Mercury thermometers versus probes in computerized climate stations – so extra watts?

From Jennifer Marohasy’s blog.

Jennifer Marohassi

Tuesday, April 18 at 9:30 p.m. Pacific Time

Wednesday 19 April at 2.30pm Australian Eastern Standard Time

Listen online:

The Australian Bureau of Meteorology has replaced most of its mercury thermometers in automatic weather stations with platinum resistance probes.

My assessment of almost twenty years of parallel data from Mildura and only three years of parallel data from Brisbane Airport shows that the probes can record both hotter and colder than the mercury, but are not equivalent.

Statisticians are notorious for disagreeing on the most appropriate statistical test, but should at least state the name of the test performed and the level of significance, as an attorney would detail the case law referred to.

The Bureau claims an assessment of the full 2019-2022 period for Brisbane Airport found no statistically significant difference between the probe and the mercury thermometer. But without giving any information.

More generally, their climate scientist, Blair Trewin, claims that the parallel data — temperature series recorded with a mercury thermometer and a platinum RTD probe at the same locations and at the same time — don’t differ significantly across their network of about 700 automatic weather stations, but that’s as far as I can tell can judge, there is only parallel data for 38 locations.

My analysis of Brisbane Airport’s three-year parallel data – only recently made available after years of wrangling over an FOI request with the Bureau – shows that the probe is recording hotter than the mercury 41% of the time, and 26% of the time Cooler. The difference is statistically significant (paired t-test, n=1094, p<0.05).

The differences are not random and there is a clear discontinuity after December 2019.

I initially thought that this jump from an average monthly difference of minus 0.28°C in December 2019 to plus 0.11 in January 2020 (a difference of almost 0.4°C) represented a recalibration of the probe.

The Bureau has denied this, saying there was a fault in the automatic weather station which was fixed immediately and has been operating within specifications as of January 2020. After January 2020, the probe may record up to 0.7°C warmer.

I have requested that all parallel data be released, starting with requests for data from Wilsons Promontory lighthouse in 2015.

In 2011, a panel of experts commented that the Bureau’s “guidelines” have allowed a tolerance of ±0.5°C for field testing of either in-glass (mercury) or RTD (probes) thermometers for the past 100 years, and this out For this reason, the Panel did not classify the Australian Panel’s monitoring practices as international best practice.

It is time for another expert assessment and for the release of all parallel Bureau data. There will be a total of 15 years of parallel data for Brisbane Airport and a similar amount for another 37 of the Bureau’s 700 official weather stations.

I’ll be speaking to the legendary Chris Smith on TNT radio this afternoon on these issues.

Tuesday, April 18 at 9:30 p.m. Pacific Time

Wednesday 19 April at 2.30pm Australian Eastern Standard Time

Listen online:

So far, the Bureau has given a variety of reasons for not releasing the parallel data. In the case of the Brisbane airport data, she initially claimed that manually scanning the handwritten A8 report was too tedious. When John Abbot’s FOI request landed with the Information Commissioner, the Bureau, somewhat bizarrely, claimed that the parallel data for Brisbane Airport did not exist.

While the bureau provided me with nearly 10,000 scanned A8 reports for Mildura following the intervention of then Environment Secretary Josh Frydenberg in 2017, the bureau continues to withhold a few key pages relating to September 2012.

I can only estimate the likely differences between the probe and a mercury for the month of September at Mildura until these parallel data are released. In the meantime, the Bureau stands by its claim that the temperature of 37.7°C recorded by the probe in Mildura on September 22, 2017 is a new hottest record dating back to 1889, although temperatures at the time coincided with other devices recorded, with a mercury thermometer.

An A8 report showing the manually recorded temperatures of the mercury and also the probe at Brisbane Airport on October 15, 2021.

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