| Summary: | Synoptic scale drivers, mainly extra-tropical cyclones, account for a majority of the day to day temperature variability in the mid-latitudes. This variability is at its greatest in the Northern Hemisphere in Boreal winter when the surface meridional temperature gradient is strong. Global warming has led to a reduction of the surface meridional temperature gradient due to the phenomenon of Arctic Amplification, where the Arctic has been warming at a faster rate than the mid-latitudes or tropics. Changes to the surface meridional temperature gradient will likely alter the baroclinicity of the mid-latitudes and thus extra-tropical cyclones. Understanding how extra-tropical cyclones and their associated temperature variability change in the presence of warming is vital to mitigating the potential outcomes such as an increased chance of heatwaves in regions with reduced variability or an increased chance of cold snaps that could negatively impact farmers in regions of increased variability. Using complementary ensemble empirical mode decomposition (CEEMD) to isolate the synoptic component of daily mean surface temperature, the evolution of the trend in synoptic temperature variability is analyzed. There has been a spatial in-homogeneity of synoptic temperature variability change ranging from -36.5% to 39.2% from 1948-2018 over the continental United States, Northern Mexico, and surrounding oceans. This variability is also temporally non-uniform. The first three decades experienced relatively large decadal rates of change, followed by a two-decade lull, where large regions experienced a reversal in the direction of synoptic temperature variability change. The last two decades have maintained the spatial structure observed in 1998 with the regions expanding in size and changing more quickly with time. Higher altitudes and surrounding regions generally see an increase in variability while elsewhere over land a reduction is observed. This creates a three-band structure over the continental United States. Averaged over ...
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