I’m finally trying to finalize my presentation on Jones et al  for the US GCRP workshop in November, which is necessarily mostly about the Polar Urals and Tornetrask reconstructions. Bot MXD chronologies and RW chronologies are supposed to correlate to temperature. So an obvious quesiton is how do they correlate to eachother. I’ve plotted scatter plots up separately before. Here I present them together with some color coding to show key dates.
The figure below shows scatter plots for RW chronology against MXD chronology (both RCS versions, both my calculations) for Polar Urals and Tornetrask. The Polar Urals chronology incorporates the 1999 update from russ176.
Figure 1. Scatter Plot RW chronology versus MXD chronology. Red – 20th Cent; blue- 19th Cent; green – other.
The individual distributions of RW and MXD are not normal, but it’s particular easy to see that the combined distribution is not bivariate normal. At Polar Urals, other than a tail towards the origin for low values, there seems to be relatively little relationship between MXD and RW values, with MXD values seeming to max out, while there is much greater upwards variation in RW values. There seems to be a "tail" towards the origin, with 19th century values over-represented in the tail. Here’s another example which I posted up before here:
Jaemtland RQ and MXD distributions
The form of bivariate distribution between RW and MXD seems to be surprisingly characteristic. I’ve been browsing the literature on copula functions to think about methods of representing this type of distribution, but I don’t know how to do it at present and the dendro community doesn’t even seem to have noticed the problem. It’s hard to see how both RW and MXD chronologies can have a strong relationship to temperature and still generate this type of joint distribution.
A calibration-exercise involving the 19th century will give more weight to the transition from the tail to the body of values than is justified by the data overall, making the relationships seem better than they really are. There are also a lot of values outside the range of the calibration period.
The differences at Tornetrask are odd. At Polar Urals, the calibration-verification period values seem to be a little to the high left of the body of values, while at Tornetrask they seem to be a little to the lower right.
The "Briffa Adjustment" at Tornetrask (see here) was an arbitrary upward adjustment of MXD values in the 20th century because the MXD chronology was lower than the RW chronology. But the MXD values look very much in a plausible range, hardly arguing for any "adjustment". Or it would be just as plausible to adjust the MXD values for Polar Urals downwards in the 20th century.