Thursday, December 29, 2011

1399.txt

cc: Tom Crowley <tcrowleyatXYZxyze.edu>
date: Fri, 01 Nov 2002 12:36:50 +0000
from: Phil Jones <p.jonesatXYZxyz.ac.uk>
subject: Re: paleo data
to: Gabi Hegerl <hegerlatXYZxyze.edu>,Keith Briffa <k.briffaatXYZxyz.ac.uk>

Gabi,
I have printed the files, but I do not know the answer. Keith is off today with a bad
back -
seeing a chiropractor. I need to talk to him before we can reply. I will be away Mon/Tues
next week, so we will not be able to reply until later next week.
Cheers
Phil
At 11:27 31/10/02 -0500, Gabi Hegerl wrote:

Dear Keith and Phil,
I checked and found that we did indeed use the JGR 2001 data (by reloading them
from your JGR data file). I also got the
1998 data from the volcano paper, and did some checking. My detection results
appear quite unimpressed by if I filter the 2001 data to focus on lower
frequencies or not (the estimated amplitudes of solar, volcanic and ghg signals
are virtually identical, volcanism gets a bit tougher to detect if you remove
the high-frequency component).
Then I redid the Epoch analysis comparing the
response of your data old and new to volcanism, and find somewhat bigger volcanic
signals on average (using 50 eruptions between 1400 and 1940) in the
JGR paper record. I high-passed both datasets and get somewhat more variability
in the JGR record, not the 1998 record.
I am wondering is there something I am overlooking?
I append a figure of the high-passed (var > ca 10 yrs removed) records,
and the volcanic response in both datasets (averaging years 1-20 after the eruption,
and removing the best-estimate solar and ghg signal before the analysis).
The analysis omits years with another volcanic eruption within the 20 yrs.
I also append one version of the figure where the upper 95%ile of the ghg signal (which
appears underestimated in Briffa 98 data) is removed rather than the
best estimate, in that case, the volcanic signals in both data appear nearly
identical.
Greetings, and please let me know if I am doing something wrong with your data!
Also, what is the best reference to a discussion on the difference between both
datasets?
Thanks in advance
Gabi

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). Te 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
[1]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 ) . I will soon be able to provide a 4000-year version , that is
now being worked on.
or a similar Northern tree-ring chronology incorporating more data eg see
[2]http://www.cru.uea.ac.uk/cru/people/briffa/qsr1999/
We do not have the bristlecone data - but they are available I presume from the
International Tree-Ring Data bank , part of the NGDC holdings?
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
tcrowleyatXYZxyze.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.jonesatXYZxyz.ac.uk
NR4 7TJ
UK
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--
Professor Keith Briffa,
Climatic Research Unit
University of East Anglia
Norwich, NR4 7TJ, U.K.

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

--

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gabriele Hegerl - NOTE CHANGE IN ADDRESS FORMAT
Department of Earth and Ocean Sciences,
Nicholas School for the Environment,
Box 90227
Duke University, Durham NC 27708
Ph: 919 684 6167, fax 684 5833
email: hegerlatXYZxyze.edu, [4]http://www.env.duke.edu/faculty/bios/hegerl.html

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.jonesatXYZxyz.ac.uk
NR4 7TJ
UK
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