Surface Temperature Extremes and Detectable Trends in Northern Hemisphere Mid-Tropospheric Planetary Wave Pattern Occurrence and Persistence

Abstract:

The occurrence of extremely hot and extremely cold days has been linked to the propagation and persistence of mid-tropospheric planetary waves. Here, we utilize self-organizing map (SOM) cluster analysis to determine the occurrence, persistence, and maximum duration of mid-tropospheric planetary wave patterns from the 1979 to 2013 and 1990 to 2013 periods in the ERA-Interim, NCEP/NCAR R1 and NCEP-DOE R2 reanalysis 500 mb geopotential height fields. We conduct seasonal analyses of seven northern hemisphere mid-latitude domains and determine circulation pattern matches between reanalysis datasets using rmse and pattern correlation metrics. We consider a particular spatial pattern within a given domain to exhibit a robust trend in either occurrence or persistence when a matching pattern from all three reanalysis datasets exhibits a statistically significant trend over the chosen analysis period. We find robust trends in a limited number of domains, including less frequent troughing events over central North America in the winter months for the 1979 to 2013 period, more frequent and longer maximum duration ridging events over central/eastern Europe and western Asia in the summer months for both periods, and longer maximum duration ridging events over the eastern Pacific/western North America during the winter months for the 1990 to 2013 period. In regions that exhibit a robust trend in a particular mid-latitude wave pattern, we test whether such a trend in circulation can be linked to the occurrence of extreme hot/cold surface temperature events. Lastly and conversely, we assess the fraction of temperature extreme trends that can be attributed to changes in the occurrence or persistence of particular wave patterns.