Validation of synoptic circulation patterns simulated by the Canadian climate centre general circulation model for western North America - Research note

In order to assess the ability of a GCM to simulate regional to synoptic scale atmospheric structures, a correlation-based computer-assisted gridded map typing procedure is used to compare daily pressure (MSL) and geopotential height fields (500 hPa) from a GCM simulation of the present climate to a decade of NMC analyses. The model is able to reproduce the entire range of synoptic circulation types. However, statistically significant differences in the seasonal frequencies and variances of the main circulation types are evident. These differences, which are most pronounced in the winter (at 500 hPa) and in spring and autumn in the MSL fields, are consistent with subtle errors in the predicted fields at the hemispheric scale. The lack of agreement between the NMC climatology and the ''control'' simulation precludes extension of this approach to investigation of climate change impacts in western north America, and to more meteorologically dynamic extra-tropical regions. The map-typing procedure is shown to be an appropriate GCM synoptic-scale validation tool that permits direct comparison of GCM output and observed fields. As such, it has the potential to elucidate the regional-scale impacts of global climatic change through established synoptic circulation environment relationships.