Development of a limited-area 4d-VAR assimilation at MSC

The current Candian operational regional data assimilation system (RDAS) is based on the global variational analysis code. Although using innovations from the global variable resolution GEM model (run at 15 km over the uniform continental window), the same analysis code as for GDAS is used. This means T108 horizontal resolution is used in the inner loop of 4dvar. Increasing much further the resolution in the inner loop becomes problematical in terms of computer resources. At MSC, a limited area GEM-LAM model is being tested for NA-continental NWP in order to possibly replace the current regional global variable resolution GEM approach. A limited-area version of the GDAS 4dvar code was developed and is referred to as Meso4dvar. It can be run on the NA continental grid for short-range NWP (<48h) or more limited spatial extensions for very short-range NWP (<12h). The NLM and TLM horizontal resolutions of the NA-Meso4dvar is tested at 10 km and 35 km respectively. Basic formulation apsects and preliminary results will be described at the conference.