Hello everyone - I've been a regular user of netweather for years for info gathering, but am newbie registered now as I recently found out about this topic (HADCET adjustment) and came across this thread. Thanks for all the useful comments above. I have seen a number of people plot the changes in a linear fashion, but I found it helpful to plot things in a heatmap (done below for the mean).
All I can say is that that's an odd set of adjustments. Feb, July and August get the majority of the post 2006 upgrades; June essentially untouched, apart from one of the biggest upgrades in 2005. Last three months of the year get the heavy downgrades 1974 through to 2000. The wobbles start suddenly in 1974 (what did the three day week effects anyone?!!)...
As others have pointed out, Zero adjustments between 1917 and 1967. Then nine adjustments between 1853 and 1916 Then nothing back to 1659 except for five trivial tweaks 1788 to 1798.
Spreadsheet available if anyone wants to cross-check.
I'd welcome any comments or suggestions for further research.
