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ACORN-SAT weather station audit Western Australia raw temperature audit of BoM ACORN-SAT stations
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.
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%.
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.
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.
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%.
Below are examples of rounding from the eight new WA stations:
Click weather station names for audit details
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