Non-Gaussian Cold-Side Temperature Distribution Tails and Associated Synoptic Meteorology

Abstract

Abstract Non-Gaussian cold side temperature distribution tails occur in spatially coherent patterns in winter and summer across the globe. Under such conditions, future changes in extreme cold temperature exceedances may be manifested in more complex ways than if the underlying distribution were Gaussian. For example, under a uniform warm shift, locations with shorter- or longer-than-Gaussian cold side tails would experience a more or less rapid decrease in the number of extreme cold threshold exceedances, respectively, compared to if the tail were Gaussian. In many places in the mid- to high latitudes, shorter-than-Gaussian cold tails occur where there is a climatological limit on the magnitude of cold air to be transported by synoptic flow. For example, some high-latitude regions are already among the coldest in the hemisphere, thus limiting the availability of extremely cold air, in an anomalous sense, that can be transported to the region. In other short tail regions, anomalously cold air originates from or travels over large water bodies, which limits the magnitude of the cold anomaly. Long tails are often present when the cold source region is downstream of the climatological flow, requiring a highly anomalous circulation pattern to transport the cold air. The synoptic evolution of extreme cold days at several short- and long-tailed weather stations are presented to help diagnose the mechanisms behind extreme cold temperatures under conditions of non-Gaussianity. This provides a mechanistic view of how extreme cold occurs at each location, as well as an explanation for the notable deviations from Gaussianity.