cc: santer1@llnl.gov, wigley@ucar.edu, Mike Wallace <wallace@atmos.washington.edu>, Phil Jones <p.jones@uea.ac.uk>
date: Wed, 10 Dec 2008 11:11:46 -0700
from: Kevin Trenberth <trenbert@ucar.edu>
subject: Re: A new paper on 20th century global-mean temperature variability
to: David Thompson <davet@atmos.colostate.edu>

   David
   This looks like a very valuable contribution.  I have a few suggestions.
   Firstly you may find the following two publications of interest
   Trenberth, K. E., and D. J. Shea, 2005: Relationships between precipitation and surface
   temperature. Geophys. Res. Lett., 32, L14703, doi:10.1029/2005GL022760.[[1]Paper (.pdf)]
   Trenberth, K. E., and A. Dai, 2007: Effects of Mount Pinatubo volcanic eruption on the
   hydrological cycle as an analog of geoengineering. Geophys. Res. Lett., 34, L15702,
   doi:10.1029/2007GL030524. [2][PDF]
   The first paper notes that there are strong relationships between precipitation and surface
   temperature that vary with latitude and season.  Over land there is a strong negative
   correlation in summer extratropical continents and year round in tropics so that conditions
   are either hot and dry or cool and wet.  So this relates to wetter conditions also being
   cloudier and changing SH and LH surface fluxes, etc.  In winter at high lats the
   correlation is positive which is Clausius Clapeyron: warm and moist advection and ability
   of air to hold moisture.   Over oceans there are also some interesting relations, some
   governed by ENSO: high SSTs go with rain.
   Anyway you mention natural variability and the SLP field but some of this may be through
   the precip relation, not just flow of air from land to ocean to land etc.   You may want to
   at least mention this and the assoc mechanisms, and it may we a way to further reduce the
   "noise"?
   The second paper may be of interest wrt the volcanic eruption effects and the radiative
   forcing, and again the huge effect on rain and runoff.  Although not speculated on in the
   paper, we show that after Pinatubo there is a decrease in land precip.  We think this comes
   about in two stages.  1) the land cools more than ocean and the precip moves off shore, but
   at this stage there is no global decease in precip; then 2) there is a decease in
   evaporation and thus in global precip.
   For your study, this has two implications.  1) Part of the mechanism for influencing
   temperatures also comes through the precip link noted in paper (1) above.
   (2)  In your Fig 7 you have the effects stratified by total, land and ocean, and it would
   be of interest to also see  land minus ocean, and see whether the response is indeed
   quicker over land.   Eyeballing it, it seems so.
   Now a few other comments on the paper.  These are offered in the hope that it will help
   give the paper the impact it deserves.
   1) The figures could use some work.    Actually a lot of work.
   a) I urge you to add the zero line on all the time series.  This helps also to see whether
   the time series does have low frequency components.
   b) I urge you to add some labels on the y axis.  At least 0 and plus and minus 0.1C.
   (c) This sort of thing could easily be done in Illustrator.  If you don't use Illustrator
   for your figures, I strongly recommend it and can talk to you about it.  You can input ps
   files and generate eps, with nice labels and all sorts of touch ups, control of line widths
   and dot-dash types etc.   You can control the white space and layout nicely also.  In
   Illustrator you can also "save for microsoft" and it generates png files that are ideal in
   size for word documents or powerpoint, and so the size of the files is much reduced (e.g.
   from what you have).
   d) Fig. 2 is hard to see the white lines.
   (e) Fig 13 needs units on x axis:  months?
   2) The natural variability can, of course, also be affected by climate change and warming.
   A central question is how ENSO changes with climate change, for instance.  You method is
   good but you should acknowledge (more) that the "natural variability" may also contain some
   climate change signals.
   3) The difference in the effective heat capacity may also reflect the tropics (ENSO) vs
   global nature for volcanoes?   You may want to speculate about the implications of these
   figures for changes in solar forcing and especially the 111 year sun spot cycle.
   4) Alan Robock and Caspar Amann have a new volcanic forcing time series, pub in press in
   JGR I believe.
   Hope these help
   Kevin
   David Thompson wrote:

     Dear Kevin, Ben, Tom,

   Hope all is well.

   Mike Wallace, Phil Jones, John Kennedy (Met Office) and myself are about to submit a paper
   on the time-history of 20th century global-mean temperatures. The study is a follow-on to
   our study last summer which documented the discontinuity in SSTs in ~1945.

   Anyway, the paper is being passed around the authors for one last look, and we thought you
   might appreciate the chance to comment on the manuscript before it's submitted. I
   understand everyone is busy, especially at this time of year. And it's likely one or more
   of you will get the paper to review. But if you're interested and have any general
   comments, we'd appreciate your thoughts. Our rough plan is to submit within the first
   couple weeks after the New Year.

   The paper is attached as a doc file. And the figures are online at:

   [3]www.atmos.colostate.edu/~davet/outgoing/Figures_JClimate_Dec9.pdf

   Since it's at the (near-final) draft stage, please treat the work as confidential for now
   (ie please don't distribute the text or figures).

   Thanks,

   Dave

     =
         _______________________________________________________________________________

   --------------------------------------------------------------------
   --------------------------------------------------------------------
   David W. J. Thompson
   [4]www.atmos.colostate.edu/~davet
   Dept of Atmospheric Science
   Colorado State University
   Fort Collins, CO 80523
   USA
   Phone: 970-491-3338
   Fax: 970-491-8449

     =

--
****************
Kevin E. Trenberth                  e-mail: [5]trenbert@ucar.edu
Climate Analysis Section,           [6]www.cgd.ucar.edu/cas/trenbert.html
NCAR
P. O. Box 3000,                     (303) 497 1318
Boulder, CO 80307                   (303) 497 1333 (fax)

Street address: 1850 Table Mesa Drive, Boulder, CO  80305

