There's always something. This time it's over USHCN, in 2013 in Luling, Texas. And yes, I've been arguing. But it's actually quite interesting.
It started, as it seems to lately, with Steven Goddard, who has a new name. Paul Homewood joined in the excitement and looked into Luling, which he says is the first thing he came across. His posts are (here and here). And an account that is actually very helpful from tchannon.
The basic story is that in 2013 USHCN discarded the raw data from Luling, a Coop station in Texas, and replaced it with infill from neighbouring stations. That is the standard response to missing data. But the excitement was that the raw data was there and was quite a lot cooler. Here is the table that he calls "shocking":
Update: mesoman notes in a comment below that there was a cable fault which caused low temperature readings which was repaired on Jan 14th 2014. Looks like problem solved. The system did the right thing.
|Bias Adjusted |
There are nowadays lots of sources of information. All USHCN stations are now GHCN too, so you can look at the GHCN details. They don't help much. Paul linked the metadata, which I'll refer to. There are some other tabs there which may help.
An alternative account which is well worth checking is BEST, which I noted at WUWT and Paul's. It includes this useful plot of the difference between raw values and the regional average:
Note the recent dive and the red markings, which are what BEST understands to be station moves.
This starts to look like an explanation. A station move followed by a marked cooling relative to the region is exactly what homogenization is about. And if the program believes there was a move which changed things, then the right thing to do is exactly to replace the data with a regional estimate until there is enough history to estimate the effect of the change.
Paul posted an update, noting that the metadata did show a change of coordinates at that time, but with a note to say that no equipment had moved. They were just improving the accuracy. Still, it's quite likely that the computer program took the change as confirmation of the inhomogeneity of the sudden dip.
Blogger tchannon found lots of useful information at the site of the Foundation Farm which hosts the station. He noted some equipment issues which he thought might have triggered the computer's response.
If there wasn't an actual move, the sudden dip at Luling doesn't have a clear explanation. It's real, though. GHCN has the same raw data, and you can see my shaded plot of it here. These are plots of anomalies, which I have calculated as described here. The shaded anomaly plot is actually a very good way to spot issues with data, as I describe in that post and some of its links.
I have extracted some of the key months here. The extreme of Paul's table above was October, and here is what my plot shows:
The black dots are stations with data. The deep blue dip is Luling. It is a clear outlier. On my plot you can shift-click for details and it shows the anomaly of -2.80°C. Not coincidentally, this lines up with the -3.95°C in Paul's table (I took the extreme case).
Here are some plots of other months. In each case the blue dip id Luling:
July 2013 Anomaly=-0.95°C
Sept 2013 Anomaly=-1.08°C
Dec 2013 Anomaly=-2.52°C
Dec 2012 Anomaly=2.31°C
November looks extreme, but it was a cold month everywhere there. I've included December 2012 to show that it does seem to be a recent issue that arose some time in 2013. Making the pics is a bit tedious, so I'll leave it there, but you can make your own here.
So something seems to be going on at Luling; it's not just a computer glitch.