From	Phil Jones	Date	Fri, 01 Nov 2002 15:28:05 +0000
To	Keith Briffa
Subject	Fwd: Re: paleo data
X-Sender: hegerl@mail-he.acpub.duke.edu Date: Fri, 1 Nov 2002 09:56:45 -0500 To: Phil Jones From: Gabi Hegerl Subject: Re: paleo data No worries, I can wait till next week! It would be great to hear from you next week particularly if you feel I have overlooked something, I am planning to submit a little GRL paper on the detection results based on paleodata soon, and so a warning if I am doing something wrong would be great. Its not surprising that the detection results are stable, since other than volcanic forcing is mainly driven by the low-f component anyway. But it looks to me like the volcanic response is not smaller or even a bit larger in the annual JGR data (except for one real real big peak in the 1998 data). Greetings, have a good weekend and good luck for Keith's back Gabi 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 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 [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: hegerl@duke.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.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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: hegerl@duke.edu, [5]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.jones@uea.ac.uk NR4 7TJ UK ---------------------------------------------------------------------------- References 1. http://www.cru.uea.ac.uk/cru/people/briffa/jgr2001/Briffa2001.pdf 2. http://www.cru.uea.ac.uk/cru/people/briffa/qsr1999/ 3. http://www.cru.uea.ac.uk/cru/people/briffa/ 4. http://www.env.duke.edu/faculty/bios/hegerl.html 5. http://www.env.duke.edu/faculty/bios/hegerl.html