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ACORN-SAT weather station audit

Western Australia raw temperature audit of BoM ACORN-SAT stations


In March 2012, the Bureau of Meteorology introduced a new dataset called ACORN-SAT which supersedes the High Quality network to estimate Australia's historic temperature trends.

The ACORN-SAT station dataset discards the Western Australia High Quality stations Cape Naturaliste, Derby, Jarrahwood, Kellerberrin, Newman, Roebourne, Rottnest, Southern Cross and York, replacing them with the WA weather stations at Cunderdin, Dalwallinu, Eucla, Forrest, Kalumburu, Learmonth, Morawa and Wittenoom.

Within a technical report released in conjunction with the new dataset, the BoM states that metrication and rounding of degrees added approximately .1C to temperatures in a 10 year test spanning five years before and after 1972.

The report states that a series of La Nina oscillations, record rainfall and cloud cover cooled the Australian climate from 1973 to 1977, potentially masking the full extent of artificial warming from metrication and temperature rounding, and because of uncertainty about this climatic anomaly the bias has not been adjusted within the ACORN-SAT dataset. See extracts from technical report.

Western Australia audit

This audit analyses the fractional proportion of Fahrenheit and Celsius degrees recorded before and after September 1972 metrication, based upon the exact timeframes of temperature data at each of the 47 Western Australia weather station records within the ACORN-SAT dataset since 1910.

Including neighbouring associated weather stations used by the BoM to homogenise temperature trends over time, the 47 WA weather stations are audited in this presentation to determine their distribution of Fahrenheit and Celsius fractions before and after Australian temperature metrication on 1 September 1972.

In total, the ACORN-SAT dataset includes 885,496 minimum and maximum Fahrenheit temperatures recorded at 35 WA weather stations before September 1972 and 756,809 minimum and maximum Celsius temperatures recorded at 38 stations from 1 September 1972 to 31 December 2011, totalling 1,642,305 recordings.

The 26 HQ and weather stations in Western Australia previously gauged by the BoM comprised 1,066,506 daily Fahrenheit temperatures recorded before September 1972 and 871,617 Celsius temperatures recorded since metrication to 31 December 2011, totalling 1,938,123 recordings.

Note: there is evidence that BoM unadjusted raw temperatures were adjusted from the historic records. For example, at Perth Regional Office 9034 in 1940, daily temperatures published by The West Australian newspaper showed annual maxima rounded to the same as BoM raw data but the newspaper's annual minima rounded 0.3C warmer than in the BoM database. This implies that historic minima were warmer than referenced by the BoM so that they appear to have risen more steeply to their current average than was the case. See a monthly comparison of newspaper and raw temperatures (PDF 164kb) or a spreadsheet analysis of the maximum and minimum temperatures (Excel download 61kb) at Perth Regional Office 9034 throughout 1940.


Fahrenheit .0 rounding before 1972

In the pre-72 Fahrenheit era, 27.9% of all temperatures recorded at all 35 WA stations within the ACORN-SAT dataset were recorded as rounded .0F degrees.

This is .3% more rounded .0F than in the audit of 26 WA weather stations in the BoM's previous High Quality temperature series. The combined 29.7% of temperatures recorded as .9F and .1F infers an actual .0F ratio around 45%.


acorn temperature fractions


A breakdown of this data shows that 26.8% of all Fahrenheit maxima recorded before September 1972 were rounded to .0F and 29% of all minima were rounded to .0F.


acorn temperature fractions


The proportions of total converted Celsius fractions recorded at all ACORN-SAT stations before 1 September 1972 were:


acorn temperature fractions


The combined 11.1% proportion of .0C and .5C is identical to the proportion of .0C and .5C converted Celsius recordings before 1972 at the 26 WA stations in the High Quality weather station series.


Celsius .0 rounding after 1972

In the post-72 Celsius era, 16.5% of all temperatures recorded at all 38 WA stations within the ACORN-SAT dataset were recorded as rounded .0C degrees. This is 1.4% less rounded .0Cs than in the audit of 26 WA weather stations in the BoM's previous High Quality temperature series.


acorn celsius fractions


A breakdown of this data shows that 16.2% of all Celsius maxima recorded since September 1972 were rounded to .0F and 16.9% of all minima were rounded to .0F. As with Fahrenheit fractional distribution, this shows a greater tendency for minima rather than maxima to round to .0.


acorn maximum temperature fractions

Among the 76 minimum and maximum temperatures at the 38 WA ACORN-SAT weather stations recording since 1972, 61 had blocks of .0C and .5C over 10 or more consecutive days which contribute much of the high .0C proportion in the Celsius era. The longest block is 594 consecutive days of .0C and .5C minima and maxima recorded at Cape Leeuwin 9518 from 19 May 1998 to 10 January 2003.


New ACORN-SAT station fraction distributions

The eight new WA locations and neighbouring stations in the ACORN-SAT dataset comprise 123,906 minimum and maximum Fahrenheit temperatures recorded at all stations before September 1972 and 221,569 minimum and maximum Celsius temperatures recorded at all stations from 1 September 1972 to 31 December 2011, totalling 345,475 recordings.

In the pre-72 Fahrenheit era, 33.6% of all temperatures recorded at these eight stations were recorded as rounded .0F degrees. The combined 33.7% of temperatures recorded as .9F and .1F infers an actual .0F ratio above 50%.


acorn temperature dataset


In the post-72 Celsius era, 18.5% of all temperatures recorded at these eight stations were recorded as rounded .0C degrees.


acorn weather stations


Fahrenheit and Celsius raw temperature rounding has not influenced the selection of the eight new weather stations in the 2012 ACORN-SET dataset.

Below are examples of rounding from the eight new WA stations:


acorn temperatures in australia


acorn temperatures in eucla


The ACORN-SAT temperature dataset also includes new neighbouring sites at weather stations previously included in the High Quality dataset, including Perth Airport Comparison 9250 below:


perth airport acorn acorn-sat temperatures


Below are the percentages of minimum and maximum whole .0 Fahrenheit recordings before 1972 and whole .0 Celsius recordings since 1972 at each of the 47 WA weather stations in the ACORN-SAT dataset

Click weather station names for audit details


Station Minima .0F % Maxima .0F %
Albany Airport 9741 20.3% 16.6%
Albany 9500 30.4% 29.1%
Bridgetown Comparison 9510 30.7% 31%
Bridgetown 9617 Opened after 1972 Opened after 1972
Broome Airport 3003 18.6% 16.1%
Broome Post Office 3002 31.8% 28.4%
Broome Comparison 3089 Opened after 1972 Opened after 1972
Cape Leeuwin 9518 36.9% 34.5%
Carnarvon Airport 6011 17.3% 15.6%
Carnarvon Post Office 6062 29.7% 25.4%
Cunderdin Airfield 10286 Opened after 1972 Opened after 1972
Cunderdin 10035 25.9% 22.5%
Dalwallinu Comparison 8039 33.6% 28.5%
Dalwallinu 8297 Opened after 1972 Opened after 1972
Esperance 9789 16.2% 14.9%
Esperance Post Office 9541 30.7% 28.3%
Eucla 11003 46.5% 45.9%
Forrest 11052 Opened after 1972 Opened after 1972
Forrest Aero 11004 15.8% 13.9%
Geraldton Airport Comparison 8051 17.7% 14.9%
Geraldton Town 8050 27.7% 26.5%
Giles Meteorolgical Office 13017 16.8% 14.3%
Halls Creek Airport 2012 21.5% 17.2%
Old Halls Creek 2011 27.9% 26.5%
Halls Creek Comparison 2071 Opened after 1972 Opened after 1972
Kalgoorlie-Boulder Airport 12038 17.9% 16.4%
Kalgoorlie Post Office 12039 22.8% 22.7%
Kalumburu 1019 Opened after 1972 Opened after 1972
Kalumburu Mission 1021 20.6% 22.6%
Katanning Comparison 10579 34.2% 32%
Katanning 10916 Opened after 1972 Opened after 1972
Learmonth Airport 5007 Opened after 1972 Opened after 1972
Marble Bar Comparison 4020 39% 34.5%
Marble Bar 4106 Opened after 1972 Opened after 1972
Meekatharra Airport 7045 17.8% 16%
Meekatharra Post Office 7046 42.8% 38.3%
Meekatharra Milos AWS Comparison 7204 Opened after 1972 Opened after 1972
Merredin 10092 27.4% 26.5%
Merredin Research Station 10093 17.6% 15.5%
Morawa Airport 8296 Opened after 1972 Opened after 1972
Morawa 8093 51.9% 51.6%
Perth Airport 9021 16.1% 13.2%
Perth Regional Office 9034 17.1% 13.7%
Perth Airport Comparison 9250 Opened after 1972 Opened after 1972
Port Hedland Airport 4032 15.5% 13.7%
Port Hedland PO 4002 40.3% 37.3%
Port Hedland Milos AWS Comparison 4104 Opened after 1972 Opened after 1972
Wandering 10917 Opened after 1972 Opened after 1972
Wandering Comparison 10648 36.8% 36%
Wittenoom 5026 41.9% 39%



The full audit results for all Western Australia weather stations in the start and end timelines of the ACORN-SAT dataset are within:


The full audit results for all Western Australia ACORN-SAT weather stations including all station records, including before 1910, are within:


The full audit results for only the new Western Australia ACORN-SAT and associated weather stations are within:




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