date: Tue, 21 Jan 97 06:53:51 EST
from: drdendro@lamont.ldgo.columbia.edu (edward cook)
subject: Que pasa?
to: k.briffa@uea.ac.uk


Hi Keith,

I was just wondering how you are making out with that Kalman filter mess
I sent you. I am only going to be around for about 2 more weeks before I
go downunder. So, if you have anything you want to pass by me, it ought
to be before then. In my conversations with Brendan, it has occurred to
me that something analogous to what you find in your data (a systematic
departure between tree rings and temperature over the past few decades)
also is apparent in some of the Huon pine data. Specifically, the BCH
site of Brendan's, which is the second highest site compared to Lake
Johnston, shows the same effect as you see, at least in the ring widths
anyway. We don't yet have density data for that site. The high-pass
variations in ring width lock in beautifully with temperature, better in
fact than does Lake Johnston. However, the low-pass side goes down over
the past 30 years years as temperatures have increased. Brendan and I
have speculated about this a lot. My pet theory is that temperatures
have risen sufficiently to cause net photosynthesis to go into deficit
occasionally (i.e. respiration exceeds primary photosynthesis). Of
course, this theory is pretty bad as is because it doesn't explain why
the slightly higher (say 50m) Lake Johnston site maintains its temperature
response at all frequencies. I suppose it is arguable that what we are
seeing is a very sharply defined threshold response and the LJH site is
just cold enough to escape this effect. There also appears to be an
inversion layer over western Tasmania that kicks in at around 900m. I
don't know. Maybe it is totally coincidental.

Cheers,

Ed