Monday, May 21, 2012

4538.txt

cc: "David Pugh" <d.pughatXYZxyz.com>, "Phil Jones" <p.jonesatXYZxyz.ac.uk>, "Kennedy, John" <john.kennedyatXYZxyzoffice.gov.uk>
date: Thu, 11 Jun 2009 10:49:57 +0100
from: "Parker, David" <david.parkeratXYZxyzoffice.gov.uk>
subject: RE: SST bias advice
to: "Philip Woodworth" <plwatXYZxyz.ac.uk>

Philip

For bucket corrections, see Fig. 18 of the attached paper (Folland and
Parker, 1995). In June 1860 near the Falklands (upper left panel), the
estimated correction is less than 0.1 deg C. An underlying assumption is
that about 75% of buckets were wooden at that time (Section 8d on page
351). However the instrumentation is likely to have varied from ship to
ship, and unless we know what was done on board the Erebus, we cannot be
absolutely sure of the bias.

The Folland and Parker (1995) corrections are relative to a modern
(1951-1980) mix of in situ SST data from engine intakes, insulated and
uninsulated buckets and hull sensors. Corrections relative to the
1961-1990 reference period we now use will be very similar, but Thompson
et al (2008)* have now pointed out the need for corrections to modern
data. As AVHRR data are calibrated using buoys, and buoys appear to be
biased slightly cold compared to ships (consult John Kennedy for more
details), then the AVHRR may be biased cold, by an amount approaching
0.1 deg C, fortuitously yielding next-to-no bias relative to wooden
buckets in Falklands winter!

* Thompson D.W.J., Kennedy, J.J., Wallace J.M., Jones, P.D. 2008: A
large discontinuity in the mid-twentieth century in observed global-mean
surface temperature. Nature, 453, 646-649 doi:10.1038/nature06982.

Regarding the contents of ICOADS, see http://icoads.noaa.gov/ and/or
contact Scott Woodruff.

I hope this helps,

Regards

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.parkeratXYZxyzoffice.gov.uk
Website: www.metoffice.gov.uk

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



-----Original Message-----
From: Phil Jones [mailto:p.jones@uea.ac.uk]
Sent: Thursday, June 11, 2009 9:34 AM
To: Parker, David
Cc: Philip Woodworth; David Pugh
Subject: Fwd: SST bias advice


Philip,
Been away Tues/Wed. Sending this reply back via David Parker, in
case he has some more thoughts.
First I'm not sure how much SST data are in ICOADS (even the
CLIWOC work as well) from obs taken while a ship is in port or at
anchor. I'd presume they get included, but they would seem like pier
obs, so may be flagged as such. When I say flagged, you'd only know by
looking at the locations and noticing these don't change for a month!
Presumably the SST obs were taken with a bucket, which in the 1840s
would have been a wooden bucket. This bias from wooden buckets is
smaller
than with the later canvas buckets (1890s to 1940s). David can
probably tell you what this would be for wooden buckets in the 1850s. My
guess is that it would be quite small - any adjustment for it would be
an increase of between 0 and 0.2deg C, probably near the lower end.

I also think you're better off talking to David than Dick Reynolds.

Cheers
Phil

>Date: Tue, 09 Jun 2009 08:48:04 +0100
>From: Philip Woodworth <plwatXYZxyz.ac.uk>
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>
>Hi Phil,
>
>Have you any advice on the below? I sent this to Reynolds in NOAA
>but I am not sure he is around still? Anyway, as you were a
>co-author of the IPCC chapter I wondered if you might have some
>idea. I think I mentioned previously our work in the Falklands:
>
>
>I would be very grateful for advice on likely bias in a set of
>historical sea surface temperature measurements compared to the
>primarily AVHRR ones of today. I have read up a bit on this subject
(the
>appendix to the measurement chapter in the 4AR was very useful) but
>still find it hard to grasp what the possible biases might be.
>
>We are making comparisons of sea level measured in the Falklands in
1842
>by James Clark Ross to those of today, and in part of that work we
>compared Ross's 'mean temperature of the sea surface' (see attached tif
>image of one page of his journal) with those from the 'sst.mnmean.nc'
>file from the CDC for 1981 onwards which is based on your (Reynolds)
>2002 work.
>
>The Ross temperature for southern winter 1842 is about the same as you
>get for a similar time of year in the CDC file (about 4.1 deg C). But
do
>you have any feel for how they might be relatively biased and, if so,
>have you a reference we could quote? I realise this is a bit of long
>shot - there is no information in his book I have found explaining how
>the temperature measurements were made or the time of day.
>
>Many thanks in advance for the advice.
>
>Phil Woodworth
>
>--
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>
>

Prof. Phil Jones
Climatic Research Unit Telephone +44 (0) 1603 592090
School of Environmental Sciences Fax +44 (0) 1603 507784
University of East Anglia
Norwich Email p.jonesatXYZxyz.ac.uk
NR4 7TJ
UK
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