Unified Multiscale Operational Weather Forecasting at the Canadian Meteorological Centre
Seminar Room 1, Newton Institute
The genesis of the unified Global Environmental Multiscale model and forecasting system that was gradually deployed since 1997 will be presented. It was originally designed for both forecasting and data assimilation at uniform resolution global scale and variable resolution continental scale. It could also be run for mesoscale forecasting over smaller areas by increasing the stretching of the grid. The formulation of the model allowed it to be run either in hydrostatic or non-hydrostatic mode. Tangent linear and adjoint models were developed for variational data assimilation, and data assimilation was performed first using 3D Var and later 4D Var. More recently a global ensemble system was developed based on the GEM model for both ensemble forecasting and data assimilation. The modelling system has been generalised in different directions to become a complete environmental prediction system: emergency response, volcanic ashes, air quality, stratospheric ozone, wave modelling, coupling to rivers and oceans etc.
The development of a nested version of the model is having a profound impact on the forecasting system. After thorough testing, it was used successfully for operational forecasting at 1 km during the Vancouver Olympics in 2010 and it will become operational at 2.5 km over several windows in Canada. A large uniform resolution nested model has been shown to be equivalent to the variable resolution version for continental forecast and was implemented operationally. The nested version has allowed the development of a regional ensemble system. A replacement of the uniform resolution global grid by the composite Yin-Yang grid based on two uniform resolution limited-area grids is under study. Preliminary testing is showing this version to be equivalent in accuracy, but free of the “pole problem” affecting the grid point latitude-longitude models and much more suitable for future supercomputer architectures.