date: Fri Jun  4 16:18:46 2004
from: Phil Jones <p.jones@uea.ac.uk>
subject: Re: hi, a quick question
to: Gabi Hegerl <hegerl@duke.edu>

    Gabi,
       The numbers Myles has may come from the paper Folland et al (2001) in GRL. In
    this paper OA was used to get error bars and these were smaller than the ones I
    got, by a factor of 1.5 to 2. I still think my numbers are nearer my gut feeling. They
    may be slightly smaller , but not half. This 2001 paper also incorporated error
    estimates on the basic obs, but I still have difficulty with some of these and how
    they relate to different timescales. Some errors are random, but some are biases
    so more systematic.
        Happy to read something when you have it in a state to send.  I think the GKSS
    runs have used a too large a value for the range of change in solar output. Also the
    volcanic forcing seems to get too much cooling. I suspect this occurs in winter as
    well as summer and it should only be in summer.
    Cheers
    Phil
   At 14:24 03/06/2004 -0400, you wrote:

     Thanks Phil!
     I don't know where Myles got his numbers, but your 97 paper says for decadal error std
     dev
     annual  0.068 for nh mean, and 0.05 to 0.06 for spring, summer autumn averages (first
     half
     of century). This is still an ok ballpark number, right?
     Does the 0.033 number ring a bell with you? I am going to go with your paper,
     unless I hear differently!
     (for what I am doing, small changes
     around the error estimate are not too bad, since we are just checking consistency of the
     residual
     between paleo and instrumental with our error assumption, which is quite an uncertain
     test)
     Thanks so much for your help, see you in Trieste!
     I think there are some cases now that paleo reconstruction variance cannot
     be straightforwardly compared with instrumental since its something a bit different.
     Hans has done some work on that with his runs, too.
     I'll keep in touch - and am keen on your opinion if you disagree with some of the
     things said!
     Gabi
     Phil Jones wrote:

      Gabi,
        I too am not sure what I've let myself in for !  I will find out soon in Trieste.
      I think you should try and compute what you want from the 1998 paper with the
      three of us (you, me and Tim Barnett). You can then use the options about
      autocorrelation used there.
        All the above is from the instrumental record. Paleo data will lose some variance,
     but
      this is difficult to estimate as it will depend on timescale. For decades I would
     expect
      it would need enhancing by a factor in the 1.2 to 1.5 range. So 1.3 is about the number
      I'd expect.
        My paper in J. Climate in 1997 may be useful to look at as well.
      Hope this helps. May have misunderstood some things.
      Cheers
      Phil
     At 11:30 02/06/2004 -0400, you wrote:

     Dear Phil,
     Congratulations (or commiserations) on the observations CLA!
     (got me for detn, and francis...hope this doesn't mean I can kiss science
     myself goodbye for a while...).
     I am checking some amplitude problems between paleo data and instrumental
     with Myles, and we are trying a tls approach since I need a good amplitude for
     my sensitivity. Myles' program can choose the noise level, so what we'd need
     is an estimate of the 1 std deviation uncertainty in
     decadal mean instrumental data 1880-1980, 30-90N annual (if 20-90N land growing
     is available, too, that would be great... and 5-yr averages), but any number
     would help.
     Or should I try compute it from the error estiamte in the 98 paper?
     What we found so far suggests that we should enhance the variance in paleo
     reconstructions a bit (not hugely, eg for Tom's reconstructions factor 1.3, will be
     more for less correlated data like Esper)
     So far, we assumed that the 1 std dev uncertainty is 0.033.... but that may be global?
     Greetings
     Gabi

     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
     ----------------------------------------------------------------------------

   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
   ----------------------------------------------------------------------------
