General information

GEM is Environment Canada and Climate Canada's Global Environmental Multiscale (GEM) weather and seasonal forecast model. Most of the source code is written in Fortran. Just a few basic routines are written in C. The call of the executable is surrounded by pre- and post-processing shell and Python scripts. A hand full of configuration scripts allow the user to set basic parameters.

At the ESCER Centre of UQAM we take a copy of GEM and modify the code and scripts to convert the weather and seasonal forecast model into a climate model. The main differences between GEM and GEM-UQAM are:

• The scripts of GEM-UQAM are changed to run simulations by month and to store the output in monthly directories.
• GEM-UQAM contains the option to use the land surface model: CLASS (Canadian Land Surface Scheme)
• GEM-UQAM contains the option to use the 2D lake model: FLake
• In GEM-UQAM all accumulators are averaged and therefore "per second" must be added to accumulator units.

Depending on the version, the official name of the UQAM version of GEM is:

      "Developmental version of CRCM5/GEM3, CRCM6/GEM5"
      "MRCC5/GEM3, MRCC6/GEM5 en développement"

Grids

GEM5 supports rotated lat-lon grids:

• global uniform
• global YinYang (two LAM grids, each covering a little more than half the globe, overlapping like a tennis ball)
• regional LAM (Limited Area Model) grids

Grids of GEM version 4 and up are horizontally (Arakawa C-grid) and vertically staggered.