Variability in wintertime position and strength of the North Pacific jet stream as represented by re‐analysis data

Abstract

AbstractThe popular National Center for Environmental Prediction (NCEP)/National Center for Atmospheric Research (NCAR) re‐analysis database was used to create a mean winter seasonal jet stream database for the northern Pacific Ocean region for the period 1948–1949 through 2004–2005. Grids of mean seasonal 300 hPa scalar wind were used to determine the latitudinal position of the primary mid‐latitude jet on a longitudinal resolution of 2.5° from eastern Asia to western North America. The position and strength of the jet stream across this region are key determinants of winter precipitation variability downstream across the predominantly arid western region of North America.Results show that the latitudinal position of the jet exhibits greater variance over the eastern half of the northern Pacific Ocean, while the greatest variance in the speed of the seasonal jet occurs across the central northern Pacific Ocean. A statistically significant increase in the speed of the mean seasonal jet occurred over the central area of the northern Pacific Ocean during the last half of the 20th century. A spatially consistent but statistically insignificant trend toward a more southerly position of the jet occurred during the study period. The results do not confirm current theories of a general pole‐ward shift in mid‐latitude jet streams in association with recent and future climate change, suggesting that such an observed or theoretical hemispheric shift may not necessarily be evident within a particular region or that any shift over the last 50 years has been less than the 2.5° resolution of the NCEP/NCAR dataset. The jet stream data support the connection between the jet and the Pacific‐North American atmospheric teleconnection pattern and between the jet and the oscillation of sea surface temperature anomalies in the northern Pacific Ocean known as the Pacific Decadal Oscillation. Copyright © 2008 Royal Meteorological Society