From: P.Jones@uea.ac.uk
To: david.parker@metoffice.gov.uk
Subject: RE: UHI corrections
Date: Wed, 18 Jul 2007 13:21:59 +0100 (BST)
Cc: "Jenkins, Geoff" <geoff.jenkins@metoffice.gov.uk>, "Jones, Phil" <p.jones@uea.ac.uk>

 Geoff,
  David is essentially right. In 1986 we rejected
 38 (if my memory from 1986) is correct!  I don't
 recall the number we looked at so I can't give a
 percentage, as I'm not that much of a trainspotter.
  The % would be small though, as we looked the
 homogeneity of about 2500 then. Also some which
 might have been affected by urbanization might have
 been rejected for other reason. I'm half asleep here
 in my hotel room in Beijing (same hotel as the IPCC
 meeting David!) as it is just gone 8pm! I have the
 pdf of the 1986 paper and 38 rejected for urban
 warming trends (31 in N. America and 7 in Europe
 - none elsewhere) out of 2666. 239 were rejected for
 other reasons.

   Brohan et al is the best reference. We included
 urbanization as one of the biases (one sided as urban
 should lead to warming, so if you look very, very
 closely at the error range in the paper you'll
 see it is slightly one-sided.

   I've been giving some talks here and have more tomorrow.
 At CMA I've found they have a homogenized dataset of 745
 stations for the country which they are preapred to give
 me at some point for inclusion. They have adjusted for all
 site moves but not for urbanization. It seems that it
 is almost impossible for sites here to be rural (maybe only
 1% of the total). Sites move out of the city at regular
 intervals as the cities expand. So Beijing has 6-7 site
 moves since 1951!  Also China seems to be the only
 country that doesn't use airport sites. None are located
 at airports.  I'm going to give them my Chinese sites
 in return so they can do some comparisons. I'll
 talk with their person (Mr Li ) more tomorrow.

  Another interesting bit of work here is that they also
 have an homogenized set of monthly wind speed data from 1951.
 Not sure how they homogenize this for site moves, but
 almost all the sites (about 200) show declines in mean
 wind speeds since 1951. NCEP and ERA-40 also show this
 for wind speeds at 1000, 925 and 850hPa as well. Odd thing
 is that they think the decline in wind speeds is due
 to urbanization! - Li's English isn't great though, so
 I could be wrong. Another person I've been talking to
 has been looking at precip trends from 1951 - again
 they think declines in N. China are due to urbanization!
 Odd then that there are increases in S. China, which is
 also urbanized at similar rates.

   Air quality here is awful - I saw the sun for the first
 time since arrival on Sunday, after a long downpour cleared
 the air this morning! The haze will be back tomorrow. Apparently they
 will closing the worst factories and getting half the cars
 off the road next August for the Olympics! Traffic might
 flow better for the latter, but can't see the former
 doing that much good. What they need to do is to get
 a heavy downpour every early morning!

 Cheers
 Phil


> Geoff
>
> It is correct that Phil Jones removes stations that appear to have urban
> warming, unlike Hansen et al. who correct them. I don't know the
> percentage of stations that Phil removes; details were probably
> originally given in the Jones et al 1985 and 1986 USDoE reports (see
> references given in Jones and Moberg, 2003 (attached); the reports are
> probably only available on paper and are not now in my collection of
> box-files!) and could take some time to collate. But to do this might
> not be useful as Phil could have rejected further stations from the
> additional datasets he accrued since then. Nevertheless I expect the
> rejection rate is small.
>
> Brohan et al is the best reference for a discussion of the urbanization
> uncertainty in land surface air temperatures.
>
> I hope this helps somewhat.
>
> Regards
>
> David
>
>
> On Wed, 2007-07-18 at 11:46 +0100, Jenkins, Geoff wrote:
>> David
>>
>> If I understand Phil right, there are no stations which are CORRECTED
>> for UHI effects, but there are several (roughly what percentage?) which
>> are REMOVED. I would be grateful if you could give me the best ref to
>> this (is it Brohan et al 2006), to pass to an outside sceptical enquirer
>> (one Nigel Lawson, remember him?). He already knows about yr recent
>> windy/calm comparison paper via the "Briefing" booklet I did.
>>
>> Thanks
>>
>> Geoff
>>
>> -----Original Message-----
>> From: P.Jones@uea.ac.uk [mailto:P.Jones@uea.ac.uk]
>> Sent: 16 July 2007 21:59
>> To: Jenkins, Geoff
>> Subject: Re: UHI corrections
>>
>>
>>
>>  Geoff,
>>    In China this week and away next week. Best Ref is
>>  really Ch3  of AR4 (IPCC). We don't make adjustments
>>  just remove the stations affected.
>>
>>    Best if you contact David Parker. There is also
>>  some stuff in Brohan et al. (2006) in JGR. Also
>>  David P has a couple of papers on the subject.
>>
>>   We incorporate possible residual urban effects into
>>  the error estimates of global T.
>>
>>  Cheers
>>  Phil
>>
>>
>> > Phil
>> >
>> > Sorry to keep bombarding you. What is the best ref to your corrections
>>
>> > of land surface temps (in CRUTEM, presumably) for heat island effects,
>>
>> > please?
>> >
>> > Geoff
>> >
>> > Dr Geoff Jenkins
>> > Manager, Climate Change Scenarios
>> > Hadley Centre
>> > Met Office
>> > FitzRoy Road, EXETER, EX1 3PB, UK
>> > tel: +44 (0) 787 966 1136
>> > geoff.jenkins@metoffice.gov.uk
>> > www.metoffice.gov.uk
>> >
>> >
>>
> --
> 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
>
>
>



