Thursday, May 24, 2012

4667.txt

date: Wed Mar 21 10:15:04 2001
from: Tim Osborn <t.osbornatXYZxyz.ac.uk>
subject: Re: question
to: Scott Rutherford <srutherfordatXYZxyz.uri.edu>

At 12:23 19/03/01 +0800, you wrote:

>In the reconstruction you show in your comparisons there is cool
>interval around 1450 that is not really picked up by the RegEM
>method. In the NH reconstruction that you sent me last week, that
>cool period doesn't show up nearly as much. Is that a difference
>between age banded and conventional?

It's not so much a difference between the tree-ring standardisation (i.e., age-banded versus conventional), but more related to the slight difference in the way the tree-rings are combined together to produce a hemispheric time series. When there are lots of data (i.e. after about 1650) then it doesn't make much difference how they are combined, but before this the results are quite sensitive (i.e., a straight average, or average into regions then into hemispheric mean, or average all trees, or exclude the very young or very old trees - these things all make quite a difference!). See figure 4 of Briffa et al. (2001) for an example of this sensitivity. I've put a pdf of this paper on our anonymous ftp site (ftp.cru.uea.ac.uk/people/timosborn/Briffa2001.pdf) in case you don't have a copy - though the colour figures are pretty poor quality in this pdf file.

Briffa KR, Osborn TJ, Schweingruber FH, Harris IC, Jones PD, Shiyatov SG and Vaganov EA (2001) Low-frequency temperature variations from a northern tree-ring-density network. Journal of Geophysical Research 106, 2929-2941.

>Also, can you send me your mask that you are applying. I only have
>your landmask.

The mask is attached. Self explanatory, including coordinates of the grid (these are the lat,lon of the centre of each box). This contains all the boxes with tree-density chronologies in that we used. Coverage decreases back in time of course - did you want the time-dependent mask (much bigger file, with one field per year from 1400-1900)?

>I just wanted to check in and see how things were going.

Pretty busy here - I'm trying to get the age-banded comparisons done, but I'm also busy finishing some work for my visit to NCAR - I leave on the 31st March and still have work & talks to do!

>1) Do you need anything else from me?

No.

Cheers

Tim


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