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

Wednesday, 17 December 2014
Tianyu Jiang and Katherine J Evans, Oak Ridge National Laboratory, Oak Ridge, TN, United States
Surface thermal extremes are usually determined by large-scale circulation regimes. It has been shown that the model resolution is the key in simulating a lot of atmospheric phenomena. 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). 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 result indicates: 1) a general agreement on the first moment of climatological distribution with different resolution; 2) the higher resolution model can improve the high-order moments of the atmosphere circulation, including the weather regimes, which is critical to a reliable simulation and projection of the climate extremes.