Photo above: Kalgoorlie, Western Australia, circa 1930
Author: Dr. Michael Chase
This post looks at monthly averages of daily maximum temperatures recorded at Kalgoorlie, and surrounding areas, in the inter-war years of 1920-40, during which ACORN-SAT makes two adjustments. The validity of the adjustments is discussed, as well as their wider significance for other Australian weather station data.
First of all here is a clear example of a temperature inhomogeneity at Kalgoorlie Post Office (black curve), suddenly changing its temperature relative to nearby Menzies (mauve) in 1936:
The ACORN-SAT adjustment summary gives “Move” as the explanation for its temperature adjustments (decreases) at Kalgoorlie, for all years prior to 1936. It is the “all years before 1936” part of the adjustments that is in serious doubt, because the appendix to Simon Torok’s PhD thesis gives the reason for the move:
The thermometers and screen were moved a mere 100 yards in 1936 because of sheds, and it seems likely that the resulting drop in temperature was caused by the removal of the thermometers from the heat trap created by the sheds, rather than by any intrinsic difference in temperature between the new and old locations. Temperature changes due to location are persistent and justify the adjustment of all temperatures prior to the move, but temperature changes due to sheds is probably transient in nature, and correction should only be applied to (say) 1910 data if there is evidence that the shed heat trap was in place then, which seems unlikely.
The station history summary shown above gives a flavour of the problems involved in measuring temperatures in the inter-war years (such as readings taken by girls!), worth bearing in mind in the discussion below of the possible inhomogeneity in 1930, which I think is in doubt. Note that central organisation probably improved accuracy overall, but it tended to make changes happen all at about the same time, for example all three stations mentioned above had some sort of change in 1935/36, which makes it difficult to deal with inhomogeneities around that time.
The following figure shows the data at Kalgoorlie Post Office around 1930, together with eye-ball estimates of averages before and after:
ACORN-SAT says that there was a non-climatic drop in Tmax temperatures at Kalgoorlie in 1930, but I find the evidence for it unconvincing. Firstly there is no mention of any change in the station history summary at that time, and secondly the local (well-inland only) neighbours don’t show anything unusual at Kalgoorlie at that time:
The figure above shows a cooling trend amongst all the stations (the well-inland ones only) in the area, but bear in mind potential screen problems, which may have distorted the trend if there were more sunny years before 1930 than after.
ACORN-SAT calculates the size of its temperature adjustments from how temperatures changed at neighbouring stations, but most of the neighbours used are closer to the sea than Kalgoorlie, hence have a greater maritime moderating effect on any temperature trend. There are hints in the data that around 1930 Kalgoorlie was much more in an inland weather pattern than in that of the stations with strong maritime influence.
I think that there is currently a respectable hypothesis that around 1930 Kalgoorlie was cooling in Tmax, and maybe the especially cool year of 1931 (and its aftermath) triggered the ACORN-SAT detectors to examine it, and they produced an erroneous decision because most of the neighbours were more moderated by the sea to the West and South.
Further work is needed at Kalgoorlie to sort out the uncertainties and produce a more accurate set of temperature adjustments than is provided by ACORN-SAT.