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Section 9.3 The Jet Stream

NOAA Jetstream:

  • 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

Seasonal Variations

  • 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

Rossby Waves

  • 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

    • smaller-scale disturbances

    • move relative to longwaves (20-40 mph eastward)