Monday, June 18, 2012

5304.txt

date: Mon, 22 Sep 2003 12:54:13 -0700
from: "Malcolm Hughes" <mhughesatXYZxyzr.arizona.edu>
subject: Re: western US trees data
to: Keith Briffa <k.briffaatXYZxyz.ac.uk>

Dear Keith - sorry to have taken so long to reply. After a somewhat disrupted
summer, the beginning of the semester was made all the more messy by my
computer getting seriously "wormed". I'll answer your questions as best I can.
1) As you didn't say, I assume that the western chronologies of interest are those
used in Mann et al 1999. As the paper says, the first 3 PCs of these were used in
that paper. Going back to the original files, I found 27 chronologies from the
western US that reached back to AD 1000 of further at the time that work was
done. I attach 3 MS Excel files that give some details of them, including the
ITRDB identifiers, which is what Mike used to get the chronologies. The Excel
files are abstracted from the many huge files Richard Holmes built for me
during that seasrch of the ITRDB, so each will contain stuff that may be
irrelevant:
vchron11000 contains, inter alia, the ITRDB ID, species code, first year, last
year, collector's name
vchron41000 contains the ITRDB IDm then the first and last years with 5, 10,
etc samples
vchron81000 contains the ID, etc and then in the following cols: V mn
sensitivity W chronology autocorrelation, AE number of series, AG mean
correlation of series with chronology AH mean series autocorrelation, AI seores
mean length, seires median segment length.
Please remember that this set ranges from lower forest border to upper forest
border, so that various mixtures from all precip to precip plus temp locally
apply.

2) I have no idea of Mike and Phil used - I assume it was the PCs of those in this
subset that go back to AD1, but I wasn't involved in any way, so I don't know.
3) As for Gordon's series - the MBH 99 paper says which one was used, but it
never passed through my hands - Mike dealt with this.
4) I don't know what alternative standardization methods you had in mind, but
you should be aware that it would be completely unjustified to assume that the
first measured ring was anywhere near the pith in many of these sites, especially
as you go back in time, where the chronologies are based on remnants that have
weathered on the inside and the outside. For this, and related, reasons, it would
also be completely unjustified to assume any constant, or small, distance in
years of the first measured rings from pith. That is, I can see no way of making a
remotely reliable estimate of cambial age in the vast majority of these samples. I
am sitting on the bones of a manuscript in which I had someone spend several
months checking many hundreds of bristlecone and similar cross-sections and
cores in our store. They found only a few dozen - less than 10%, were either pith
was present, or the innermost ring could reasonbly be described as 'near pith' . I
have another manuscript in a slightly better state of preparation where we
restandardized many of these series in the following way - identify the long,
flat part of the smaple ringwidth curve (i.e. remove the 'grand period of growth',
if present) and then fit a straight line of no or negative slope.
5) Of course, I'd be happy to collaborate - what did you have in mind?
How are you doing these days?
Cheers, Malcolm
>
> Dear Malcolm
> just sending this again in case you did not get it last time (last
> month) cheers Keith
>
> Malcolm
> I am exploring the role of the tree-ring data in the various
> reconstructions of Northern Hemisphere temperatures , particularly ,
> as you know, the issue of standardisation of the original data and the
> relative influence of specific chronologies on the estimates of
> uncertainty relating to the reconstructions. I am anxious to
> understand the fine details of the role of the "western US trees " and
> the "correction" applied (by comparison with Gordon's Northern tree
> line data . Can you point me to the detailed information on what
> constitutes the western tree-ring data , as used in Mann et al and
> Mann and Jones (in press) , and to where we can pick these up to redo
> some of the analyses on them (ditto the Jacoby data). We wish to try
> alternative standardisation of both sets and explore the robustness of
> the long-term trends etc. Of course I would be happy if yo would
> collaborate with us on this. Cheers Keith
>
> --
> Professor Keith Briffa,
> Climatic Research Unit
> University of East Anglia
> Norwich, NR4 7TJ, U.K.
>
> Phone: +44-1603-593909
> Fax: +44-1603-507784
>
> http://www.cru.uea.ac.uk/cru/people/briffa/
>

Malcolm Hughes
Professor of Dendrochronology
Laboratory of Tree-Ring Research
University of Arizona
Tucson, AZ 85721
520-621-6470
fax 520-621-8229

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