Large-scale regime transitions and atmospheric river landfalls across western North America

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atmospheric rivers , teleconnections , Pacific North American pattern , Student Showcase of Research & Engagement 2018
Webber, Sam
Recent studies suggest a potential relationship between flow patterns described by the Pacific North American (PNA) teleconnection pattern and landfalling atmospheric rivers (ARs) over western North America. This relationship illustrates an on average positive to negative trend in the PNA in the days leading up to and after a landfalling AR along the California coastline. The goal of this study is to extend prior research by specifically investigating large-scale regime transitions over the Northeast Pacific as described by transitions in the PNA and their relation to AR landfall events. Regime transitions are defined as a change of at least one standard deviation in the PNA index value in seven days. The methodology cross-references archived daily PNA values with NCEP-NCAR Reanalysis-derived sub-daily IVT magnitudes and AR landfalls for locations along the western North American coast between Alaska and the California Baja from 1950 to 2015. Analysis of a time-lagged composite time series of all transitioning PNA events for a +0.5 to -0.5 (-0.5 to +0.5) transition illustrates a statistically significant increased (decreased) likelihood of landfalling ARs at the British Columbia coast between Day -4 and Day -0 and a statistically significant decreased (increased) likelihood from Day +5 to Day +10.