The Adelaide temperature history has been discussed at Jo Nova’s – Forgotten: Historic hot temperatures recorded with detail and care in Adelaide –
First – Adelaide weather data was collected at West Terrace for around a century then in Feb 1977 a new site commenced 3.2km away at Kent Town. The new BoM adjusted ACORN SAT data is named Adelaide – there is a downloadable ACORN SAT station catalogue if you go to the TAB ‘Data and network’ at the above link.
I wanted to make a start showing how the daily ACORN SAT (Australian Climate Observations Reference Network – Surface Air Temperature) adjustments vary from day to day – seemingly inexplicably. Interesting patterns appear – interesting results emerge – the reasons for which I can only speculate on.
ACORN used West Terrace data till Kent Town started Feb 1977. Then ACORN used Kent Town minimum untouched from Feb 1977. However ACORN adjusted the Kent Town max Feb 1977 until end 2001. West Terrace closed end Feb 1979. The overlap period 1977-1979 for West Terrace and Kent Town showed the raw minimums differed over a greater range than the max diffs.
Here are the daily ACORN minus West Terrace adjustments 1910-Feb 1977 – Three interesting step changes in the minimum adjustments are seen circa 1943-1951 and 1961 – were there site changes?
This Table shows daily details for Jan 1939 – month of record max at time of the 1939 bushfires – now the Adelaide all-time highest max of 46.1 on 12 Jan magically becomes 46.4 according to the god-like BoM.
Here is an example of ACORN producing seven outlier cold nights in April 1960.
Kent Town 23090 max was adjusted to end of 2001 in ACORN – Looking at ACORN max minus Ken Town max we see that mostly the adjustments make ACORN warmer except for a period ~1983-1990 where the adjustments are more balanced either side of zero. Were there site changes ~1983 and 1990?
If the steps are due to Kent Town site changes – then this should have affected the minimums – but ACORN does not touch the Kent Town minimums.
For those interested to pore through spreadsheets –
[1] ACORN has minimum on 16 April 1961 at 5.8 yet no other station in District 23A went that low.
[2] April 1970 example of mystery missing minimums in ACORN on 5th and 27th – what was wrong with the West Terrace data ? Or is it related to those days being slightly warm peaks. An example of many ACORN mysteries.
It is not uncommon for ACORN to reject a days data for no apparent reason. There are many examples of ACORN missing out an extra day if West Terrace misses a day eg Jan and Jul 1913.
[3] In May 1972 from 4th to 10th ACORN makes no adjustments to a string of warm nights where West Terrace is usually the warmest night site in district 23A. This puzzles me – I can understand that the minimums at West Terrace are often too warm and I thought ACORN was tweaking these down so I ask – why this string of zero adjustments to a run of standout warm nights. Is this an indication that the ACORN algorithm was fully up to quota in May 1972? A contra result like this leaves me puzzled.
I am sure readers can come up with many ACORN puzzles.