Arctic and Tropical Influence on Extreme Precipitation Events, Atmospheric Rivers, and Associated Isotopic Values in the Western U.S.

Friday, 19 December 2014
Staryl E McCabe-Glynn1, Kathleen R Johnson1, Yuhao Zou1, Jeffrey M Welker2, Courtenay Strong3, Jonathan J Rutz4, Jin-Yi Yu1, Kei Yoshimura5, Scott L Sellars1 and Ashley E Payne1, (1)University of California Irvine, Irvine, CA, United States, (2)University of Alaska Anchorage, Anchorage, AK, United States, (3)University of Utah, Salt Lake City, UT, United States, (4)NOAA, Boulder, CO, United States, (5)Atmosphere and Ocean Research Institute University of Tokyo, Tokyo, Japan
Extreme precipitation events along the U.S. West Coast can result in major damage and are projected by most climate models to increase in frequency and severity. One of the most prevalent extreme precipitation events that occurs along the west coast of North America are known as 'Atmospheric Rivers' (ARs), whereby extensive fluxes of water vapor are transported from the tropics and/or subtropics, delivering substantial precipitation and contributing to flooding when they encounter mountains. This region is particularly vulnerable to ARs, with 30-50% of annual precipitation in this region occurring from just a few AR events. Because of the tropical and/or subtropical origin of ARs, they can carry unique isotopic properties. Here we present the results of analysis of weekly precipitation data and accompanying isotopic values from Giant Forest, in Sequoia National Park, in the southwestern Sierra Nevada Mountains (36.57° N; 118.78° W; 1921m) from 2001 to 2011. To better characterize these events, we focused on the 10 weeks with the highest precipitation totals (all greater than 150 mm) during the study period. We show that nine of the top ten weeks contain documented 'AR' events and that 90% occurred during the negative phase of the Arctic Oscillation. A comparison of extreme precipitation events across the Western U.S. with several key climate indices demonstrate these events occur most frequently when the negative phase of the Arctic Oscillation is in sync with the negative phase of the El Niño Southern Oscillation (ENSO) and the negative or neutral Pacific North American (PNA) pattern. We also demonstrate that central or eastern Pacific location of ENSO sea surface temperature anomalies can further enhance predictive capabilities of the landfall location of extreme precipitation. Stable isotope results show that extreme precipitation events are characterized by highly variable δ18O (-7.20‰ to -19.27‰), however, we find that more negative δ18O values typically occur during the negative PNA pattern. Finally, we will present the results of data comparison with NCAR-NCEP reanalysis, Hysplit back trajectories, and isotope enabled climate model (IsoGSM) results.