Change of mean midlatitude westerlies in 21st century climate simulations

Changes in midlatitude westerlies over the Pacific jet region between the 20th century and 21st century in general circulation models participating in the recent IPCC‐Forth Assessment are delineated. Outputs derived from individual models reveal that in almost all models analyzed the seasonal mean midlatitude jet streams in the northern hemispheric Pacific and west Atlantic during boreal winter and in the southern hemispheric Pacific during boreal summer are significantly intensified in warmer 21st century climate compared to the state in the 20th century at the upper part of the core, at 200‐100 mb.