Observed trends in the global jet stream characteristics during the second half of the 20th century

Abstract

In this paper, we propose a new method based on the detection of jet cores with the aimto describe the climatological features of the jet streams and to estimate their trends inlatitude, altitude, and velocity in the National Centers for Environmental Prediction(NCEP)/National Center for Atmospheric Research (NCAR) and 20th Century reanalysisdata sets. Due to the fact that the detection method uses a single grid point to define theposition of jet cores, our results reveal a greater latitudinal definition allowing a moreaccurate picture of the split flow configurations and double jet structures. To the best of ourknowledge, these results provide the first multiseasonal and global trend analysis of jetstreams based on a daily-resolution 3-D detection algorithm. Trends have been analyzedover 1958–2008 and during the post-satellite period, 1979–2008. We found that, ingeneral, trends in jet velocities and latitudes have been faster for the Southern Hemispherejets and especially for the southern polar front jet which has experienced the fastest velocityincrease and poleward shift over 1979–2008 during the austral summer and autumn.Results presented here show an acceleration and a poleward shift of the northern andsouthern winter subtropical jets over 1979–2008 that occur at a faster rate and over largerzonally extended regions during this latter period than during 1958–2008