date: Tue Mar 18 08:56:28 2008
from: Phil Jones <p.jones@uea.ac.uk>
subject: Re: Urgent
to: "Rachel Warren" <r.warren@uea.ac.uk>

    Rachel,
       Here's a few sentences.  You can pick and choose which bits you want.
    Description of HadCRUT3(v) - the dataset names. CRU does the land and the Hadley Centre
    the ocean.

   Over land regions of the world over 3000 monthly station temperature time series are used.
   The basic monthly average temperature series are collected by the National Meteorological
   Services around the world. Coverage is denser over the more populated parts of the world,
   particularly, the United States, southern Canada, Europe and Japan. Coverage is sparsest
   over the interior of the South American and African continents and over the Antarctic. The
   number of available stations was small during the 1850s, but increases to over 3000
   stations during the period since 1951. For marine regions sea surface temperature (SST)
   measurements taken on board merchant and some naval vessels are used, supplemented by buoy
   data in recent decades. As the majority come from the voluntary observing fleet, coverage
   is reduced away from the main shipping lanes and is minimal over the Southern Oceans.
   CRU has spent many person years assessing the long-term homogeneity of the land station
   record and the Hadley Centre a similar time undertaking complementary assessments of the
   homogeneity of the marine data.
   Stations on land are at different elevations, and different countries estimate average
   monthly temperatures using different methods and formulae. To avoid biases that could
   result from these problems, monthly average temperatures are reduced to anomalies from the
   period with best coverage (1961-90). For stations to be used, an estimate of the base
   period average must be calculated. Because many stations do not have complete records for
   the 1961-90 period several methods have been developed to estimate 1961-90 averages from
   neighbouring records or using other sources of data. Over the oceans, where observations
   are generally made from mobile platforms, it is impossible to assemble long series of
   actual temperatures for fixed points. However it is possible to interpolate historical data
   to create spatially complete reference climatologies (averages for 1961-90) so that
   individual observations can be compared with a local normal for the given day of the year.
   Both the component parts (land and marine) are separately interpolated (as anomalies from
   1961-90) to the same 5 x 5 latitude/longitude grid boxes. The combined versions (HadCRUT3
   and HadCRUT3v) take values from each component and weight the grid boxes according to their
   errors in estimation, so giving greater weight to the oceanic data as errors of estimate
   are generally smaller.
   The gridded surface temperature products (HadCRUT3 and HadCRUT3v) extend from 1850 up to
   present.
   Both HadCRUT3/HadCRUT3v and the separate land and marine grids (CRUTEM3 and HadSST2) are
   used extensively within WG1 of AR4, principally within Chapter 3 on 'Observations:
   Atmospheric Surface nd Climate Change', but the datasets in their various forms are used in
   Chapter 1 (Historic overview of Climate Change Science), Chapter 6 (Paleoclimate), Chapter
   8 (Climate Model Evaluation) and Chapter 9 (Understanding and Attributing Climate Change),
   as well as in WG2.
    Cheers
    Phil
   At 19:33 17/03/2008, Rachel Warren wrote:

     Hi Phil
     I went to see Simon Clegg - and ufnortunately need to trouble you
     again - sorry.
     Simon Clegg has emphasised that there really needs to be a section on
     the CRU temp record
     in the IPCC ENV research section in the ENV report.  This means a
     paragraph on how the CRU temp record
     is put together and where it is used in IPCC.  Simon insists that what
     is in the 2006/5 ENV report
     doesn't explain HOW the temp record is put together which is what he
     wants ....ie where data
     is collected from, how collated, what did CRU actually do, for how long etc ....
     Can you help?   I'm going to be VERY unpopular if I don't hand this in
     complete on Wednesday so
     please can you send me something tomorrow?
     Thanks
     Rachel
     --
     Dr Rachel Warren
     Senior Research Fellow
     Tyndall Centre
     Zuckermann Institute
     University of East Anglia
     Norwich NR4 7TJ
     Telephone 01603 593912
     Fax 01603 593901
     E-mail r.warren@uea.ac.uk

   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.jones@uea.ac.uk
   NR4 7TJ
   UK
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