Saturday, April 28, 2012

3630.txt

date: Mon Sep 10 10:20:46 2007
from: Tim Osborn <t.osbornatXYZxyz.ac.uk>
subject: Re: Forcings
to: t.kleinenatXYZxyz.ac.uk

Thomas -- the HadCM3 volcanic forcing from Tett should *not* be the same as Crowley (2000)
forcing. Tett used Crowley (2003) and also implemented it as aerosol optical depth,
leaving the model to convert this to forcing. The Crowley (2003) and (2000) volcanic
spikes are indeed different magnitudes, however some of the bigger spikes are replaced by
smaller but longer-lasting spikes -- so the total integrated forcing (or smoothed forcing)
may be quite similar even though the spikes look quite different magnitude. The solar
forcing might be scaled differently -- certainly it was scaled differently for the ECHO-G
run compared with both Crowley (2000) and HadCM3/Tett.
Cheers
Tim
At 01:31 08/09/2007, you wrote:

Hi Tim.
Thanks for that data. I can recreate your figure from that, and I can also
produce something very similar from Crowley's original forcing data (see the
attached Total_forcing_be.jpg).
Using Simon Tett's forcing that is somewhat different, though. Crowley's solar
forcing seems to have been multiplied by some factor - 1.5 or so, I think,
but I'd have to check that figure, and the volcanoes seem to be stronger as
well - see the attached Tett_sol_volc.jpg, where we get a stronger pek for
the late 17th century, as well ast for the early 19th.
I guess I'll have to check the original source code, but climatic response
seems to indicate that the model really sees this (stronger) forcing.
Cheers,
Thomas

On Friday 07 September 2007, you wrote:
> Hi Thomas,
>
> after spending 20 minutes searching for the file, I've decided that I
> must have created my forcing graphic interactively rather than
> recording the steps in a program, so there's nothing to
> find. However, the file I used is 99% certain the attached file that
> I made by combining the ECHO-G solar and volcanic forcings
> (originally provided by Crowley 2000) with the appropriate conversion
> of solar (divide by 4, multiply by 1-albedo) and then added to that
> is my calculation of the forcing from CO2, CH4 and N2O (I took the
> concentrations of these gases used in the ECHO-G runs and converted
> them to radiative forcing using the IPCC TAR simple conversion formulae).
>
> NOTE-- please ignore the years column in the attached file, which are
> completely (and deliberately) wrong... the data runs from 901 to 1990.
>
> For presentation purposes (e.g. in a paper) I wouldn't use these
> anyway, due to omission of tropospheric sulphate aerosol forcing.
>
> Cheers
>
> Tim
>
> At 09:30 06/09/2007, you wrote:
> >Ooops, I overlooked that one.
> >This is what it looks like with the additional 0.3 factor...
> >
> >Cheers,
> >Thomas
> >
> >On Wednesday 05 September 2007, you wrote:
> > > gotta go now, I'll get my program and data file out tomorrow to give
> > > to you, but one thing is that to convert the solar "constant"
> > > variation to "forcing", you would not only divide by 4 but also
> > > multiply by 0.3 (i.e. one minus the planetary albedo)... obviously
> > > the albedo bit is done by HadCM3, but for simple models that don't
> > > bother to represent components that don't vary much, or for comparing
> > > with forcings that aren't affected by albedo, it's usually done by
> > > adjusting solar variations for the albedo.
> > >
> > > Cheers
> > >
> > > Tim
> > >
> > > At 16:15 05/09/2007, you wrote:
> > > >Hi Tim.
> > > >
> > > >I played around with those forcing timeseries some more...
> > > >
> > > >It's becoming even more intrigueing - now I have produced another
> > > > figure that is once again different from all the others.
> > > >
> > > >This one is from the timeseries we put into HadCM3, solar and volcanic
> > > >forcing.
> > > >Since solar forcing is a solar constant variation, I divided that by
> > > > four to get a radiative forcing. Then I determined the global annual
> > > > mean from the volcanic forcing timeseries, and added that to the
> > > > solar forcing timeseries.
> > > >
> > > >The figure is relative to the 1961-1990 mean, the thick black line is
> > > > 30yr gaussian filter.
> > > >
> > > >As far as I can understand it, this is pretty much what the model
> > > >sees, and it
> > > >is once again rather different from our other figures...
> > > >
> > > >Cheers,
> > > >Thomas
> > >
> > > Dr Timothy J Osborn, Academic Fellow
> > > Climatic Research Unit
> > > School of Environmental Sciences
> > > University of East Anglia
> > > Norwich NR4 7TJ, UK
> > >
> > > e-mail: t.osbornatXYZxyz.ac.uk
> > > phone: +44 1603 592089
> > > fax: +44 1603 507784
> > > web: [1]http://www.cru.uea.ac.uk/~timo/
> > > sunclock: [2]http://www.cru.uea.ac.uk/~timo/sunclock.htm

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