Reframing North Pacific atmosphere dynamics for western US streamflow

This paper explores a new statistical approach for defining cool-season PNA-like dynamics, between the Aleutian low and Pacific high, as they relate western US streamflow variability and drought. High elevation snowpack, delivered from the Pacific Ocean through cool-season storms, is a primary source of moisture for major rivers of the western US. Studies through the past several decades have recognized that the western US hydroclimate is influenced by the intensity and phasing of ocean and atmosphere dynamics and teleconnections, such as ENSO, and North Pacific variability. This combination of influences is realized in circulation patterns along the west coast of North America. Here, cool-season synoptic scale patterns can encourage "forking" or "blocking" of eastward moisture flow from the Pacific, which can direct the winter storm track and the spatial patterns of moisture delivery to western US watersheds. Traditionally, atmospheric indexes that describe these atmospheric/oceanic circulations have been based on values from fixed points in space or EOF loadings have been used to measure these dynamics. This study explores how collective search agents can be used to quantitatively measure the position, magnitude, and shape of moving atmosphere features, and in particular, the Aleutian low and Pacific high. Initial results yield time series of the position and magnitude of these semi-permanent cool-season atmospheric features. As we show for the Klamath River basin, these series can be combined to create specialized indexes of atmosphere dynamics, emphasizing the unique relationship between these features and hydroclimatic variability, including drought, for specific river basins. Further work is being done to effectively measure the shape of features, generalize the method so as to apply it to other dynamic phenomena, and finally, show how annual-resolution paleoclimatic tree-ring reconstructions might be made to extend these dynamic relationship metrics back through time.