cc: k.briffa@uea.ac.uk
date: Wed, 29 May 2002 15:55:18 +0100 (BST)
from: Simon Tett <simon.tett@metoffice.com>
subject: Experiment description
to: r.battarbee@geog.ucl.ac.uk


Rick, Keith (as you may find it useful),
      here is some text on the experiments as promissed this morning.

Simon
The Hadley Centre is currently simulating the period 1500 to 2000
using its state-of-the-art atmosphere-ocean general circulation model,
HadCM3 (Gordon et al, 2000, Pope et al, 2000) driven with natural
forcings alone.  This model when driven with natural and anthropogenic
forcings has successfully simulated observed 20th century temperature
change (Stott et al, 2000).

The Hadley Centre plans to start a second simulation from 1750
conditions using both natural and anthropogenic forcings. The natural
forcing used are changes in solar irradiance, volcanic aerosol and
orbital parameters (mainly the date of perihelion). In this experiment
land-cover is set to estimated values for 1750 and concentrations of
CO2, CH4 and NO are set to their pre-industrial values of 277.6 ppmv,
790 ppbv and 396 ppbv respectively.

In the second experiment the Hadley Centre plans to simulate the
period 1750-2000 using natural and anthropogenic forcings staring from
initial conditions taken from the naturally forced simulation in
1750. The anthropogenic forcings which will be used are changes in
well-mixed greenhouse gases(as above plus changed in (H)(C)FCs),
sulphate aerosols (both their direct effect on scattering solar
radiation and their indirect effect on cloud albedo), changes in
vegetation (mainly the replacement of forest with pasture) and changes
in tropospheric and stratospheric ozone.

Due to the relative shortness of the instrumental record most
model-data comparisons use simulated variability in order to asses
consistency between simulation and observations. The real word record
is a combination of forced variability and internal variability. The
Hadley Centre's main aims in doing those two experiments is to test
the veracity of the simulated variability against proxy data. Simon
Tett is leading this work at the Hadley Centre and will provide
temperature, precipitation and THC strength to the project for
comparison against proxy reconstructions of climate. He will also help
develop procedures for model-data comparison.



@article{stott00,
  author       = {P. A Stott and S. F. B. Tett and G. S. Jones and M. R. Allen and J. F. B. Mitchell and G. J. Jenkins},
  title        = {External control of 20th century temperature by natural and anthropogenic forcings},
  journal      = {Science},
  year         = {2000},
  volume       = {290},
  pages        = {2133-2137}

@article{gordon00,
  author       = {Gordon, C. and Cooper, C. and Senior, C. A. and Banks, H. and Gregory, J. M. and Johns, T. C. and Mitchell, J. F. B. and Wood, R. A.},
  title        = {The Simulation of {SST}, sea ice extents and ocean heat transports in a version of the {H}adley {C}entre coupled model without flux adjustments},
  journal      = {Clim. Dyn.},
  year         = {2000},
  volume       = {16},
  pages        = {147-168}
}

@article{pope00,
  author       = {V. D. Pope and M. L. Gallani and P R Rowntree and R. A. Stratton},
  title        = {The impact of new physical parametrizations in the {H}adley {C}entre climate model -- {H}ad{AM}3},
  journal      = {Climate Dyn.},
  year         = {2000},
  volume       = {16},
  pages        = {123-146}
}



-- 
Dr Simon Tett  Managing Scientist, Data development and applications.
Met Office   Hadley Centre  Climate Prediction and Research
London Road   Bracknell    Berkshire   RG12 2SY   United Kingdom 
Tel: +44 (0)1344 856886   Fax: +44 (0)1344 854898 
E-mail: simon.tett@metoffice.com   http://www.metoffice.com

