cc: hegerl@duke.edu,t.osborn@uea.ac.uk
date: Tue Oct  8 16:35:17 2002
from: Keith Briffa <k.briffa@uea.ac.uk>
subject: Re: paleo data
to: Phil Jones <p.jones@uea.ac.uk>, Tom Crowley <tcrowley@duke.edu>

   Dear Tom
   after a little detective work we have deduced that the data sent to you constitute a
   version of Northern Hemisphere Land temperatures (april- sept) produced by PCA regression
   using regional average density chronologies (ie the JGR paper you refereed I believe). It
   is true that high frequency component is not in my opinion optimal in describing the
   relative magnitude of extreme inter-annual extremes. This is to do with the unpredictable
   weighting ascribed to certain areas (tree-density series) in the averaging of the original
   raw data ( this is boring and I won't go into it unless you really want me to). THe
   relative differences in year-to-year values are likely better represented in the
   N.Hemisphere series produced by averaging regional series produced using a different
   approach in which the initial data are high-pass filtered and then merged in a more
   straight forward way. This is more equivalent to the series on volcanic signals described
   in our Nature paper, though the low-frequency component in this series is definitely not
   represented. There is another series , that one could consider a good compromise . That is
   a composite of the Age-Banding approach (JGR) low-frequency variance added to the earlier
   (Nature) high-frequency component. We did this for Figure 6 in the JGR paper , but did not
   provide the data on our web site I now realize. However this composite series is VERY
   highly correlated with the "better" high frequency data - see the correlations (Table 1 and
   related text in
   http://www.cru.uea.ac.uk/cru/people/briffa/jgr2001/Briffa2001.pdf
   There are many possible ways of producing a "Northern Hemisphere" average , involving
   different prior regionalisation and secondary weighting (in space and through time) of the
   constituent series) . Non can be considered "correct". If you would like us to dig out the
   composite series or discuss specific aspects of the logic or uncertainties associated with
   the  different large averages let me know. Perhaps it would be better to discuss this on
   the phone? As for longer series , we can provide  the 2000 year N.Eurasian data (a
   composite of ring width chronologies in N.Sweden, The Yamal peninsula, and Taimyr
   or a similar Northern tree-ring chronology incorporating more data eg see
   http://www.cru.uea.ac.uk/cru/people/briffa/qsr1999/
   At 02:29 PM 10/1/02 +0100, Phil Jones wrote:

      Tom,
         Been away and going again tomorrow. Had a chat with Keith and Tim and one of them
      will send a reply and data later this week.
      Cheers
      Phil
     At 11:28 26/09/02 -0400, Tom Crowley wrote:

     Hi Phil,
     thanks for all your help on the bams paper
     DOE is being exceedingly slow in processing the paperwork for our new round - I will
     keep you posted.
     I am also wondering whether we can get some data from you:
     Gabi is comparing our 2d ebm run with the briffa et al 2001 jgr time series in order to
     compare the model prediction of - I think you mentioned at one point something to the
     effect that, although this series is good for estimating low resolution temperature
     variability, it may dampen high frequency variability.  if my memory is correct in this
     case, would you please send gabi the record you consider best for comparing with the
     model predicted interannual response to volcanic eruptions?
     on another matter we are extending our runs back in time - I have now compiled a record
     of global volcanism back to 4000 BP for both hemispheres - extended back to 8000 BP for
     30-90N.  we are therefore trying to compile paleo records older than AD 1000 to at least
     get some reconstruction we can compare with.
     I seem to recall that Keith or you may have published some longer reconstructionn but
     cannot recall where it is?  if so, would you be so kind as to send it to me?  also I am
     trying to find a long record from the eastern California for the bristlecone pine - for
     some reason I am having difficulty finding one.  if you have a long record - even going
     back beyond 2000 BP, it would be very much appreciated.
     thanks for any help you can give us on this and best wishes, Tom
     --
     Thomas J. Crowley
     Nicholas Professor of Earth Systems Science
     Dept. of Earth and Ocean Sciences
     Nicholas School of the Environment and Earth Sciences
     Box 90227
     103  Old Chem Building
     Duke University
     Durham, NC  27708
     tcrowley@duke.edu
     919-681-8228
     919-684-5833  fax

     Prof. Phil Jones
     Climatic Research Unit        Telephone +44 (0) 1603 592090
     School of Environmental Sciences    Fax +44 (0) 1603 507784
     University of East Anglia
     Norwich                          Email    p.jones@uea.ac.uk
     NR4 7TJ
     UK
     ----------------------------------------------------------------------------

   --
   Professor Keith Briffa,
   Climatic Research Unit
   University of East Anglia
   Norwich, NR4 7TJ, U.K.

   Phone: +44-1603-593909
   Fax: +44-1603-507784
   [1]http://www.cru.uea.ac.uk/cru/people/briffa[2]/

