cc: "Wallace, John" <wallace@atmos.washington.edu>, "Jones, Phil" <p.jones@uea.ac.uk>, "Kennedy, John" <john.kennedy@metoffice.gov.uk>
date: Fri, 09 Nov 2007 11:38:42 +0000
from: David Parker <david.parker@metoffice.gov.uk>
subject: Re: A discontinuity in surface temperature observations
to: David Thompson <davet@atmos.colostate.edu>

Dave, Mike

Thanks. I somewhat misinterpreted your original email as referring to a
one-month "blip" in August 1945, as I didn't receive the diagrams. Now
it is clear that you meant a sudden "cooling" to a sustained (for
several years) lower temperature.

It might be worth including John Kennedy as a co-author of your paper on
20th century climate variability. He has made an attempt to correct
uncorrected biases in HadSST2 during the 2nd World War by splitting the
data into individual countries and then calculating climatologies for
1940-1970 for each country, thus removing any relative biases (which are
strongly related to recruiting country of the ship) over the climatology
period. He then recombined the different countries into a single
'corrected' HadSST2. The effect was to reduce the height of the 2nd
World War peak and also to reduce the depth of the subsequent fall in
1945. Like Phil, however, we note that during this period, there are
fewer observations so the uncertainties are likely to be larger.

John notes that the problems are particularly marked in the southern
hemisphere:

http://hadobs.metoffice.com/hadsst2/diagnostics/hemispheric/southern/


It looks like the rapid changes are due to rapid changes in the mix of
countries available in ICOADS. We have had over a million new data for
the 2nd World War period digitised in the project Phil mentioned, and
these data do not show such a big peak in the early 1940s or such a big
fall in 1945. However these newly-digitised data are not yet
incorporated in HadSST2 and their inclusion in our analyses is only
likely to be done in the next financial year (April 2008-March 2009).
Marine air temperatures also have problems in the 2nd World War so may
not help; we are giving priority to sea surface temperature.

So whatever John may be able to contribute to your paper won't be the
final word!

Regards

David



On Fri, 2007-11-09 at 08:27 +1100, David Thompson wrote:
> Phil, David,
> 
> 
> Thanks so much for the quick responses. Some quick comments:
> 
> 
> 1. the temperature drop in 1945 is evident in NMAT data, earlier
> HadSST products and the MoHSST products.
> 2. the drop is also apparent if you freeze the domain to only those
> grid boxes available 41-44.
> 3. if you look at, for example, the FAR Summary for Policymakers, you
> can really see the 0.3 K drop reflected in the key global mean time
> series.
> 
> 
> I'll do some more investigating and will send another email next week
> summarizing things in more detail.
> 
> 
> Thanks again for quick thoughts... 
> 
> 
> -Dave
> 


-- 
David Parker   Met Office Hadley Centre   FitzRoy Road EXETER EX1 3PB UK
E-mail: david.parker@metoffice.gov.uk
Tel: +44-1392-886649  Fax: +44-1392-885681  http:www.metoffice.gov.uk
