn 2 adjustments as applied to raw maxima

Ac2 raw adj

Acorn 2 removes the large negative adjustments for temperatures in the high 30s, and the spread is wider for very high temperatures.  So far so good.

Figure 3 shows where many of these adjustments are made.

Figure 3:  Acorn 2 and  raw maxima

Eucla 1913-2017

Between 1930 and 1995 many high temperature spikes are reduced by 5 degrees and more.

For example, here is November 1960.

Figure 4:  Raw, Acorn 1, and Acorn 2 in November 1960

Eucla Nov 1960

The Bureau can truthfully claim that there is a balance between positive and negative adjustments.

However, note how all temperatures over 35C have been reduced by five degrees.  This is common across these years.

Perhaps temperatures on very hot days at Eucla in the 1960s were exaggerated?  Perhaps they were not read accurately?

If this pattern of hot day reductions is generally followed at stations across large regions, e.g. southern Australia, the effect will be that climate analysis based on Acorn 2 will show that past extremes were generally not as high as nowadays.

And that can’t be a bad thing for the meme.

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10 Responses to “ACORN-SAT 2: Eucla: The Devil in the detail”

  1. trevor prowse Says:

    why are early data reduced for correcting industrial heating in the later data?. I have asked some friends which way they would adjust data and they say ,” add the effect of the industrial effect by raising the early data”. Is that`s why Australia is experiencing the hottest ever January?—trevor

    • kenskingdom Says:

      Because (currrently) our temperatures are supposed to be accurate, a reliable trend or pattern can only be constructed by making past data “look like” they would be if observed now. In other words, what the past looks like relative to the present. So if we think there has been a recent warming influence, past data are warmed. The big arguments are: how is the change detected? when did it happen? and how adjustments should be made. A steady rise should not be corrected by a one size fits all adjustment to all previous data.

  2. Ian George Says:

    It is definitely getting worse. For instance –
    Bourke, Jan 1939 – max average temp for the month.
    AWAP (raw) temp average = 40.4C.
    ACORN 1 average = 40.03C.
    ACORN 2 average = 39.9C.
    Again, all the temps above 30C have been reduced and all the temps below 30C have been increased.
    BoM’s even-handedness?

    Can’t wait for ACORN 3.

  3. Brian Gunter Says:

    Ken, A few years ago (in 2014), regarding ACORN-SAT 1, I came across details of the stations used to adjust the temperatures at each ACORN-SAT station. Some of these were hundreds of kms away and in different climatic zones.

    Is such information available for the ACORN-SAT 2 adjustments? If so could you please tell me how I can locate such information. This could be interesting for Eucla which does not have many nearby stations – I wonder if BOM used Albany and Alice Springs to remove any apparent inconsistencies in the Eucla raw data?

  4. David Brewer Says:

    What gets me is, how on earth can they, with a straight face, adjust records by so much?

    Who on earth would believe that Eucla’s maximum temperature on 20 November 1960, recorded on the day as 77 degrees Fahrenheit, was actually 85 degrees Fahrenheit?

    Ken I also love your Figure 3. Before adjustments – no trend, flat as a board, a perfect illustration of the null hypothesis being confirmed. After adjustment, a massive dip in maximum temperatures from the 1930s to the 1980s, yet no movement in minimum temperatures over the same period – a result that lacks any physical plausibility.

    And Eucla is one of the most remote stations in one of the smallest settlements in the world, the last place one would expect to need adjustments, let alone this sort of brutal shoving around.

    Has the BoM responded in any way to the criticisms on this and other sites?

  5. Bill in Oz Says:

    Ken I have been looking at your analysis of the BOM’s ACORN 2.
    I hope that you will do some work on South Australia as per ACORN 2.

    I will be attending a public meeting in late March here in SA. The guest speaker is from the BOM. It would be good to be able to ask him what the hell the BOM is doing with SA weather station data.


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