To: t.m.melvin@uea.ac.uk

Subject: Fwd: Re: Standardisation uncertainty for tree-ring series

Date: Fri Apr 28 15:34:54 2006

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Date: Fri, 28 Apr 2006 15:08:05 +0100

To: philip.brohan@metoffice.gov.uk

From: Tim Osborn <t.osborn@uea.ac.uk>

Subject: Re: Standardisation uncertainty for tree-ring series

Cc: Keith Briffa <k.briffa@uea.ac.uk>,simon.tett@metoffice.gov.uk

Hi Philip,

we have three "groups" of trees:

"SCAND" (which includes the Tornetrask and Finland multi-millennial chronologies, but

also some shorter chronologies from the same region). These trees fall mainly within

the 3 boxes centred at:

17.5E, 67.5N

22.5E, 67.5N

27.5E, 67.5N

"URALS" (which includes the Yamal and Polar Urals long chronologies, plus other shorter

ones). These fall mainly within these 3 boxes:

52.5E, 67.5N

62.5E, 62.5N (note this is the only one not at 67.5N)

67.5E, 67.5N

"TAIMYR" (which includes the Taimyr long chronology, plus other shorter ones). These

fall mainly within these 4 boxes:

87.5E, 67.5N

102.5E, 67.5N

112.5E, 67.5N

122.5E, 67.5N

We do some analysis at the group scale, and for this we take the JJA temperatures from

each box and average to the group scale to obtain a single series from each of SCAND,

URALS and TAIMY.

We do some analysis at the overall scale, and for this we take these three group

temperature series and average them to get an overall NW Eurasia temperature for boxes

with tree chronologies in them.

We did also try using a wider average for the region, including all LAND temperatures

from grid boxes within a rectangular region from 12.5E to 127.5E and from 57.5N to

72.5N, but I don't think it correlated so well against the tree-ring width data (I can't

remember the exact correlations), so we didn't pursue that.

Does that give you enough information to be going on with? I'd recommend using CRUTEM3

rather than HadCRUT3, because the correlations seem to deteriorate with the inclusion of

SST data in some cases -- though of course you can look into this yourself.

Cheers

Tim

At 16:35 27/04/2006, philip.brohan@metoffice.gov.uk wrote:

Thanks Tim.

I need to extract from the instrumental and model data the appropriate

data to calibrate the tree-rings against. Presumably this is the

June-July-August average land surface temperature for a particular

region in NW Eurasia. Could you send me the lat and long ranges of the

region?

Cheers,

Philip

On Thu, 2006-04-27 at 16:01, Tim Osborn wrote:

> Thanks for the nice precise description of methodology, Philip. It's

> good that we are all clear exactly what procedure is to be applied.

>

> On the train after our meeting last week, Keith and I discussed this

> a bit more. In the NW Eurasian case study, n is quite high and

> therefore it is likely that the bootstrap estimates will show

> relatively little variation and probably will underestimate the true

> error (due to additional errors in the assumptions underlying RCS, as

> discussed in London). We will do the calculations anyway, and then

> we will know for sure how large/small they are, rather than just speculating.

>

> It looks likely that Tom Melvin will have time to devote directly to

> this issue as he will probably be funded by our (that includes you,

> Simon) NERC RAPID project for a while. Once/if this is confirmed,

> then we'll get Tom to do the calculations outlined below and

> communicate directly with Philip over any implementation issues etc.

>

> Cheers

>

> Tim

>

> At 16:02 26/04/2006, philip.brohan@metoffice.gov.uk wrote:

> >Keith, Tim.

> >

> > At our meeting last Wednesday I agreed to specify exactly what needed

> >to be done to make uncertainty estimates for standardisation of the

> >tree-ring data.

> >

> > Suppose we are making a proxy series from n cores. From those n cores

> >we can make an RCS age correction curve, and a mean proxy series (the

> >average of the cores after applying the age correction curve to each

> >one?). These are the best-estimate values for the age-correction curve

> >and the proxy series.

> >

> > We also need bootstrap estimates of the age correction curve and the

> >mean proxy series. To make a bootstrap estimate: sample, with

> >replacement, from the n cores until you have a set of n samples. (Some

> >of the cores will be in this sample once, some several times, and some

> >not at all). From this set of n samples, make an age correction curve

> >and a mean proxy series as before. These are the bootstrap estimates.

> >

> > We need a lot of bootstrap estimates. I'd like 1000 - 100 will probably

> >do at a pinch. So please can you make these and send me the 1001 age

> >correction curves and 1001 mean proxy series.

> >

> > I will do something similar with the instrumental series, and we can

> >then make bootstrap estimates of the regression uncertainty and the

> >uncertainty in the reconstructed temperatures.

> >

> >Cheers,

> >

> > Philip

> >

> >--

> >Philip Brohan, Climate Scientist

> >Met Office Hadley Centre for Climate Prediction and Research

> >Tel: +44 (0)1392 884574 Fax: +44 (0)1392 885681

> >Global climate data sets are available from [1]http://www.hadobs.org

>

> Dr Timothy J Osborn

> Climatic Research Unit

> School of Environmental Sciences, University of East Anglia

> Norwich NR4 7TJ, UK

>

> e-mail: t.osborn@uea.ac.uk

> phone: +44 1603 592089

> fax: +44 1603 507784

> web: [2]http://www.cru.uea.ac.uk/~timo/

> sunclock: [3]http://www.cru.uea.ac.uk/~timo/sunclock.htm

--

Philip Brohan, Climate Scientist

Met Office Hadley Centre for Climate Prediction and Research

Tel: +44 (0)1392 884574 Fax: +44 (0)1392 885681

Global climate data sets are available from [4]http://www.hadobs.org

Dr Timothy J Osborn

Climatic Research Unit

School of Environmental Sciences, University of East Anglia

Norwich NR4 7TJ, UK

e-mail: t.osborn@uea.ac.uk

phone: +44 1603 592089

fax: +44 1603 507784

web: [5]http://www.cru.uea.ac.uk/~timo/

sunclock: [6]http://www.cru.uea.ac.uk/~timo/sunclock.htm

--

Professor Keith Briffa,

Climatic Research Unit

University of East Anglia

Norwich, NR4 7TJ, U.K.

Phone: +44-1603-593909

Fax: +44-1603-507784

[7]http://www.cru.uea.ac.uk/cru/people/briffa/

References

1. http://www.hadobs.org/

2. http://www.cru.uea.ac.uk/~timo/

3. http://www.cru.uea.ac.uk/~timo/sunclock.htm

4. http://www.hadobs.org/

5. http://www.cru.uea.ac.uk/~timo/

6. http://www.cru.uea.ac.uk/~timo/sunclock.htm

7. http://www.cru.uea.ac.uk/cru/people/briffa/

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