Optimal Ranking Regime Analysis of U.S. Temperature Variability: 1896-2012

The Optimal Ranking Regime (ORR) method was used to identify intra- to multi-decadal (IMD) time windows containing significant ranking sequences in U.S. climate division temperature data. The simplicity of the ORR procedure's output – a time series' most significant non-overlapping sequences of high or low rankings – makes it possible to graphically identify common temporal breakpoints and spatial patterns of IMD variability in the analyses of the 102 climate division temperature series. This approach is applied to divisional annual and seasonal temperature data during 1896-2012, annual AMO and PDO climate indices, and an annual northern hemisphere temperature series. While PDO phase appears to be an important influence on spring temperatures in the northwest U.S., AMO-synchronous effects are more apparent over the east in annual, winter, summer and fall temperatures. Annual AMO values also correlate significantly with fall temperatures in the southwest. The cause and duration of the eastern U.S. warm hole period - identified here as a cool temperature regime occurring between the late 1950's and late 1980's – is discussed.