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ACORN 2 influence on Northern Territory temperature trends

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In late 2018 the Australian Bureau of Meteorology provided access to the ACORN 2 daily temperatures (Australian Climate Observations Reference Network - Surface Air Temperatures), which is the bureau's dataset of homogenised or adjusted raw temperatures at 112 Australian weather stations dating back to 1910.

It is assumed that ACORN 2 will replace the ACORN 1 dataset (introduced in 2012) as the historic reference used for comparison of modern temperatures. These are usually presented to the public as temperature anomalies compared to a 1961-90 baseline at each weather station.

There are five ACORN stations in the Northern Territory. This page analyses the daily temperatures at all five weather stations but averages the three with a start year of 1910 to ensure a uniform timescale (although Tennant Creek begins in 1911).

Daily temperatures in ACORN 1, ACORN 2 and RAW have been annualised, and below are charts showing the difference between the two homogenised datasets when compared to their original raw annual temperatures. This analysis only allows the inclusion of years within which there were no months with less than 15 days of recorded temperatures, as is the ACORN protocol.

Three Northern Territory stations begin in 1910 and end in 2017 in ACORN 1, ACORN 2 and RAW - Alice Springs, Darwin and Tennant Creek. The first charts below show maximum and minimum temperature trends at these three stations with associated data that, although not the same as all five ACORN stations across the Northern Territory, suggest the new ACORN 2 dataset has warmed the territory's ACORN 1 maximum by 0.28C and cooled its minimum by 0.01C comparing 1910-1963 with 1964-2017 (first and second halves).

Excel files at the bottom of each station chart and summary can be downloaded to compare how the ACORN 2 algorithms influence daily, monthly and annual temperatures at all five sites since 1910.

acorn 2 northern territory maximum temperatures

1910-1963 - v1 30.34C / v2 30.01C / raw 30.83C

1964-2017 - v1 31.04C / v2 30.99C / raw 31.04C

v1 warmed 0.70C / v2 warmed 0.98C / raw warmed 0.21C

Average change per decade : v1 0.14C / v2 0.20C / raw 0.06C

Northern Territory 2000-2017 - v1 31.29C / v2 31.28C / raw 31.29C

1961-90 - v1 30.80C / v2 - 30.70C / raw 30.82C

Download Excel spreadsheet for three NT weather stations in ACORN 1, ACORN 2 and RAW

acorn 2 northern territory minimum temperatures

1910-1963 - v1 18.21C / v2 17.92C / raw 18.42C

1964-2017 - v1 18.72C / v2 18.42C / raw 18.74C

v1 warmed 0.51C / v2 warmed 0.50C / raw warmed 0.32C

Average change per decade : v1 0.09C / v2 0.09C / raw 0.03C

Northern Territory 2000-2017 - v1 18.79C / v2 18.60C / raw 18.72C

1961-90 - v1 18.51C / v2 - 18.15C / raw 18.61C

Download Excel spreadsheet for three NT weather stations in ACORN 1 and ACORN 2 and RAW

Station menu

Alice Springs, Darwin, Tennant Creek, Rabbit Flat, Victoria River Downs

Alice Springs

acorn 2 alice springs maximum temperatures

1910-1963 - v1 28.05C / v2 28.10C / CDO raw 28.29C

1964-2017 - v1 28.99C / v2 29.24C / CDO raw 28.99C

v1 warmed 0.94C / v2 warmed 1.14C / raw warmed 0.70C

Average change per decade : v1 0.15C / v2 0.20C / raw 0.09C

Alice Springs 2000-2017 - v1 29.45C / v2 29.45C / raw 29.45C (2018 was 30.73C)

1961-90 - v1 28.59C / v2 28.98C / raw 28.59C

Pre 1972 .0 F rounding v1 - 30.62% / v2 - 17.33% / raw - 50.52%

Post 1972 .0 C rounding v1 - 11.35% / v2 - 10.03% / raw - 11.35%

Alice Springs 15540 has annual max temps back to 1879: 1879-1889 + 1891 +1893-1909 = 28.85C

15540 overlap with 15590 1 November 1941 to 31 December 1953 : 15540 28.51C / 15590 28.13C

ACORN catalogue: The original site (015540) was at the Telegraph Station, 3 km north of the town. There is no known documentation of the screen type at the Telegraph Station but the observations are consistent with a Stevenson screen having been used there. The site was enclosed by a rock wall about 1 m high and painted white that would have interrupted wind flow and reflected heat. Observations moved to the Post Office on 23 January 1932. The Post Office site continued until 1953 but data after 1944 were not used in ACORN-SAT as there appear to have been changes at the Post Office site around the time that the airport site opened. Measurements have been taken at the airport (015590) since 1941. There was a site move (550 m east-northeast) in July 1974. An automatic weather station was installed on 21 March 1991 and became the primary instrument on 1 November 1996. The site moved a few metres west on 27 May 2002.

1986-1995 raw max averaged 28.95C and post AWS 1997-2006 averaged 29.49C

Alice Springs max Excel spreadsheets

acorn 2 alice springs minimum temperatures

1910-1963 - v1 12.50C / v2 11.89C / CDO raw 13.09C

1964-2017 - v1 13.13C / v2 12.36C / CDO raw 13.21C

v1 warmed 0.63C / v2 warmed 0.47C / raw warmed 0.12C

Average change per decade : v1 0.09C / v2 0.10C / raw -0.01C

Alice Springs 2000-2017 - v1 13.38C / v2 12.88C / raw 13.18C (2018 was 13.28C)

1961-90 - v1 12.76C / v2 11.86C / raw 13.10C

Pre 1972 .0 F rounding v1 - 18.56% / v2 - 18.39% / raw - 55.25%

Post 1972 .0 C rounding v1 - 10.05% / v2 - 9.76% / raw - 11.55%

Alice Springs 15540 has annual min temps back to 1879: 1879-1902 + 1904-1909 = 12.83C

15540 overlap with 15590 1 November 1941 to 31 December 1953 : 15540 12.46C / 15590 12.86C

1986-1995 raw min averaged 13.68C and post AWS 1997-2006 averaged 13.24C

Alice Springs min Excel spreadsheets

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Darwin

acorn 2 darwin maximum temperatures

1910-1963 - v1 31.46C / v2 31.04C / CDO raw 32.10C

1964-2017 - v1 32.19C / v2 32.08C / CDO raw 32.19C

v1 warmed 0.73C / v2 warmed 1.04C / raw warmed 0.09C

Average change per decade : v1 0.13C / v2 0.18C / raw 0.02C

Darwin 2000-2017 - v1 32.43C / v2 32.42C / raw 32.42C (2018 was 32.82C)

1961-90 - v1 32.02C / v2 31.74C / raw 32.02C

Pre 1972 .0 F rounding v1 - 22.32% / v2 - 18.07% / raw - 32.61%

Post 1972 .0 C rounding v1 - 11.31% / v2 - 9.64% / raw - 11.31%

Darwin 14016 has annual max temps back to 1885: 1885-1909 = 32.97C

14016 overlap with 14015 1 February 1941 to 31 January 1942 : 14016 31.42C / 14015 30.85C

ACORN catalogue: Earlier observations were made at the Post Office (014016), in the central city area. This is on a peninsula in Darwin Harbour which means that the prevailing dry-season southeasterlies have a trajectory over Darwin Harbour (whereas at the airport they are over land). The site deteriorated progressively from the mid-1930s, becoming overshadowed by trees, especially after 1937. The site (along with the remainder of the Post Office) was destroyed in the Japanese air raids of February 1942 and never rebuilt. The airport site (014015) has been operating since February 1941. An automatic weather station was installed on 1 October 1990 and became the primary instrument on 1 November 1996. The site moved about 900 m east (along the southern edge of the airport) on 7 August 2001, with observations at the original site continuing under the station number 014040 until June 2007.

1986-1995 raw max averaged 32.11C and post AWS 1997-2006 averaged 32.23C

Darwin max Excel spreadsheets

acorn 2 darwin minimum temperatures

1910-1963 - v1 22.64C / v2 22.69C / CDO raw 23.39C

1964-2017 - v1 23.24C / v2 23.17C / CDO raw 23.28C

v1 warmed 0.60C / v2 warmed 0.48C / raw cooled 0.11C

Average change per decade : v1 0.08C / v2 0.07C / raw -0.04C

Darwin 2000-2017 - v1 23.17C / v2 23.17C / raw 23.17C (2018 was 23.45C)

1961-90 - v1 23.19C / v2 23.07C / raw 23.29C

Pre 1972 .0 F rounding v1 - 17.75% / v2 - 16.47% / raw - 33.85%

Post 1972 .0 C rounding v1 - 11.67% / v2 - 9.12% / raw - 11.93%

Darwin 14016 has annual min temps back to 1885: 1885-1909 = 23.56C

14016 overlap with 14015 1 February 1941 to 31 January 1942 : 14016 24.20C / 14015 22.67C

1986-1995 raw min averaged 23.60C and post AWS 1997-2006 averaged 23.13C

Darwin min Excel spreadsheets

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Rabbit Flat

acorn 2 rabbit flat maximum temperatures

1970-1994 - v1 33.51C / v2 33.79C / CDO raw 33.46C

1995-2017 - v1 33.86C / v2 33.87C / CDO raw 33.89C

v1 warmed 0.35C / v2 warmed 0.08C / raw warmed 0.43C

Average change per decade : v1 0.21C / v2 0.11C / raw 0.28C

Rabbit Flat 2000-2017 - v1 33.80C / v2 33.80C / raw 33.80C (2018 was 34.98C)

Pre 1972 .0 F rounding v1 - 18.84% / v2 - 17.93% / raw - 22.42%

Post 1972 .0 C rounding v1 - 10.35% / v2 - 10.31% / raw - 12.77%

15548 overlap with 15666 15 November 1996 to 30 November 1998 : 15548 34.42C / 15666 34.10C

ACORN catalogue: The first site (015548) has no indication of any moves between 1969 and 1998 but did become rather overgrown over time. The automatic weather station was installed about 200 m to the west in 1996. The two sites operated in parallel from 1996 to 1998. There is no indication of any moves at the new site.

Assuming the AWS was operational from 1996, 1986-1995 raw max averaged 34.13C and post AWS 1997-2006 averaged 33.71C

Rabbit Flat max Excel spreadsheets

acorn 2 rabbit flat minimum temperatures

1970-1994 - v1 16.31C / v2 16.74C / CDO raw 16.32C

1995-2017 - v1 16.63C / v2 16.69C / CDO raw 16.60C

v1 warmed 0.32C / v2 cooled 0.05C / raw warmed 0.28C

Average change per decade : v1 0.21C / v2 0.15C / raw 0.07C

Rabbit Flat 2000-2017 - v1 16.48C / v2 16.48C / raw 16.48C (2018 was 16.96C)

Pre 1972 .0 F rounding v1 - 18.02% / v2 - 19.03% / raw - 32.92%

Post 1972 .0 C rounding v1 - 10.35% / v2 - 10.47% / raw - 16.39%

15548 overlap with 15666 15 November 1996 to 30 November 1998 : 15548 17.47C / 15666 17.89C

Assuming the AWS was operational from 1996, 1986-1995 raw min averaged 16.37C and post AWS 1997-2006 averaged 16.72C

Rabbit Flat min Excel spreadsheets

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Tennant Creek

acorn 2 tennant creek maximum temperatures

1910-1963 - v1 31.56C / v2 30.92C / CDO raw 32.17C

1964-2017 - v1 31.92C / v2 31.66C / CDO raw 31.92C

v1 warmed 0.36C / v2 warmed 0.74C / raw cooled 0.25C

Average change per decade : v1 0.10C / v2 0.18C / raw 0.05C

Tennant Creek 2000-2017 - v1 31.98C / v2 31.98C / raw 31.98C (2018 was 33.56C)

1961-90 - v1 31.80C / v2 31.40C / raw 31.87C

Pre 1972 .0 F rounding v1 - 19.71% / v2 - 17.05% / raw - 61.79%

Post 1972 .0 C rounding v1 - 11.89% / v2 - 9.79% / raw - 11.89%

15087 overlap with 15135 27 July 1969 to 31 October 1970 : 15087 32.36C / 15135 32.04C

ACORN catalogue: The original site (015087) was based in the town. There was a major move (12 km south) in June 1935 and a smaller move of about 20 m in November 1963. This later site was quite close to a road. New screens were installed to replace damaged ones in May 1945 and November 1958. Observations ceased in 1970. This airport site has been operating since 1969. An automatic weather station was installed on 8 July 1990 and has been the primary instrument since 1 November 1996. There are no known substantial moves at this location.

1986-1995 raw max averaged 32.27C and post AWS 1997-2006 averaged 31.82C

Tennant Creek max Excel spreadsheets

acorn 2 tennant creek minimum temperatures

1910-1963 - v1 19.51C / v2 19.13C / CDO raw 18.72C

1964-2017 - v1 19.76C / v2 19.70C / CDO raw 19.71C

v1 warmed 0.25C / v2 warmed 0.57C / raw warmed 0.99C

Average change per decade : v1 0.08C / v2 0.10C / raw 0.13C

Tennant Creek 2000-2017 - v1 19.82C / v2 19.76C / raw 19.82C (2018 was 20.48C)

1961-90 - v1 19.54C / v2 19.49C / raw 19.42C

Pre 1972 .0 F rounding v1 - 16.05% / v2 - 19.33% / raw - 64.64%

Post 1972 .0 C rounding v1 - 11.96% / v2 - 10.83% / raw - 11.96%

15087 overlap with 15135 25 July 1969 to 31 October 1970 : 15087 18.56C / 15135 18.91C

1986-1995 raw min averaged 20.43C and post AWS 1997-2006 averaged 19.90C

Tennant Creek min Excel spreadsheets

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Victoria River Downs

acorn 2 rabbit flat maximum temperatures

1965-1990 - v1 34.84C / v2 35.07C / CDO raw 34.56C

1991-2017 - v1 34.87C / v2 34.86C / CDO raw 34.43C

v1 warmed 0.03C / v2 cooled 0.21C / raw cooled 0.13C

Average change per decade : v1 0.12C / v2 0.00C / raw 0.03C

Victoria River Downs 2000-2017 - v1 34.78C / v2 34.77C / raw 34.48C (2018 was 35.66C)

Pre 1972 .0 F rounding v1 - 16.79% / v2 - 21.65% / raw - 40.40%

Post 1972 .0 C rounding v1 - 10.19% / v2 - 10.84% / raw - 19.26%

ACORN catalogue: The site moved 250 m northwest in August 1987. An automatic weather station was installed on 9 May 1997. Station photos indicate that the grass was watered up until around 2007; data indicate a marked increase in maximum temperatures around this time, especially during the dry season.

1987-1996 raw max averaged 34.62C and post AWS 1998-2007 averaged 34.07C

Victoria River Downs max Excel spreadsheets

acorn 2 rabbit flat minimum temperatures

1965-1990 - v1 19.97C / v2 19.99C / CDO raw 19.83C

1991-2017 - v1 19.51C / v2 19.58C / CDO raw 19.41C

v1 cooled 0.46C / v2 cooled 0.41C / raw cooled 0.42C

Average change per decade : v1 -0.09C / v2 -0.02C / raw -0.04C

Victoria River Downs 2000-2017 - v1 19.32C / v2 19.32C / raw 19.32C (2018 was 19.41C)

Pre 1972 .0 F rounding v1 - 17.14% / v2 - 18.80% / raw - 49.05%

Post 1972 .0 C rounding v1 - 10.53% / v2 - 11.00% / raw - 18.43%

1987-1996 raw min averaged 19.94C and post AWS 1998-2007 averaged 19.43C

Victoria River Downs min Excel spreadsheets

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