Seminar Abstract

James Johnstone

Tuesday, April 6, 2010

A quasi-biennial signal in Western U.S. hydroclimate and its global teleconnections

While ENSO is known to produce north-south shifts in the Western U.S. winter precipitation distribution, relatively little is known about systematic hydroclimate variability at central latitudes, and over the region as a whole. This talk explores the nature and possible origins of a significant ~26-month quasi-biennial (QB) oscillation in regional winter precipitation, a signal that appears to maintain ‘clockwork’ regularity from the mid-20th century to recent months. The oscillation in precipitation is most prominent from central California to southern Idaho, where its influence exceeds that of ENSO over most of the Western U.S. The precipitation cycle is traced to a regional oscillation of tropospheric pressure and wind on over the North American Pacific coast, and more broadly to a hemispheric-to-global scale annular mode pulsation. Tropospheric QB variability is compared to the prominent QBO of the equatorial stratosphere and to known QB modes of the solar magnetic field.