| Summary: | University of Minnesota M.S. thesis. August 2019. Major: Soil Science. Advisor: Peter Snyder. 1 computer file (PDF); xii, 128 pages. Large-scale climate patterns affect many areas of our global environment either directly or indirectly. They provide the background conditions for regional climate patterns and weather events that in turn affect many areas of our society, such as agriculture, water supply, energy demand, and natural ecosystem development. Many scientists have analyzed how these large-scale modes of climate variability influence the climate response over North America on an individual basis, however, it is still unclear how the combination of modes of variability affect North American climate. In this study, I analyze the four leading modes of climate variability that influence North American climate patterns: the El Niño – Southern Oscillation (ENSO), the Atlantic Multidecadal Oscillation (AMO), the Pacific – North American (PNA) Pattern, and the Northern Annular Mode (NAM). Through an observational analysis, I show which climate pattern has the largest influence on a particular region of North America as well as the most common combinations of patterns to influence the continent. The oceanic patterns, ENSO and AMO, have the largest influence on the background conditions of regional climate due to their slow-varying nature, while the atmospheric patterns, PNA and NAM, have the largest influence on wintertime temperature and precipitation anomalies. The North American climate response of the combined PNA and NAM patterns is seasonally dependent, where in the boreal winter they have the largest influence when in opposition and in the summer when in the same phase. This is due in part to their common link with the Aleutian Low in the North Pacific. Furthermore, the AMO has a large influence on summer climate due to its weak seasonality and the lack of strength of the other regional climate patterns. Moreover, this study also presents an analysis on the North American climate influence of the ENSO and AMO using the NCAR CESM1 global climate model. The model results for the ENSO response are corroborated well with observations, however, the AMO response in the model is weak, which might be a result of the internal metrics of the model or a weak AMO forcing. The largest North American climate response occurs when the combined ENSO and AMO patterns are in opposition. The ENSO and AMO response is also simulated under RCP8.5 end-of-century conditions to analyze the pattern response under global warming. An eastward shift in the ENSO teleconnection occurs under future warming with the largest shift occurring under +ENSO conditions. An eastward shift occurs under –ENSO conditions only when in combination with a +AMO in the winter, suggesting the AMO having an influence on the ENSO teleconnection. Additionally, the shift in the ENSO response highlights the nonlinear nature of the ENSO teleconnection and an element of future climate change over North America.
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