An Attempt at Resolving the Western North American Enso Precipitation Dipole within Large-Scale Tree-Ring Networks

Abstract

Previous research has identified the El Niño Southern Oscillation (ENSO) as a main driver of North American precipitation west of the Rocky Mountains. ENSO drives a precipitation pattern that is best characterized as a dipole, with the dipole centered near 40° N and the opposing zones of precipitation anomalies occurring in the Pacific Northwest and American Southwest. To explore the long-term spatiotemporal variability associated with the ENSO modulated precipitation dipole, 522 western North American tree-ring chronologies were screened for sensitivity to instrumental and pre-instrumental ENSO variability and cool season moisture, producing two networks of tree-ring chronologies. To asses if the networks of tree-ring chronologies yielded a dipole pattern of growth during ENSO events, the instrumental and paleo networks of regionalized tree-ring chronologies (north and south of 40ºN) were evaluated based on the records of tree-ring growth during ‘moderate’ and ‘extreme’ ENSO event years. Results show a majority of tree-ring chronologies may not be sensitive enough to capture ENSO-driven climate perturbations, or, at least not on a direct annual event basis, and fail to document a related North American dipole pattern. The lacking ability of the tree-ring chronologies to resolve a dipole pattern that mimics the ENSO precipitation dipole pattern, supports and is in-line with previous tree-ring dipole research (Dettinger et al. 1998; Cook et al. 2004; St. George 2014). Further research using a more extensive network of tree-ring data, with more thorough testing for useful ENSO precipitation-correlation thresholds, and additional exploration of the spatial extents and climatic windows that may be ideal for detecting the spatiotemporal variability of ENSO dipole and could potentially yield more definitive results.