To Aspirate or Not to Aspirate.

Guest Post by Dr Eric Huxter.

Dr Eric Huxter has been a teacher and researcher of Earth Science for over 40 years. His published doctoral thesis is available here. Eric states in his introductory biography:

“I have been intrigued by the growth in alarmism over climate change and its dominance of public policy.

Given the definition of climate (climate normal) as the mean state of the atmosphere in a region calculated from 30 years of data there is no doubt that climates over the earth change and do so over scales of twice climate normal to millennia. From our understanding of the past it is clear that these changes occur as a series of natural cycles of different frequencies and length.

It is now received wisdom that humans have broken the supremacy of natural climate change.

This blog is designed to investigate aspects of the loose (frayed) ends left by fixating on carbon dioxide.”

I publish below the first of two excellent reports from this must read Blog https://frayedendsblog.wordpress.com/

To Aspirate or Not To Aspirate?

As already discussed on this blog the Meteorological Office has over the past 35 years undergone a programme of replacing manually read Liquid in Glass Thermometers (LIGTs), 0.1°C precision, with continuously recording Platinum Resistance Thermometers (PRTs), 0.01°C (±0.02-0.05°C) precision.

The World Meteorological Organisation CIMO Guide (WMO-No. 8, §2.1.3.3) specifies a 60 s averaging interval for PRT readings but in the WMO Technical Regulations Manual on Codes (WMO-No. 306) it states that while a 1 min averaging period is the minimum and most suitable, averaging periods of up to 10 min are acceptable. I apologise for stating in earlier posts that 5 minutes was recommended by the WMO. This specification is designed to pick up step changes in air temperature within 20 seconds, a measurement impossible with traditional LIGTs. With PRT technology we are measured enhanced details in air temperature which have not been measurable before through greater temporal and thermal precision.

The time constant (response time) of PRTS is far shorter than LIGTs as shown by Burt & de Podesta (2020).

and the Transient response bias of PRTs is clear, especially under low wind conditions. The 3 m.s-1 assumes an aspirated screen.

The PRTs are housed in Stevenson Screens, as LIGTs, but they are more susceptible to the Aitken effect and the fact that 99.99% of airflow is below the assumed minimum (Burt 2020). The Meteorological Office does not routinely use aspirated screens.

Without access to the 1 minute averaged raw data from the Meteorological Offices Synoptic & Climatic network the easiest source of temperature data is from weatherobs.com which generates generally hourly, but shorter intervals from some stations, weather data including the 1min average temperature at that time. However we have no indication of the variability between the hours.

Monitoring UK maximum Daily Temperature as published by the Meteorological Office on its ‘Extreme’ page and its ‘X’ feed, and weatherobs.com, allows a data base to be compiled of daily Maxima and a record of hourly changes from that station, and I have taken 0900 – 1800 readings. Until recently the Meteorological Office enquiries desk had been very helpful in supplying the exact time the record temperature was logged, but they have gone quiet over the past two weeks.{Ed note: exactly my experience} From this information the ‘spike’ in temperature from the previous hour (if known) or from the maximum 1 minute average on the hour can be calculated. This has allowed ‘spikey’ comments to be blogged or ‘X’d.

The real question is how far these short term spikes are recording the ‘true’ meteorological signal and how far they are thermal noise from the Aitken effect, low ventilation rates and local heat sources. To study this I am very grateful to Ray Sanders for introducing me to the data feed from the University of Hull weather station via the Meteorological Office WOW page. The University rates this site as CIMO 4 but it is an aspirated station with 5 minute average, which will provide an excellent baseline for identifying the ‘true’ meteorological signal, allowing for its CIMO class. Conveniently there is a Meteorological Office Synoptic & Climate weather station at Hull East Park, at a similar altitude 5km to the ESE.

Since Ray drew my attention to this happy pairing, in early June, I have tried to collate the data from both sites. The University site is easy since it holds a complete record of its data, the weatherobs.com only holds the past 7 days, therefore I have missed some of the Hull East Park readings. Given that the University reports every 5 minutes and East Park every hour only the on the hour readings from the University have been used for comparability. Whilst there is data drop from my inefficiency it is also worth commenting on the data drop from these sensors. When tabulated dropped data times are ignored which makes processing these data trickier than it ought to be.

We can therefore plot the temperature from the two stations.

What’s not to like, they look pretty much the same and while there is some variation it is, in Climate Science parlance, ‘not by much’ so why worry?

Unpacking this variation suggests that there is a systematic bias in the non-aspirated station. For each day with data from both sites the hourly maximum and minimum temperatures, and hence the daily mean, can be extracted. If the non-aspirated station reflected the ‘true’ meteorological signal we would expect an even distribution of each station being above or below the other’s recorded temperature. However this is not the case.

East Park consistently records higher temperatures than the University, with more higher minimum temperatures.

Over the data set the East Park site averages 0.2°C warmer with greater extremes. This systematic effect will have a distinct impact on Records and Trends, given that 86.6% of the UK’s Synoptic & Climate network are CIMO class 3/4/5.

It is therefore not too much of a stretch to suggest that much of the apparent warming over the past 50 years, especially with the acceleration of warming in the 1990s, is the result of the Meteorological Office progressively replacing LIGTS with PRTs in poorly sited stations, which over record the actual temperatures. The apparent increase is greatest in minimum temperatures, but these data show more impact on these temperatures. It can therefore he postulated that we have two separate populations of temperature records, those from LIGTs and those from PRTs, the result of ‘inhomogeneities’ (Burt & de Podesta 2020) in the temperature records which have a greater impact on the maximum and minimum temperatures.

This can be seen at the global scale:

The lack of curiosity in what we are actually measuring and how it relates to what we used to measure is worrying. As Burt & Podesta (2020) report the meteorological studies of LIGT or PRT time constants is ‘rather scant’ and this suggests that confirmation bias is at work, ‘we know it is warming, we know why it is warming and PRTs tell us it is warming’. Far reaching public policy is being based on this fundamental scientific failing.

Reference

Burt S & de Podesta M, 2020. Response times of meteorological air temperature sensors. Quarterly Journal of the Royal Meteorological Society 146:731 pp. 2789-2800

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As a codicil I would also like to add my personal thanks to Hull University SuDSLab for their very professional and scientific assistance they freely offered me, a stark contrast to the Met Office attitude. An interesting you tube clip about them.

https://www.youtube.com/watch?v=q5k_ZQcEoVw

A second equally illuminating further guest post by Eric will follow further demonstrating “spikiness” and the misinformation induced by Met Office teleology.

Source: https://tallbloke.wordpress.com/2025/08/01/to-aspirate-or-not-to-aspirate/