**5.1.1 RegCM 4.1.1 exploitation on the GRID**

RegCM4 is the fourth generation of the regional climate models originally developed at the National Centre for Atmospheric Research (NCAR) and currently being developed at ICTP, Trieste, Italy. It was released in June 2010 as a prototype version RegCM4.0 and as a complete version RegCM4.1 in May 2011 (Giorgi 2011). A bug fixing release RegCM4.1.1 was then released in June 2011.

The RegCM4.1 package now uses dynamic memory allocation in all its components. The whole output subsystem is now able to produce NetCDF format files, which is in better compliance with the standard Climate and Forecast Conventions.

The RegCM modelling system has four components namely Terrain,sst,ICBC, RegCM and some postprocessing utilities. Terrain sst and ICBC are the three components of RegCM preprocessor:

Th first step will define the domain of the simulation: the executable terrain horizontally interpolates the landuse and elevation data from a latitude-longitude grid to the cartesian grid of the chosen domain.

Sst executable then creates the Sea Surface Temperature file. Finally the ICBC program interpolates Sea Surface Temperature (SST) and global re-analysis data to the model grid. These files are used for the initial and boundary conditions during the simulation.

The pre-processing phase will therefore need to read global re-analysis data (size of the order of several dozen GB for each year of simulation) and will produce a large size of input data as well. RegCM itself produces than a large amount of output data.

As an example, a monthly run on domain of 160x192 points will produce around 10 GBytes of data, which means around 10 TBytes of data are produced for a climate simulation lasting a century. This data needs to be locally available, as a remote file system would slow the simulation down dramatically.

The greatest challenge in running RegCM on the GRID is therefore handling the data properly.
