date: Tue Mar 18 08:56:28 2008 from: Phil Jones subject: Re: Urgent to: "Rachel Warren" 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 5º x 5º 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 ----------------------------------------------------------------------------