Simulating Global and North American Climate Using the Global Environmental Multiscale Model with a Variable-Resolution Modeling Approach

Abstract Results from two simulations using the Global Environmental Multiscale (GEM) model in a variable-resolution modeling approach are evaluated. Simulations with a highly resolved domain positioned over North America and over the tropical Pacific?eastern Indian Ocean are assessed against the GEM uniform grid control run, 40-yr ECMWF Re-Analysis (ERA-40), and available observations in terms of regional and global climate and interannual variability. It is found that the variable-resolution configurations realistically simulate global and regional climate over North America with seasonal means and variability generally closer to ERA-40 or observations than the control run. Systematic errors of the control run are still present within the variable-resolution simulations but alleviated to some extent over their respective highly resolved domains. Additionally, there is some evidence of performance deterioration due to the increased resolution. There is little evidence that an increased resolution over the tropical Pacific?eastern Indian Ocean, with better-resolved local processes (e.g., convection and equatorial waves), has a significant impact on the extratropical time mean fields. However, in terms of simulating the Northern Hemisphere atmospheric flow anomaly associated with the dominant mode of sea surface temperature interannual variability in the equatorial eastern Pacific (i.e., El Niño), both stretched configurations have more realistic teleconnection patterns than the control run.