(If this post comes to the attention of Met Eireann before I have emailed directly about this – apologies, I’m just back from an arctic ski and aurora spotting trip, and this post is in part a gathering together of material for that direct email. I had written at length before departure, but spotted further details requiring extensive revision. The revised email will be with you shortly)
This post is not yet completed, but is being made a public post now to make the two images here available immediately as I have found that when I add images to comments made at other blogs such images fail to appear in those comments. I will complete the post in the next day or two.
There is a further delay in completing this post as the laptop with work in progress is temporarily out of service until the cooling fan is replaced, hopefully back February 17th.
I will add links to the data at the Met Eireann website to enable verification that the data is as shown above, and that corruption is not confined to 2013 to 2016, and not confined to this one station.
The Met Eireann most recent four year monthly data can be found at Monthly Data
The longer (not necessarily full length record however) data can be found at Historical Data (I’ll return to add navigation advice here when I have completed other sections of this post. Navigation on this section of the Met Eireann site may not be intuitively obvious)
The GHCN-M version used above was ghcnm.tavg.v184.108.40.20661230.qcu.dat (which of course had not had a December 2016 value added, whereas Met Eireann calculates and shows a month-to-date mean, 7.4°C up to December 30th)
As shown below, the correct 2013 values were shown by GHCN-M for a time in 2013, corrupted for a time later in 2013, and briefly reappeared again in 2014, before settling down again as corrupted values.
Now follow the history of the April 2013 value (7.4°C according to Met Eireann). In the first GHCN-M file below (dated May 19th 2013) it is correctly recorded, and attributed to a CLIMAT report as source (740 P). This value is the most recent value to reach GHCN-M, and in this case the CLIMAT report has been correctly decoded. I will return to this question of correct or incorrect decoding of CLIMAT reports below).
By July 9th the still correct value has as data source “received by the UK Met Office” (740 K). This has been the usual change of data source, first CLIMAT report, then the UK Met Office. As seen on May 19th the March 2013 value had already been processed in this way (430 K).
On (or before) the 8th November the data source changed to “Monthly Climatic Data of the World (MCDW) QC completed but value is not yet published” (1040 WC). The value had now become the rogue value 10.4°C. the “W” quality flag indicates “monthly value is duplicated from the previous month, based upon regional and spatial criteria”. My experience of my region would suggest that duplicating the mean temperature of the previous month would very rarely produce a correct estimate for the following month. What “regional and spatial criteria” have required the replacement of a recorded monthly mean my a rogue value?
After that this rogue value has been retained, except for a brief return to the correct value and UK Met Office as source on (and possibly around) June 28th 2014. In mid 2015 the data source changed to “Final (Published) Monthly Climatic Data of the World (MCDW)”.
Each monthly value above is followed by either one or two letters. A single letter, or the second of two letters, gives the data source:
|C = Monthly Climatic Data of the World (MCDW) QC completed but value is not yet published|
|K = received by the UK Met Office|
|M = Final (Published) Monthly Climatic Data of the World (MCDW)|
|P = CLIMAT (Data transmitted over the GTS, not yet fully processed for the MCDW)|
|W = World Weather Records (WWR), 9th series 1991 through 2000|
The first letter of two letters is a quality control flag:
|S = monthly value has failed spatial consistency check. Any value found to be between 2.5 and 5.0 bi-weight standard deviations from the bi-weight mean, is more closely scrutinized by examining the 5 closest neighbors (not to exceed 500.0 km) and determine their associated distribution of respective z-scores. At least one of the neighbor stations must have a z score with the same sign as the target and its z-score must be greater than or equal to the z-score listed in column B, where column B is expressed as a function of the target z-score ranges (column A). See GHCN-M README for table.|
|W = monthly value is duplicated from the previous month, based upon regional and spatial criteria and is only applied from the year 2000 to the present.|
to be added
As noted above, the April 2013 value for Cork Airport was initially decoded correctly from a CLIMAT report. But this correct decoding has not always been the case.
When Valentia Observatory (62103953000) became an AWS station in April 2012 the first April values entering GHCN-M from decoded CLIMAT reports were rogue values