Lentran DCNN0579 – More on the issues of distorted sites and instrumentation shortcomings.

XXXXXXXXXXXXXXXXXXXXXXXXXXX Above Image from 2005 XXXXXXXXXXXXXXXXXXXXXXXXXXXXX

57.45953 -4.37322 Met Office CIMO Assessed Class 4 Installed 1/1/1974 XXXAbove image 2024.XXXX

It is rather obvious where the gist of this review is going from the above two images nearly 20 years apart. There are however other issues to discuss here than just this deterioration of this site that probably only a chain saw can fix.

Lentran was installed in 1974 just over 5 miles to the west of Inverness in an open exposed area known as “The Aird” at the small hamlet of Newton Hill. The site is not flat but not unacceptably steep and would possibly have made a reasonable Class 2 on original installation. I do not know who is responsible in these situations for the surrounding area but somewhat frustratingly (as is so often the case) trees have been allowed to grow and the site is now subject to deep shade and a major windbreak from the south around to west. The site is now assessed as Class 4 with its associated inaccuracy and the value of its relatively long term record is reduced accordingly.

From installation to June 2009 the site was manually reporting whereupon it was deemed worthy to be automated. Again typical of so many other locations the 21st century observations record was starting to become unreliable with, for example, in 2007 only 267 days of accurate readings taken. It is worth noting that when such manual sites are automated, the instrumentation also changes from a Liquid in Glass thermometer (LIGT) to an Electrical Resistance Thermometer (ERT) model typically a Platinum Resistance Thermometer (PRT). The potential effects of this change are worth repeating.

The very high quality Met Office LIGT is manufactured for longevity and accurately calibrated ( and subsequently retested regularly) to a precise standard. The standard accuracy has a 0.2°C tolerance. Temperature instruments have a quoted “response time” which is a measure of how quickly they react to a predetermined percentage (typically either 63% or 95%) of the final temperature and also dependent on the surrounding medium i.e gas or liguid. With LIGTs this rate is also dependent on the construction of the unit with larger bulb and thicker glass units responding more slowly. Met Office larger more durable LIGTs are quoted as having response times of 60 to 70 seconds for 63% of final temperature in air at 3 metres per second velocity.

With PRTs the readings are interpreted from the variable electrical resistance through platinum wire or foil changing with temperature. The tolerance of PRTs is quoted as 0.01°C. PRTs are much faster reacting with the Met Office standard platinum foil Vaisala PTU series being quoted at approximately 20 seconds for 63% in air at the same velocity as above. 95% of final value is often achieved well under 40 seconds. PRTs offer continuous readings typically by the second which requires period averaging to give a stable figure. The World Meteorological Organisation (WMO) recommends 5 minute averaging for PRTs to give a figure likely more in line with the slower response of LIGTs , however, the UK Met Office works on only 1 minute averaging. They offer no explanation for not meeting WMO recommendation. Also notable is that this deriving an arithmetic mean (i.e. 60 x seconds readings added then divided by 60) can result in means being quoted to the 5th decimal place and far beyond their actual accuracy. As ex Met Office manager John Maynard commented “ A perfect example of this was the Met Office site where temperatures were recorded to 4 or 5 decimal places, giving the readings the sense of extreme accuracy, whereas they just showed the stupidity of the observer. “

A second factor to note with both instrument types is the quoted dependency on a set air speed minimum. Failure to meet this requirement can cause over-recording due to known problems with the design of Stevenson Screens first identified by meteorologist James Aitken in the same year that such screen types were almost universally adopted in 1884 and named after him – Aitken Effect. Stevenson Screens are known to trap stagnant air at low wind speeds which can then either overheat in sunshine or alternatively retain daytime accrued warmth overnight. This in turn renders the thermometers to further over record in the lower than design standard air flow. This effect can often be very transient and whilst picked up by the fast reacting modern PRT was far less likely to have been recorded by a LIGT. Former Met office manager John Maynard noted this fast reacting phenomenon very succinctly in his post stating”

“For example a site on an airport may present no problems for a MiG {LIGT} the quicker response of the Pt may catch a quick burst of an aeroplane’s exhaust as it passes en route for take-off or landing.   This will result in a higher Maximum Temperature recorded for that day. 

Again the WMO offers the recommendation that Stevenson Screens, or any other type of radiation shielding devices, are “artificially aspirated” (fan assisted) to ensure adequate speed of air movement for accuracy of readings. The UK Met Office advised me under Freedom of Information request that it does NOT have any artificially aspirated screens at its weather stations. {I am currently running some comparisons between a known professional institution’s (University of Hull) artificially aspirated device and the nearby Met Office (Hull, East Park) junk Class 5 site – the latter regularly records significantly warmer}

Pause for thought on these points…….What observational science can you think of that would still use a known defective measuring system that is over 140 years old? What observational science would put latter 20th Century technology into a Victorian casing?

Jules Verne published ” From the Earth to the Moon: A Direct Route in 97 Hours, 20 Minutes” one year after Civil Engineer Thomas Stevenson originally designed his now famous instrumentation screen. Would all those latter 20th century Apollo astronauts have been happy to get on board a Jules Verne era designed rocket? I really doubt that so how can the Met Office justify mis-using modern instrumentation in such antiquated screen systems against all expert meteorological advice? This is a typical professional use aspirated screen as deployed by https://www.sudslab.co.uk/

Referring back to Lentran, this is a prime example of very many other sites I have so far reviewed. Originally an LIGT in an open site (likely Class 2) it would have rarely experienced low wind speeds causing any relevant level of temperature elevation. Unchecked tree growth has now created a wind break effect thereby increasing incidence of low wind speed and enhancing Aitken effect. Subsequently the instrumentation has been changed (but not the antiquated casing) to a much more rapidly responding temperature sensor that is equally more likely to react to the transient elevating effects. The temperature uplift is inevitable.

Alternatively, the Met Office could have established controlled areas, free from any unnatural effects, UHI or extraneous heat sources and fitted it with modern effective radiation shielded equipment with artificial aspiration to ensure readings accuracy…….. so why haven’t they? Every other science moves forward, it’s called progress except for the oxymoron that is “climate science”.

Source: https://tallbloke.wordpress.com/2025/06/28/lentran-dcnn0579-more-on-the-issues-of-distorted-sites-and-instrumentation-shortcomings/