GEM-MACH10: Implementation of a New Higher-Resolution Version of the Canadian Operational Air Quality Forecast Model

GEM-MACH15 has been Environment Canada's operational regional air quality forecast model since November 2009. GEM-MACH15 is a limited-area configuration of GEM-MACH, an on-line chemical transport model that is embedded within GEM, Environment Canada's multi-scale operational weather forecast model. It is run twice daily to produce 48 hour forecasts of hourly O3, PM2.5, and NO2 fields over a North American grid with 15 km horizontal grid spacing, 58 vertical levels from the surface to 0.1 hPa, and a 450 s time step. A new model version, called GEM-MACH10, has been developed for operational implementation. It uses 10 km horizontal grid spacing, 80 vertical levels, a 300 s time step, updated model source code, and updated emissions.

The computational cost of GEM-MACH10 is roughly a factor of four larger than that of GEM-MACH15 due to the increased spatial resolution. The improved forecast performance resulting from these changes will be described and some of the challenges encountered in developing this new model version will also be discussed.