Simulating North American Heat Waves and Large scale Weather Regimes in climate models: Circulation Characteristics and synoptic-scale activity

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Wednesday, 7 January 2015
Tianyu Jiang, ORNL, Oak Ridge, TN; and K. Evans

Surface thermal extremes are usually determined by large-scale circulation regimes. In this study, the summertime heat waves in North America and the associated ridging/blocking activity are characterized using reanalysis data and global climate models with different horizontal resolutions (~120 km / ~30 km) and ocean modules (prescribe/interactive). It has been shown that the model resolution is the key in simulating a range of of atmospheric phenomena. The typical synoptic features accompanying the heat waves are depicted. The frequency of occurrence and intensity of the upstream blockings are examined. The discrepancy between the reanalysis and the models on the heat wave characteristics as well as the upstream blocking activity is assessed by comparing the passage of synoptic-scale transients and its local reinforcement to the anticyclonic circulation. The results indicate: 1) a general agreement on the first moment of climatological distribution with different resolution; 2) the higher resolution model can improve the higher-order moments of the atmosphere circulation, including the weather regimes, which is critical to a reliable simulation and projection of the climate extremes.