date: Tue Nov 10 09:18:48 2009 from: Phil Jones subject: Re: LvsO to: Tom Wigley Tom, The separate land and ocean datasets are merged around coasts and islands (at least for HadCRUT3). This means that you can't get back to the separate versions from the combined. If you look at the grids for a particular month you'll see many points the same in the separate land and ocean datasets, but weighted averages around the coasts and islands. We've been doing this since the early 1990s. We have altered how we do it. The next version will go back to a simpler weighting method than used in Borhan et al. (2006). Some grid boxes are in both. Differences will likely vary from year to year and within years due to sea ice. As for Anders Moberg's paper, I've no idea what NHT series he used. I'm presuming you mean his reconstruction as opposed to the instrumental series against which he calibrated the proxies. Splitting the variance into high and low probably has serious problems. All the high freq (<80 years) comes from trees with all the low freq coming from the other essentially uncalibrated proxies. Anders is OK, but I don't think he'd want to revisit this series. He tried to consider the implications of variance splitting in the attached paper. I recall it not being very convincing. Cheers Phil At 21:25 09/11/2009, Tom Wigley wrote: Hi Phil, Re land versus ocean, there is an interesting problem here, which may apply to all data sets. If I weight L and O "correctly" (not straightforward) then the weighted sum of L (CRUTEM3v) and O (HADSST2), as a global-mean time series will not be the same as the global mean direct from HadCRUT3v. This is because (I think) there are some gridpoints that appear in both the L and O data. Is this correct? I was rather surprised at how much my two versions of the L and O averages differed. However they were merged, I'm sure it could be done better, so as to minimize any inconsistencies like the one noted above. ----- On another point, what do you think of the Moberg (2005) series for NHT? I know you have worked with him, so he can't be all bad -- but this series is not only rubbish in terms of its variability, but it has been used by some arch skeptics to support their own silly ideas. Perhaps there is a chance that Moberg could re-do his series better? Tom. 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 ----------------------------------------------------------------------------