date: Wed, 3 Jun 2009 15:07:25 +0100
from: "Parker, David" <david.parker@metoffice.gov.uk>
subject: RE: Tom's thoughts on urban errors ...
to: "Thorne, Peter (Climate Research)" <peter.thorne@metoffice.gov.uk>, "Phil Jones" <p.jones@uea.ac.uk>, "Stott, Peter" <peter.stott@metoffice.gov.uk>

Peter

Thanks. I agree we should ask Tom for the actual numeric metadata or its
on-line address.

David


David Parker, Climate Research scientist
Met Office Hadley Centre  FitzRoy Road  Exeter  Devon  EX1 3PB  United
Kingdom
Tel: +44 (0)1392 886649  Fax: +44 (0)1392 885681
Email: david.parker@metoffice.gov.uk  
Website: www.metoffice.gov.uk

See our guide to climate change at
http://www.metoffice.gov.uk/climatechange/guide/

-----Original Message-----
From: Thorne, Peter (Climate Research) 
Sent: Wednesday, June 03, 2009 2:34 PM
To: Phil Jones; Parker, David; Stott, Peter
Subject: Tom's thoughts on urban errors ...

Hi, Peter,
   The attached paper describes the rural/urban metadata we have for
most stations in GHCN (at least as of 1999). We should be able to easily
provide you with both the map and night lights metadata, as I believe
they are on-line with GHCN.
    My personal view is:  I heard the world's foremost urban meteorology
expert, Tim Oke (Canada), say that urbanization takes place on three
scales: micro (on the scale of a garden), local (on a scale of a park)
and meso (on the scale of the city).  Of the three, he said the mirco is
most important and the meso is least.  I have seen a lot of lousy urban
heat analysis, such as papers which looked at the temperature difference
between rural and urban but used the temperature difference itself as
the metric for which was the most urban and most rural.  Of the analyses
that seemed robust, they tend to find little or no uhi bias in
homogeneity adjusted data. My view is that this is because the
adjustments to account for sudden changes in the micro and local scales
which, by the very nature of comparison to neighboring stations, adjusts
for subtle meso scale biases.  Everybody wants to add an estimate of
what UHI bias might be into their error bars, but it seems to me that
rather than trust folk lore that there is a uhi bias, they first need to
find one systematically in the network. Until they do that, the former
is just hand waving to appease the know-littles.  Jim Hansen adjusts his
urban stations (based on night-lights) to nearby rural stations, but if
I recall correctly (I'll send that paper shortly), he warms the trend in
42 percent of the urban stations indicating that nearly half have an
urban cold bias.  Yet error analyzers want to add a one sided extra
error bar for uhi.....
          Regards,
                  Tom
-- 
Peter Thorne   Climate Research Scientist
Met Office Hadley Centre, FitzRoy Road, Exeter, EX1 3PB
tel. +44 1392 886552 fax +44 1392 885681
www.metoffice.gov.uk/hadobs
