cc: Mike Mann <mannatXYZxyzginia.edu>

date: Wed, 21 Feb 2001 08:54:41 +0800

from: Scott Rutherford <srutherfordatXYZxyzginia.edu>

subject: Re: verification results

to: Tim Osborn <t.osbornatXYZxyz.ac.uk>

Dear Tim,

First, I put together a new results page at

http://holocene.evsc.virginia.edu/~rutherfo/results. The page has a

plot of northern hemisphere mean temperature for each run and a link

to more detailed plots and the annual maps. Note that there is a link

at the top of the page for the first 1400-1856 reconstruction using

the mxd data and compared to the Mann et al. reconstruction. This is

for the annual mean and uses 366 mxd proxies. I don't use all 387

becuase there are some that don't reach 1856 and trying to fill these

missing values increases the run time by several orders of magnitude.

Other 1400-1856 reconstructions are running.

Regarding the MXD errors. It would be nice to have them, but I view

that as a minor point and your time is probably better spent

elsewhere seeing as they are not easy to get.

I will work on calculating the variance sums over only available

temperature values if you want to do the mxd gridpoint comparisons.

Also, if you have a minute I could use some IDL help. I have an IDL

data file that I don't know what to do with (since I don't know a

thing about IDL). Would you be willing to convert it to something I

can deal with (matlab, netCDF, ascii)? The data file is global

oceanic primary production.

Regards,

Scott

>Dear Scott and Mike,

>

>sorry for the lack of response to your e-mail in January. I've been away

>quite a bit and then had three proposal deadlines come up last week, so was

>rather busy. The results look *very* promising, with good verification

>statistics etc. The multivariate resolved variance is only slightly higher

>for the warm season than for the cold season which is a little surprising,

>though I guess warm & cold seasons are more strongly correlated for the

>leading covariance structures that are most highly weighted than for the

>smaller scale variations that are suppressed. A couple of specific things:

>

>(1) MXD errors. A really useful measure that one can use here is the EPS

>(Expressed Population Signal), based on the mean correlation between the

>tree cores that make up each chronology (rbar), and the number of tree

>cores (n). Time-dependence can be included by putting the time-varying

>number of tree cores into the EPS equation. This would give some measure

>of the 387 chronologies. For the gridded case, some improvement would have

>to be estimated for the many grid boxes that contain >1 chronology, but

>that's not difficult to do. What is *difficult* is that I don't have

>either rbar or n for each chronology! All I have is, for each year and

>each chronology, the number of tree cores with data expressed as a fraction

>of the maximum number of tree cores for that chronology, i.e.,

>fraction(x,t) = n(x,t) / nmax(x). Since I don't know nmax for each

>chronology x, I can't work out n(x,t) from fraction(x,t). Nor do I know

>rbar(x). I've been wanting to get rbar(x) and n(x,t) ever since I started

>using this tree-ring data set (1997), but it's apparently not easily

>available. How important do you think it is for the current piece of work?

> If it is important then I could try to get it again, but if it's a fairly

>minor side issue then I won't.

>

>(2) From what I remember about the plan of action, the idea was to do these

>first runs using the already infilled instrumental data (though of course

>witheld for the pre-1901 period). I assume, therefore, that the timeseries

>and statistics shown are from this infilled & complete data set (I see now

>from the annual maps that this *is* the case because the "raw data" maps

>are complete). It would be useful to compare these MXD-based

>reconstructions with the instrumental data by sampling only those grid

>boxes in both the raw and reconstructed fields that originally contained

>real data in the instrumental data set. [I assume that the infilled

>instrumental data will be the same as the original instrumental data for

>these grid boxes.] The comparisons/statistics shown are useful, but only

>in addition to the comparison done against the (subsampled) original data,

>because (i) the message is harder to get across when using already infilled

>data; and (ii) the statistics *might* be slightly (artificially) improved

>when using infilled data. If you'd prefer me to do this, then let me know

>where the data sets are (plus format) and I can compare against my copy of

>the Jones instrumental data.

>

>So I guess that you should have enough to talk about at the EGS in Nice

>then Mike? Please let me know if you need any further input from me at

>this stage.

>

>Best regards to you both,

>

>Tim

>

>

>

>

>

>Dr Timothy J Osborn | phone: +44 1603 592089

>Senior Research Associate | fax: +44 1603 507784

>Climatic Research Unit | e-mail: t.osbornatXYZxyz.ac.uk

>School of Environmental Sciences | web-site:

>University of East Anglia __________| http://www.cru.uea.ac.uk/~timo/

>Norwich NR4 7TJ | sunclock:

>UK | http://www.cru.uea.ac.uk/~timo/sunclock.htm

--

______________________________________________

Scott Rutherford

University of Virginia University of Rhode Island

Environmental Sciences Graduate School of Oceanography

Clark Hall South Ferry Road

Charlottesville, VA 22903 Narragansett, RI 02882

srutherfordatXYZxyzginia.edu srutherfordatXYZxyz.uri.edu

phone: (804) 924-4669 (401) 874-6599

fax: (804) 982-2137 (401) 874-6160

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