The Effects of the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation on U.S. Regional Weather
A climate researcher at Cornell University, Remy Mermelstein has written an interesting and provocative paper showing the linkage between the Pacific Decal Oscillation (PDO) and the climate swings in the United States on a region by region basis. The results of the study can be summed up in one graph: (click to enlarge)
This paper aims to identify and discuss the sensible weather trends in each of the ten climate regions of the U.S. affected by the natural oscillations representing the Pacific Decadal Oscillation (PDO) and the Atlantic Multi-Decadal Oscillation (AMO). By finding the correlations between the natural oscillations and the sensible weather, we can create composites and learn about their tendencies to better aid in forecasting the weather. The importance of the different modes of each oscillation has been found to vary among each of the climate regions of the U.S, as defined by the National Centers for Environmental Information (NCEI) (Karl, T. R. & Koss W. J., 1984) – Northwest, West, Southwest, Northern Rockies and Plains (West North Central), Upper Midwest (East North Central), South, Ohio Valley (Central), Southeast, and Northeast. It has been found that the different regions tend to be influenced differently by each of the oscillations and their modes, thus leading to variances in the regional sensible weather experienced in each mode’s time series. The most obvious effect on sensible weather that the AMO and PDO have can be seen from the temperature curves that are quite visible on the temperature time series (Kurtz, 2015). These indicate that the 1940-1978 decrease in CONUS temperatures was caused more by the negatively trending oscillatory modes of the AMO/PDO than other factors, and the 1978-2001 increase in temperatures was caused more by the positively trending oscillatory modes of the same oscillations. The small increase, or rather stagnant nature in U.S. CONUS temps since 2001, was likely due to peaking positive modes of the AMO/PDO. In the same way that the AMO and PDO can modify the regional temperatures, we see the same types of effects on precipitation, snowfall and drought in the different regions of the U.S.
Just as the sun rises and sets each day, thereby modifying our daily diurnal and nocturnal temperature cycles, the oceans also cycle and change on a regular and quite predictable time scale. On a daily, monthly, yearly and decadal scale, the oceans go through periods of warming and cooling on a large scale as the meridional overturning circulation (MOC) does its work transporting the oceans water around the world. Gilbert Walker has been recognized as one of the first to identify these periods of warming and cooling as oscillations, and oscillations that then have a profound effect on the weather trends across the globe, as early as 1908 (D’Aleo & Easterbrook, 2011). It was not until the late 1960s when these oscillations were first found to be statistically significant, and the weather community began to use them to predict and identify worldwide climate trends. It was not until 2003 (Anastasios, Swanson, & Kravtsov, 2003, 2007) that models were created that suggested that these cycles, namely the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) synchronized with each other. Using this as a base, we can explain the major climate shifts that have occurred since scientists began collecting data in the late 1800’s: 1908, 1932, 1973, and 2000. While the most noticeable change in these shifts was on global temperature, effects on the regional, sensible weather in the U.S. were also identified in these same time frames. Through analysis it has been theorized that these shifts are caused by the oceans, and are in fact the main drivers of the climate, and the sensible weather experienced in the United States (Klotzbach & Gray, 2009).
The PDO was first hinted at during the great climate shift/regime change in the Pacific Basin in the early to mid-1970s, and during a study conducted by scientists at NOAA to figure out why salmon fishing would go through 30 year cycles of amazing yields and not so amazing yields. Mantua et al., (1997) found that the PDO is essentially a long-lived El Niño-like pattern of the