IGCM paper

IGCM paper

(1) Summary of Forster et al.

(2) Changes since Forster et al. – reasons for changes

Here we list a number of changes which have been made to the version of the model described by Forster et al., and modified subsequently by Joshi et al.

(a) We reduced the default number of vertical levels from 22 to 7. This was to increase the computational speed of the model. Associated with this, were were able to increase the atmospheric timestep from 3/8 of an hour, to 1 hour. We also changed the vertical structure of the model levels, from a prescribed specific to the number of levels, to a structure equally spaced in pressure (see figure xx). In the 22 level case, there is some diffusion applied in the top two levels, of magnitude yy. In our 7 level version, apply this diffusion only in the top layer of the atmosphere, with a magnitude of zz. (b) There was a minor bug in the land surface scheme of the Forster et al version, in which the ground heat flux was……. We fix this in our version. (c) We closed the moisture budget. In the Forster et al version there is a parameterisation of snow melt, in which melted snow disappears from the system. In our version, we re-route this as runoff into the ocean. (d) Due to the modularisation of the slab seaice and slab ocean components of the model, we are able to increase the timestep of the ocean and seaice. In the Forster et al ocean and seaice, the timestep is the same as the atmosphere. In our version, we increase the ocean timestep to two days, and the seaice timestep to 6 hours. (e) We have added an option to run with a different convection scheme. This is the scheme of Tiedtke (xxxx). We use a version implemented in the SPEEDY model, with the following changes…..(David) (f) We modified the output of the model to be in netcdf and somewhat CF compliant (g) We completely restructured the code to make it more modular, so that different components could be swapped in and out.

We have carried out 3 tuning exercises with this model. These are (1) a multi-variate 1 dimensional tuning targeting surface mean temperature and precip (2) the ‘genetic Algorithm’ tuning described by Price et al, and (3) an ENKF tuning targeting surface temperature and precipitation. This essentially gives us 3 versions of the model. Here, we show results from the ‘GA’ version,

(3) Model climate – temperature and precipitation (with slab ocean, slab seaice), and comparison with observations. Surface energy fluxes? Sea ice? Comparison with Forster et al?

GENIE-2 paper

(1) Summary of different components (cite different GMD papers) (2) Coupling together of different components (e.g. timestep, where excess fluxes) (3) Non flux-corrected version – comparison with observations (4) Flux-corrected version – comparison with observations