cc: k.briffa@uea.ac.uk date: Wed, 29 May 2002 15:55:18 +0100 (BST) from: Simon Tett 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