Continued Investigations of the Structure, Evolution, and Life Cycles of Intraseasonal Fluctuations of the North Pacific Jet Stream

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The jet stream over the North Pacific exerts a controlling influence on the procession of winter storms that cross the ocean to make landfall on the US and Canadian coasts. The role of the jet as a conveyor of storms makes it a topic of interest for weather forecasters as the paths and intensities of the storms are sensitive to the various forms of jet variability including extension, retraction and north-south meandering. Perhaps more importantly, jet variations can affect a succession of storms, so the influence of jet fluctuations extends beyond the typical five-day forecast and into the domain of subseasonal prediction. But the underlying dynamics of Pacific jet variations are not well understood and fundamental questions remain as to the mechanisms involved.The Pacific sector is unusual in its combination of middle-latitude jet dynamics, featuring the interplay between the jet and the weather patterns that move along it, and low-latitude influences from the region of deep convection over the warm waters of the western Pacfic. In earlier work one of the Principal Investigators (PIs) used a Linear Inverse Model (LIM) to identify a mechanism through which tropical influences interact with middle-latitude dynamics to produce upper-level circulation anomalies. In the present work the LIM analysis is applied to understand jet fluctuations identified using Self-Organizing Maps (SOMs). The work focuses on the dynamics of transitions from one jet state to another and the consequences of the transitions for downstream weather.The work is of societal as well as scientific interest given its connection to North American weather and relevance to long-range forecasting, as noted above. In addition, the PIs engage in public outreach including a monthly show on Wisconsin Public Radio. The project also provides support and training for two graduate students and two undergraduate summer interns.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.