Posts Tagged ‘Diurnal Temperature Range’

ACORN updated, but not improved. Result: the same bogus data.

March 14, 2015

Early this month the ACORN-SAT dataset was updated to 31 December 2014.  A quick check shows that despite much public criticism, nothing has changed since March 2012 when it was first released.  There have been no corrections.

There are still thousands of days of missing data.

There are still gross errors.

Adjustments remain, and so still have the effect of making many individual sites LESS comparable with neighbours, and of making national trends much greater than those for raw data.

However, in this post I am merely focussing on one of the many erroneous features in Acorn, that of the instances of minimum temperatures exceeding maximum temperatures.

Why bring this up again, as it was first spotted in 2012?  Because it is more evidence of unjustified adjustments, and Acorn’s authors have done nothing about it.

Although a specific check for errors in recording raw maxima and minima was conducted before homogenising, this check could not have been done with the homogenised data. It might be claimed that this feature is normal and due to a cold change arriving after 9.00 a.m.  This would be especially evident in winter at high altitudes such as at Cabramurra, with 212 occurrences.  If so, it would have been evident in the raw data.  However, a check of 22 of the sites, comprising 84% of the instances (803 of 954) reveals there are NO instances of maximum less than minimum in the raw data for Cabramurra, or anywhere else.  All instances occur in the adjusted data.

Fig. 1: Min > Max in Acorn (803 of 954 instances)

 minmax Aust

 Fig. 2: The same test for raw data at the same sites as Fig. 1

minmax Aust raw

 Further, despite the Bureau being aware of the problem since at least 1 July 2013 when Blair Trewin, lead author of ACORN, assured readers of the blog Open Mind (sic) at that “in the next version of the data set (later this year), in cases where the adjusted max < adjusted min, we’ll set both the max and min equal to the mean of the two” (which merely hides the fault caused by adjustments), the problem still exists- 212 occurrences are still in the ACORN record for Cabramurra, and there are 954 in total.  Trewin has done nothing about it- mainly because he would have to redo the whole dataset to do it properly.  The problem exists because adjustments have been too vigorous and too erratic.  The algorithm produces bogus data.  Merely averaging maxima and minima on those 954 days hides the underlying problem.

Here is one example, the worst I have found, (circled in Fig. 1), from Alice Springs, 15 June 1932.

Fig. 3: Raw vs Acorn at Alice Springs

Alice june32

Notice there are NO adjustments in Acorn to raw maxima, but Acorn minima mostly runs along one or two degrees less than raw- except on 1 and 2 June and most notably on 15 June, when Acorn minima shoots to 4.8 degrees above the maxima for the day!  This is caused by an adjustment of 6.4 degrees to the raw temperature.  The Bureau lists the following sites as neighbours used for this adjustment:  Boulia, Tibooburra, and Tennant Creek.  Ignore for the moment that these are all hundreds of kilometres from The Alice, just visually compare their data.

Fig. 4:  Alice vs ‘neighbours’

Alice june32 v neighbours

Tennant Creek and Boulia, hundreds of kilometres north and northeast, are usually several degrees warmer than The Alice, except when Acorn makes those huge adjustments.  Which is the outlier?

This Alice Springs instance is a rogue adjustment due to a leading “1” being inserted; 18.1 entered instead of 8.1.  This is not uncommon in Acorn and crops up repeatedly.

While this is annoying and farcical, it can be easily explained and easily fixed.  The real problem is with data that is not so grossly erroneous, such as at Cabramurra.  This graph shows raw minima and maxima for May and June 1962.  Note that often maximum is not much above minimum: there is little room for error.

Fig. 5: Cabramurra raw

raw Cabramurra

But see what happens with adjustments.

Fig. 6: Cabramurra raw and adjusted

raw vs adjusted Cabramurra

Maxima have been adjusted down, minima up, without any thought for the consequences, so four times in May and June 1962 minima exceed maxima.  Merely averaging maxima and minima for those days will hide the symptom of the underlying disease.  The adjustments cannot be justified because they result in nonsense data.  Exactly how do you explain negative Diurnal Temperature Range?

The problem of a tiny percentage of the record featuring this error is not minor:  it indicates that many adjustments are too great, and also that no quality assurance checks have been performed, and therefore many other types of errors are likely to exist.  And they do.

Now how is it that my laptop can find these errors, whereas the Bureau’s supercomputer can’t?

Here is the full list of sites and instances of bogus data:

Station, Number of days with minimum temperature exceeding the maximum temperature.
Adelaide, 1. Albany, 2. Alice Springs, 36. Birdsville, 1. Bourke, 12. Burketown, 6. Cabramurra, 212. Cairns, 2. Canberra, 4. Cape Borda, 4. Cape Leeuwin, 2. Cape Otway Lighthouse, 63. Charleville, 30. Charters Towers, 8. Dubbo, 8. Esperance, 1. Eucla, 5. Forrest, 1. Gabo Island, 1. Gayndah, 3. Georgetown, 15. Giles, 3. Grove, 1. Halls Creek, 21. Hobart, 7. Inverell, 11. Kalgoorlie-Boulder, 11. Kalumburu, 1. Katanning, 1. Kerang, 1. Kyancutta, 2. Larapuna (Eddystone Point), 4. Longreach, 24. Low Head, 39. Mackay, 61. Marble Bar, 11. Marree, 2. Meekatharra, 12. Melbourne Regional Office, 7. Merredin, 1. Mildura, 1. Miles, 5. Morawa, 7. Moree, 3. Mount Gambier, 12. Nhill, 4. Normanton, 3. Nowra, 2. Orbost, 48. Palmerville, 1. Port Hedland, 2. Port Lincoln, 8. Rabbit Flat, 3. Richmond (NSW), 1. Richmond (Qld), 9. Robe, 2. St George, 2. Sydney, 12. Tarcoola, 4. Tennant Creek, 40. Thargomindah, 5. Tibooburra, 15. Wagga Wagga, 1. Walgett, 3. Wilcannia, 1. Wilsons Promontory, 79. Wittenoom, 4. Wyalong, 2. Yamba, 1.

(From Willis Eschenbach at . Butlers Gorge has a further 37 days.)

Here is a plot of their occurrence- the big lump after 1960 is due to Cabramurra.

Fig. 7: Running 365 day count of min > max (803 of 954)

count incl cabramurra

Australian DTR – the Regional Context

January 12, 2014

I’ve been banging on about DTR in Australia for a while, showing that as an indicator of greenhouse warming, decreasing DTR trend has been lacking from Australian records for some time, such that the trend is flat since 1947.


DTR is Diurnal Temperature Range, the difference between Minimum and Maximum temperature daily.  Several previous posts discuss this.  Greenhouse gases slow back radiation, and thus night time temperatures are expected to be warmer than normal, and minima are expected to increase faster than maxima, so DTR should decrease.

Fig.1: Australian DTR anomalies, 1947 – 2013dtr1947-2013

I’ll now show what is happening on a regional basis.  This map shows the main meteorological regions of Australia.

Fig. 2: The regions.summer1213 regions

The main difference is between Northern Australia and Southern Australia.

Fig.3:  Northern Australian DTR anomalies, 1971 – 2013dtr nth oz 71-2013

43 years of flat trend in DTR!

Fig.4: Southern Australian DTR anomalies, 1938 – 2013dtr sth oz

76 years!

Fig. 5:  South-Western Australian DTR anomalies, 1941 – 2013dtr sw aus

73 years.  But the real eye opener is South Eastern Australia:

Fig. 6: South-Eastern Australian DTR anomalies, 1934 – 2013dtr se aus

That’s right, in South-East Australia, the DTR trend has been flat for 80 years!

Decreasing DTR as a “fingerprint” of greenhouse warming was championed by the 2004 paper by Dr Karl Braganza,

“Diurnal temperature range as an index of global climate change during the twentieth century” Karl Braganza, School of Mathematical Sciences, Monash University, Clayton, Victoria, Australia; David J. Karoly, School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA; J. M. Arblaster, National Center for Atmospheric Research (NCAR), Boulder, Colorado, USA

Braganza et. al. analysed global DTR from 1951 to 2000, finding a significant decline of ~0.4 degrees C.  If we compare Australian data for the same period we find this is corroborated.

Fig. 7:  Australian DTR anomalies 1951 – 2000dtr oz 51-2000

The observed decrease over this period is ~0.35  – 0.4 C.

With the benefit of an extra 13 years of data, we can check whether this continues to be the case.

Fig. 8:  Australian DTR anomalies 1951 – 2013dtr oz 51-2013

What a difference a few years make.

No Evidence of Greenhouse Warming for 67 Years!

January 8, 2014

The release of 2013 data by the BOM has provided me with plenty to work on.  Various commentators are busily alarming people by claiming that the hottest year on record is an indication that global warming due to the enhanced greenhouse effect is already impacting Australia.  What is most disappointing is that the BOM has done nothing to report the truth: that while Australia has definitely been warming, and breaking records, the data show no evidence of greenhouse warming.

One of the key indicators of warming uniquely associated with the enhanced greenhouse effect is night time temperatures (minima) increasing faster than daytime temperatures (maxima).  The difference between the two is called the Diurnal Temperature Range, or DTR.  So, decreasing DTR would be evidence of greenhouse warming.

Here is Australian DTR since 1947:dtr1947-2013

That’s dead flat or slightly rising for 67 years!

I couldn’t believe it either, and double checked.  There’s no mistake- DTR shows no evidence of greenhouse warming in Australia, with a flat trend for 67 years.