On the average, there are two jet streams present in the Nort h e rn Hemisphere (figure
21, page 33). The polar jet is found in latitudes 30°-60°N. The subtropical jet is located
between 20-40° N and has a distinct cloud signature which is evident on satellite images
( f i g u re 22). An important characteristic of jet streams is that wind speed is not uniform
within the jet. There exists a jet core or streak which contains the maximum winds. The
location and movement of the jet s t re a kis a key factor in cyclone development.
The jet streak moves along the jet stream in a manner similar to the way a short wave
trough moves through the long wave pattern. Jet streaks move slowly relative to the
wind parcels that travel along the jet stream. Jet streaks are analogous to constricted
areas in a river. A parcel of air traveling along the jet stream will overtake the jet streak
and be temporarily accelerated before exiting the region.
figure 22. GOES image, January 7, 1994, 1100 CST
image courtesy of M. Ramamurt h y, University of Illinois, Urbana/Champaign