Section 9.3 The Jet Stream
fast-flowing westerly current flowing between circulation cells
200-250 mbar level, 100-400 mph
essentially driven by geostrophic balance
caused by temperature differences between air near equator and air near the pole
migrates depending upon the season (along with other circulation cells)
The polar jet stream is the more prevalent than subtropical jet
It occurs along a major frontal zone, the polar front.
The jet stream moves faster in winter.
tends to migrate southward in the winter
The jet streams meander like rivers, producing a wavelike pattern of troughs and ridges
The air flow through these waves results in storms that move warm air poleward and cold air toward the equator
Each trough-ridge combination is called a Rossby wave
Drift slowly eastward, with rising air near the troughs and sinking air near the ridges
trough-ridge combinations at 500 mb level and higher
characterized by wavelength and amplitude
important for development of surface systems!
short waves (<6000 km) may be embedded in long waves
move relative to longwaves (20-40 mph eastward)